Why Haven’t Humans Speciated?

Nov 21, 2013


Discussion by: godzillatemple

All right, I have finished reading "The Greatest Show on Earth" and "Climbing Mount Impossible".  Next on my reading list is "The Blind Watchmaker", after which I hope to finally tackle "The Selfish Gene" (and yes, I realize I am doing this backwards).  Hopefully, this will stave off the "why don't you just go read a book" responses the last time I asked a question about evolution…

My current understanding of "speciation" is that it occurs when two segments of a population diverge sufficiently that the members of the two segments either cannot or do not interbreed.  The "do not" bit confuses me a bit, since sometimes it seems to involve something as seemingly trivial as slightly different-colored plumage and it's hard to see why one group should be considered a different species if it is actually cross-fertile with another group (via in vitro fertilization, say) and the resulting offspring is not sterile.  That  may or may not be relevant to this discussion, however.

With regard to what causes speciation, my current understanding is that it usually happens when populations become separated and isolated from other populations of the same initial species, whereby natural selection then has a chance to work differently on the different groups over time.  I have also read that this process can actually occur over relatively short time spans (hundreds of years or even less), especially for organisms with short breeding cycles.

Finally, my current understanding is that the wide variation observed between the various "races" (and I use the term cautiously) of humanity are the result of different groups becoming separated and isolated for tens of thousands of years.  I don't really want to get into a discussion of what "race" actually means or how sharply the lines between different races are currently defined, but I think it's safe to say that natural selection worked differently on populations who lived in extreme northern climates compared to those who lived in the tropics, for example.  And yet, despite this fact, we are all obviously the same species since we can (and do) interbreed with no problems (my wife and I are different races entirely, and yet we not only wanted to interbreed we also have successfully done it…)

So here's my question.  Assuming everything I just said is accurate, why don't we have multiple species of humans?  Based on everything I've read, the separated populations that gave rise to the different races were certainly isolated long enough for speciation to occur.  And yet, it apparently didn't.  I've given this a lot of thought and have come up with a few possible answers:

  • Since humans have longer life spans and breeding cycles than, say, finches, thousands of years of isolation isn't really long enough for human speciation to have occurred after all. [Do we have evidence of other animals with long life spans that speciated over shorter time periods?]
     
  • Since humans have evolved intelligence, we are no longer driven solely by chemical and visual clues that prevent other animals from interbreeding with slightly different members of the parent species.  [Do we have evidence that other "intelligent" species such a dolphins or chimpanzees have also avoided speciation?]
     
  • Perhaps humans were already almost completely adapted to their environment at the point that populations started becoming isolated, so any further changes after that point would necessarily have to be minor. [Is it fair to say that adapting to life on the sub-Saharan plains is anywhere close to being "completely adapted" to life in the Arctic Circle?]

Any thoughts?  I realize there may not actually be a definitive answer, but I'd love to see what other people who know more about the subject think about it.

95 comments on “Why Haven’t Humans Speciated?

  • You and your wife are not “entirely different races.” There is only one race of humans, the human race. Different “races” would be equivalent to “subspecies.” There were several different races (subspecies) of Darwin’s finches…different species.

  • I don’t know much biology but your question is pretty basic so I think even I can answer it. First of all the question is one of those very general questions that there isn’t really one easy answer to. Asking “why didn’t species X turn into two species at time T” doesn’t necessarily have an obvious answer for all species at all times. It would be a much better defined question if you had some example that indicated we might expect two species, such as the finches. I guess you think that the differences in race are such an example but they aren’t. Racial differences are primarily a social construction. From a biological standpoint the slight differences in skin pigment, hair texture, and a few other traits are minimal. You wouldn’t for example ask “why can left handed people mate with right handed people” or “why can tall people mate with short ones” but I’m pretty sure the corresponding variation in the genes in those cases is roughly equivalent with the percentage of traits we associate with race.



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  • 3
    BanJoIvie says:

    I think your first 2 answers to your own question sound convincing. They both accord with my (limited, layperson’s) understanding of human evolution. I would not be surprised if both ideas have played a role in maintaining a single breeding population of modern humans.

    Your third answer doesn’t click as well for me.

    I might offer a (purely speculative) variant on the idea. Humans were not necessarily “almost completely adapted” to their various environments, but certain cultural adaptations (clothing, tool use, agriculture, etc.) have allowed humans to avoid – or at least to greatly ameliorate – the reproductive consequences of certain maladaptive traits in many environments. In other words, selective pressure which might have driven isolated human populations to adapt genetically to their new environments has been greatly lessened by humans ability to adapt memetically at a much more rapid rate.

    That is not to say that humans are immune from natural selection, merely that the pressures driving human evolution may be more uniform across environments than we might expect in a less culturally adaptive species.

    A fourth possible factor occurs to me as well. The isolation of various populations may not have been as complete as it appears. I am often surprised to learn just how much travel and interbreeding has occurred – over remarkable distances – between various groups of humans. Often the assumption that a single group of travelers arrived and peopled a region is later replaced by the discovery of subsequent waves of immigration and various forms of cultural exchange (from elaborate trade routes to various forms of raiding and pillaging.)



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  • 4
    SurLaffaLot says:

    Of the group of ancestors called hominids, humans are the last species to survive. It is those other species of hominids which have gone extinct, as have some 95% of all species, of all life, which have ever lived. Humans of today, (homo sapiens), are not in isolation of one another, and the various ethnic groups alive today interbreed willy-nilly, so the principle of isolation does not apply.

    BTW, the delineation between one species and another can actually be quite blurry. One species may be capable of interbreeding with another, something simply stops it from happening, eg. an exclusive tendency of a species to only breed with other members of the same species; eg. {tigers cross lions}, and {horses cross donkeys} can interbreed.



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  • 5
    Seraphor says:

    Based on everything I’ve read, the separated populations that gave rise to the different races were certainly isolated long enough for speciation to occur.

    Is that so?

    First off, this relies on information about how isolated human populations have been to be accurate, which I’m not sure it is, and would be impossible to ascertain anyway.

    Secondly, evolution doesn’t only work on time scale, it depends on environmental pressure as well. But even taking that into account you couldn’t necessarily say what amount of time is ‘enough’ for speciation.

    Speciation is a definition dependent on the results of evolution, not the process itself. It depends on two populations of one species being unable to produce fertile offspring. Now this can happen for any number of reasons and is likely down to the specific way in which the species have evolved, not the amount they have evolved. Certain gene combinations will likely be more compatible or incompatible than others.

    I would wager that you could put two populations of one species, and place them both under the same conditions that would result in speciation, so you’d have four populations or two groups of two. Group 1 with populations A and B, and group 2 with populations A and B. 1A and 1B could drift so far apart that they became two separate species, while 2A and 2B could evolve just as much and just as differently from each other and still be able to interbreed.

    Also, take canines. There are thousands of breeds of dog, many of them are wildly different from each other, far more so than the different human ‘races’, and yet these are all still able to interbreed. They have evolved to the point where they’re a separate species from wild wolves as they were domesticated thousands of years ago, but they haven’t evolved away from each other as they’ve been interbreeding throughout those thousands of years despite the artificial selection processes that made them.

    I’d say a similar thing can be said for human ‘races’. We’ve been permanently cut off from our most closely related species due to them dying off, which amplifies the differences we have with them. But populations of the human race haven’t been separated long enough or consistently enough to have made that much of a leap, and due to our modern civilization being a global one, probably never will.



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  • 6
    SaganTheCat says:

    humans move about very quickly, it didn’t take long to cover the planet then there were no geographical islands left.

    it comes down to the definition of species as always. some seperate species of animal could interbreed, and don’t. given long enough (which is entirely variable as it involves random genetic mutations) 2 species will become incapable of interbreeding but long enough could in essence mean millions of years for a species that breeds annually.

    alternatively, some humans on remote islands may have been genetically incapable of breeding with other humans, we don’t know because they would have gone silently exctinct since they possibly had no phenotipical differences

    there may be individuals right now that due to a mutation can’t breed with other humans, only ones with the same mutation. again their line will go exctinct without anyone knowing.

    global travel makes it as good as impossible to speciate now. cultural attempts to seperate groups are doomed to failure as cultures evolve faster than organisms. but the term “species” is too vague and was coined long before evolution was understood.

    hominids speciated when they were able to. when groups left africa and were seperated long enough to take a different evolutionary path, like neaderthals, but even this happened recently in evolutionary terms. bipedal apes can cover vast distances in little time so whose early speciation experiments were doomed to fail with the coming of modern H sapiens.

    Seperation needs to last a very long time. the genetic evidence for human/chimp seperation suggests interbreeding could have continued for millions of years between the beginning of the split and the point where never the twin met (possibly a long time after before there was a chromasomal barrier).

    you need to start moving to new planets if you want to see the species split. or wipe out 90 odd % and see what happens



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  • Being a novice in this field, I certain make no claim to be a biologist of any type, I do however think I understand the question and answers given thus far. As Darwin discovered, variations in species, particularly on the Galapagos and surrounding islands for instance were speciated due to a particular animal, bird whatever migrating to isolated islands and over time adopting to a particular environment. in some cases that would lead to that species thriving and evolving or the complete opposite, extinction.
    So hypothetically would it have been possible for an element of early H Sapien to have migrated to a sub-terrainien environment and over thousands, maybe millions of years evolved into a sub species of H- Sapien. This of course manifesting itself in maybe larger eye orbitals, enhanced low light vision or even virtual blindness along with depleted skin melamine etc. Is this the type of thing we are talking about? Surely that then would be our species evolved in a different way, another branch as it were.



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  • Being a novice in this field, I certain make no claim to be a biologist of any type, I do however think I understand the question and answers given thus far. As Darwin discovered, variations in species, particularly on the Galapagos and surrounding islands for instance were speciated due to a particular animal, bird whatever migrating to isolated islands and over time adopting to a particular environment. in some cases that would lead to that species thriving and evolving or the complete opposite, extinction.
    So hypothetically would it have been possible for an element of early H Sapien to have migrated to a sub-terrainien environment and over thousands, maybe millions of years evolved into a sub species of H- Sapien. This of course manifesting itself in maybe larger eye orbitals, enhanced low light vision or even virtual blindness along with depleted skin melamine etc. Is this the type of thing we are talking about? Surely that then would be our species evolved in a different way, another branch as it were.



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  • 9
    SaganTheCat says:

    actually a simpler answer would be because humans adapt their environment, reducing the opportunity for nature to select. a human with no evolved mutations could live just as happily along the equator or inside the arctic circle, just as long as they can afford food and heating/aircon costs.



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  • 10
    Alan4discussion says:

    @OP – With regard to what causes speciation, my current understanding is that it usually happens when populations become separated and isolated from other populations of the same initial species, whereby natural selection then has a chance to work differently on the different groups over time.

    That is so, but it works over vast numbers of generations.

    I have also read that this process can actually occur over relatively short time spans (hundreds of years or even less), especially for organisms with short breeding cycles.

    Only this quickly with organisms (such as bacteria) with short breeding cycles.

    Modern humans, like all life, are “speciating, but the process is only in the early stages of separating races. Human populations are simply too mobile for populations to be isolated for long enough for the process to progress in separating sections of the gene pool.

    There are however minor variations in particular populations: – Pygmy bushmen in Africa, Aboriginals in Australia who have evolved superior eye-sight to Europeans, High altitude respiratory adaptations of endemic populations in the high Himalayas and high Andes, considerable aquatic capabilities in some Pacific island populations, skin colour according to levels of solar radiation at different latitudes.

    Models of human evolution
    Today, all humans are classified as belonging to the species Homo sapiens and sub-species Homo sapiens sapiens. However, this is not the first species of homininae: the first species of genus Homo, Homo habilis, are theorized to have evolved in East Africa at least 2 million years ago, and members of this species populated different parts of Africa in a relatively short time. Homo erectus is theorized to have evolved more than 1.8 million years ago, and by 1.5 million years ago had spread throughout Europe and Asia. Virtually all physical anthropologists agree that Archaic Homo sapiens (A group including the possible species H. heidelgergensis, H. rhodesiensis and H. neanderthalensis) evolved out of African Homo erectus ((sensu lato) or Homo ergaster).[51][52]

    Today anthropologists increasingly believe that anatomically modern humans (Homo sapiens sapiens) evolved in North or East Africa from H. heidelbergensis and then migrated out of Africa, mixing with and replacing H. heidelbergensis and H. neanderthalensis populations throughout Europe and Asia, and H. rhodesiensis populations in Sub-Saharan Africa (a combination of the Out of Africa and Multiregional models)

    In the ancient past hominids did speciate. There are various models of how this could have happened.

    http://ngm.nationalgeographic.com/2011/08/malapa-fossils/lineage-graphic

    If remote extra-terrestrial colonies of humans are established, they will undoubtedly speciate over time if they are isolated from Earth based populations.



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  • 11
    godzillatemple says:

    Thanks for all the thoughtful answers so far! As I said up front, there may be no definitive answer to my question, but I enjoy exploring the possibilities.

    I guess one of the problems is how we actually define “species” in the first place. I’ve been going off the dictionary definition (“related individuals that resemble one another, are able to breed among themselves, but are not able to breed with members of another species”), but I’m assuming that definition was created long before we had the ability to analyze the genetic structure of different species. And, as I mentioned earlier, I’ve always been a bit troubled by the whole “are not able to breed with members of another species” bit, since there seems to be a blurry line between “cannot” (i.e., due to genetic incompatibility) and simply “do not” (i.e., because of sexual preferences) when it comes to interbreeding.

    Is this definition of species even still relevant today? Or do biologists now analyze the genetic structures and say that two groups of related individuals that resemble one another are actually different species if they are X% different genetically, regardless of whether they can or do interbreed?

    In reply to #2 by Red Dog:

    Racial differences are primarily a social construction. From a biological standpoint the slight differences in skin pigment, hair texture, and a few other traits are minimal.

    I was really hoping to avoid that particular argument, since I agree that today, at least, there has been so much intermingling that it’s really hard (if not impossible) to have clear-cut racial distinctions. But it seems clear (to me, at least), that the “slight differences” we see in things like skin pigment and the existence of an epicanthic fold (and perhaps even things like hair color and texture) originally evolved due to populations of humans being isolated and separated over long periods of time. Even if you don’t want to talk about “races” to describe these differences, I believe it still holds true that these differences are the result of natural selection acting on separated populations over time.

    As for whether these “slight differences” are minimal from a biological standpoint, that’s where I’m having the most trouble. As I mentioned, it seems that slight differences such as these are enough to prevent related individuals that resemble one another from actually interbreeding. Looking at all the various species of sparrows, for example, it seems that the variations between the different species are primarily down to coloration patterns (I am not a biologist, of course, and fully acknowledge that the differences might actually be far more significant that what I can personally observe).

    One of my hypothesis was that the sort of changes we see between previously isolated populations of humans would be enough to cause speciation if they occurred in lower order animals, but our intelligence allows us to choose to ignore these differences. A sparrow, for example, might see another sparrow with a white breast feather instead of a brown one and be “unable” to mate with that sparrow as a result (even though they might still be genetically compatible). Humans, however, have enough intelligence to realize that small things like that don’t really matter and therefore are able to keep interbreeding as long as the genetic compatibility remains. I’m not really comfortable with this hypothesis (or the implications of it, at least), since it might lead people to claim that the different races actually are separate species. But that’s why I was asking whether species can be defined based on genetic similarity instead of whether members of one population can (and do) interbreed with members of another population.



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  • 12
    crookedshoes says:

    Look at Richard’s awesome book “The Magic of Reality”. He does an expert job of describing the following (and I am going to do a poor job of relating his words)….

    Imagine a photo of yourself with a photo of your mom behind it and a photo of her mom behind it and so on so on so on… Put 80,000 of these photos in sequence. It would be a heck of a long series of photos… Richard’s work describes it very well…

    Now, pick two pictures. If the two pictures are adjacent, you will not see much difference. However, if the two photos selected are far apart in the stack, they might look dramatically different… So different, in fact that at some point they may be considered different enough from one another to be different species.

    I’ll add my (probably stupid) two cents:

    Would you have sex with someone from Jesus’ time? Think of them, hygiene wise… Think of their teeth, their smell, their habits…. Would you have sex with someone from 5,000 years earlier? 5,000 years earlier? etc etc…

    The hinge to being the same species IS reproduction. So, we categorize species as groups that can interbreed and produce fertile offspring. BUT, a modern human would at some point not WANT to have intercourse with an ancient human (and, I am sure, vice versa). So, even though they “could” produce a baby, they might not because they are (for various reasons) repellant to each other. (This has been demonstrated in Drosophilia that have been raised on different sugar sources… they “smell” different from each other and as a result will not interbreed even though they could)

    This would be the first step towards speciation. You have to imagine the modern and the ancient being contemporaries….



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  • 13
    crookedshoes says:

    Plus, speciation takes selection pressure and genetic isolation. Niether has mounted enough in the modern human world to cause the human branch to further branch…..yet.



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  • 14
    godzillatemple says:

    In reply to #9 by Alan4discussion:

    Only this quickly with organisms (such as bacteria) with short breeding cycles.

    What about this study showing how lizards can undergo rapid evolution after introduction to a new home? Or would those changes not rise to the level of speciation? I don’t think the scientists tried reintroducing the two groups to each other to see whether they could/would interbreed, so perhaps it’s not possible to say.

    Human populations are simply too mobile for populations to be isolated for long enough for the process to progress in separating sections of the gene pool.

    I get that. I guess it all just depends on how long is “long enough.” According to what I’ve been reading, recent genetic studies have shown that modern Aboriginal Australians are the direct descendants of migrants who arrived around 50,000 years ago (and who were presumably isolated during that period). 50,000 years isn’t long enough?



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  • 15
    Alan4discussion says:

    In reply to #13 by godzillatemple:

    In reply to #9 by Alan4discussion:

    I get that. I guess it all just depends on how long is “long enough.” According to what I’ve been reading, recent genetic studies have shown that modern Aboriginal Australians are the direct descendants of migrants who arrived around 50,000 years ago (and who were presumably isolated during that period). 50,000 years isn’t long enough?

    It’s long enough to produce diversity and variation, but Aboriginals are largely being re-absorbed into the larger human gene-pool at present, because of population mobility.

    The point I was making, is that humans are very much at the slow end of reproductive rates, as far as potential for selection goes.

    We take a relatively long time to mature, and then produce relatively few offspring, (even compared to other vertebrates like fish which produce hundreds of eggs, or Octopus which produce thousands of eggs, – all within within a year or two.).

    What about this study showing how lizards can undergo rapid evolution after introduction to a new home? Or would those changes not rise to the level of speciation? I don’t think the scientists tried reintroducing the two groups to each other to see whether they could/would interbreed, so perhaps it’s not possible to say.

    Th cladistics of classification are inexact, so the level of “splitting” is rather subjective and much debated by botanists and zoologists. Evolution is on-going, so this often raises the question,
    “Where do you draw a line on a continuum?” (Ring species From Wikipedia,)

    In other scientific disciplines, new ideas elbowing out old ones is a normal and essential process. But in taxonomy, renewal poses a special problem: how can you replace plant and animal names used for two-and-a-half centuries without causing chaos?

    “If we did not have a system of classification that was hierarchical and had names that could be easily retrieved we would be helpless,” American biologist Edward O. Wilson explained in an interview.

    Taxonomists themselves can poke fun at their sometimes arcane bickering as to whether a new discovery is a species in its own right or a subset of one already on the books.

    “We have ‘lumpers’ and ‘splitters’,” said Richard Pyle, a zoologist and fish specialist at the Bishop Museum in Hawaii, and an officer in the International Commission on Zoological Nomenclature (ICZN).

    “Splitters want to draw the lines around a specimen tightly, while lumpers will say, ‘no, that’s just a slight variation’. And there is nothing in this system which tells you who is right — it is purely subjective,” he said.

    http://www.google.com/hostednews/afp/article/ALeqM5gTyYqm3oZg5EHmdtdUl-qjf-1pEQ

    For example, lions and tigers are quite capable of inter-breeding, but are too geographically separated at present to do so in the wild, so are regarded as separate species.



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  • 16
    Kwwebbo says:

    Referring back to a comment made by Richard, when making the Darwin ‘Origin of the Species’ documentaries. He stated that due to the minimal variances in the DNA makeup of H Sapien and certain species of apes, it may well be possible, in theory I may add, for a human to bread with a certain species of ape. Clearly that is not something that should be pursued on moral grounds at the very least, however the point is that the degree of separation between our H Sapien species in terms of DNA and other closely related species is minimal in the grand scheme of things. On that note it would seem we are acknowledging that what makes a different species is based on the degree of difference!!



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  • 17
    Fixator says:

    Referring back to a comment made by Richard, when making the Darwin ‘Origin of the Species’ documentaries. He stated that due to the minimal variances in the DNA makeup of H Sapien and certain species of apes, it may well be possible, in theory I may add, for a human to bread with a certain species of ape. Clearly that is not something that should be pursued on moral grounds at the very least, however the point is that the degree of separation between our H Sapien species in terms of DNA and other closely related species is minimal in the grand scheme of things. On that note it would seem we are acknowledging that what makes a different species is based on the degree of difference!!



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  • 18
    godzillatemple says:

    In reply to #14 by Alan4discussion:

    For example, lions and tigers are quite capable of inter-breeding, but are too geographically separated at present to do so in the wild, so are regarded as separate species.

    Ah. I was actually thinking of mentioning lions and tigers (and ligers and tigons) and the fact that they can produce fertile offspring. But my post was already waaaaay too long…

    Perhaps I’m simply asking the wrong question. Perhaps the question is not “why humans haven’t speciated” but instead “why do we call some populations different species despite the fact that they are genetically compatible and can interbreed”?

    Let me re-ask a question I posed earlier, though. Is there any current definition of species that relies on genetic differences as opposed to breeding habits to distinguish between related individuals that resemble one another?



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  • 19
    godzillatemple says:

    In reply to #15 by Kwwebbo:

    It may well be possible, in theory I may add, for a human to breed with a certain species of ape.

    Man, that is one road I absolutely do not want to go down! The last thing I want to argue is that any population of humanity could possibly be “less than human” despite the fact that we can all interbreed. My main question is simply why, given tens of thousands of years of isolated populations (in some case, at least), humanity didn’t diverge sufficiently to be considered separate species.



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  • 20
    crookedshoes says:

    I think that the “species concept” is useful but has to be very flexible. The definition that we apply to animals about “interbreeding and making fertile offspring” (which is where the tiger lion example breaks down)… does not transfer well to identifying species of bacteria.

    Is there any current definition of species that relies on genetic differences as opposed to breeding habits to distinguish between related individuals that resemble one another?

    Your question about genetics and sequences defining species is (IMO) more applicable to prokaryotes where the “lines” are much more blurry.

    In reply to #16 by godzillatemple:

    In reply to #14 by Alan4discussion:

    For example, lions and tigers are quite capable of inter-breeding, but are too geographically separated at present to do so in the wild, so are regarded as separate species.

    Ah. I was actually thinking of mentioning lions and tigers (and ligers and tigons) and…



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  • 21
    Red Dog says:

    In reply to #16 by godzillatemple:

    Perhaps I’m simply asking the wrong question. Perhaps the question is not “why humans haven’t speciated” but instead “why do we call some populations different species despite the fact that they are genetically compatible and can interbreed”?

    Here is one of my favorite Dawkins essays:

    Gaps in the Mind

    It deals with issues about species and how the concept of a species isn’t always something that has rigorous unambiguous boundaries.



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  • 22
    godzillatemple says:

    In reply to #18 by crookedshoes:

    Your question about genetics and sequences defining species is (IMO) more applicable to prokaryotes where the “lines” are much more blurry.

    That whooshing sound you may have just heard was your comment passing over my head… I’ll have to look up prokaryotes and get back to you.

    I am assuming that it is possible to detect genetic differences between human populations. I realize I shouldn’t get my information from pop culture, but there was that recent case of a self-identified “white supremacist” who was informed that a DNA analysis showed he was actually 86% “European” and 14% “Sub-Saharan African”. Presumably, that means there are genetic differences between the two populations. I’m guessing the percent difference, however, is extremely small (0.01%? 0.001%? Smaller?). So my question is whether it is possible to define different species as being more than X% different genetically so as to avoid the need to talk about whether they can, do or would interbreed?



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  • 24
    Red Dog says:

    In reply to #21 by godzillatemple:

    In reply to #19 by Red Dog:

    Here is one of my favorite Dawkins essays:

    Just finished reading that. Thank you very much for sharing it!

    Glad you liked it. FYI, there is another version of it (where I first read it) in the excellent Dawkins book A Devil’s Chaplain. After Selfish Gene and God Delusion that one is my favorite Dawkins book and one you might want to add to your reading list. It’s a collection of essays that are all very insightful and fun to read.



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  • 25
    Kwwebbo says:

    Sorry guys but I’m asking more questions than I’m attempting to answer:-
    Here’s a another hypothetical question that will undoubtedly conjure up other questions. Is there any evidence to date based on genetic research of the human species to suggest that we have a dominant area within our DNA structure that inhibits the change of our basic biological make-up? On that basis are H Sapiens less susceptible to species variance over time and influence of environment, than other non human species?



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  • 26
    Fixator says:

    Sorry guys but I’m asking more questions than I’m attempting to answer:-
    Here’s a another hypothetical question that will undoubtedly conjure up other questions. Is there any evidence to date based on genetic research of the human species to suggest that we have a dominant area within our DNA structure that inhibits the change of our basic biological make-up? On that basis are H Sapiens less susceptible to species variance over time and influence of environment, than other non human species?



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  • First, we are a very new species. We have not had time to split.
    Second, our transportation technology keeps stirring the gene pool. For speciation you need geographical isolation.
    At this point, natural selection is being supplanted by gene technology. Future changes in the structure of humans will be a result of intelligent design.



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  • There are many species of cetacea (dolphins and whales). Dolphins like to breed with anything with a suitably sized hole, including humans. They have been around much longer than we have.



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  • 29
    godzillatemple says:

    In reply to #24 by Roedy:

    Our transportation technology keeps stirring the gene pool. For speciation you need geographical isolation.

    Well, that is certainly true today, and as a result the odds of humanity ever speciating in the future is probably pretty remote (unless and until we start colonizing other planets). That has not always been the case, however, and separate populations of humanity have been geographically isolated for up to 50,000 years (in the case of Aboriginal Australians). If the answer is simply that 50,000 years is not enough time to speciate, I guess that’s the end of the discussion. Once again, however, from what I’ve read speciation can happen in much shorter time frames.



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  • In reply to #5 by Seraphor:

    domestic dogs

    I would think chihuahuas and great Danes could not interbreed for purely physical reasons. Presuming this is true, would they be considered a separate species?



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  • defining a species

    Perhaps you could define a species by looking at the DNA. A species has a basic block of common DNA. If you are proposing a second species it too must have a common block of DNA, that only partially overlaps with the first species. If the individuals in the second group different in a random way from the first, they are not a species. This is just a rough cut at the idea. The idea is species definition should be based on percent common DNA.



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  • 32
    godzillatemple says:

    In reply to #22 by Red Dog:

    Glad you liked it. FYI, there is another version of it (where I first read it) in the excellent Dawkins book A Devil’s Chaplain. After Selfish Gene and God Delusion that one is my favorite Dawkins book and one you might want to add to your reading list. It’s a collection of essays that are all very insightful and fun to read.

    I’ll have to add “A Devil’s Chaplain” to my queue, thanks. I haven’t bothered with “The God Delusion” since I’m already an atheist… ;^)



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  • In reply to #23 by Kwwebbo:

    Sorry guys but I’m asking more questions than I’m attempting to answer:-
    Here’s a another hypothetical question that will undoubtedly conjure up other questions. Is there any evidence to date based on genetic research of the human species to suggest that we have a dominant area within our DNA struct…

    Compared with retroviruses we are more resistant to mutation. They use RNA instead of DNA. DNA is far less likely to make errors. I read many years ago that cockroach DNA is highly resistant to mutation. If that is true, we might exploit how they do it to prevent cancer.



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  • 34
    Alan4discussion says:

    In reply to #16 by godzillatemple:

    In reply to #14 by Alan4discussion:

    Let me re-ask a question I posed earlier, though. Is there any current definition of species that relies on genetic differences as opposed to breeding habits to distinguish between related individuals that resemble one another?

    That is one of the current problems which is in transition.

    The traditional Linnaean taxonomy is gradually giving way to genetically based classification, but there are millions of species and this all takes time.

    The old system works on comparing physical (phenotypic) features, leads to problems with convergent or parallel evolution – especially in closely related species, which may even look physically identical, while being unable to breed due to genetic differences.

    A botanist friend of mine doing field-work, keeps finding visually similar plants from a wide geographical spread, “lumped” under the same species or genus name, but which are much more distantly related when DNA sampling is done.

    Conversely there are species which have been “split” into different species, which are shown by genetics to be only forms, variations or sub-species.

    It would cause chaos to scrap the old system before the new ones cover the extensive range or organisms – but scientists are working on it.

    DNA barcoding

    DNA barcoding is a taxonomic method that uses a short genetic marker in an organism’s DNA to identify it as belonging to a particular species.[1] It differs from molecular phylogeny in that the main goal is not to determine patterns of relationship but to identify an unknown sample in terms of a preexisting classification.[2] Although barcodes are sometimes used in an effort to identify unknown species or assess whether species should be combined or separated,[3] the utility of DNA barcoding for these purposes is subject to debate.[4] The most commonly used barcode region, for animals, at least, is a segment of approximately 600 base pairs of the mitochondrial gene cytochrome oxidase I (COI).

    Applications include, for example, identifying plant leaves even when flowers or fruit are not available, identifying insect larvae (which may have fewer diagnostic characters than adults and are frequently less well-known), identifying the diet of an animal, based on its stomach contents or faeces[5] and identifying products in commerce (for example, herbal supplements or wood).

    The whole system is rather complicated if you are not familiar with it:-

    International Code of Zoological Nomenclature

    International Code of Nomenclature for algae, fungi, and plants

    …and the botanists and zoologists use different systems!



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  • 35
    Mr Greene says:

    In reply to #26 by godzillatemple:

    In reply to #24 by Roedy:

    Our transportation technology keeps stirring the gene pool. For speciation you need geographical isolation.

    Well, that is certainly true today, and as a result the odds of humanity ever speciating in the future is probably pretty remote (unless and until we start colonizing other planets). That has not always been the case, however, and separate populations of humanity have been geographically isolated for up to 50,000 years (in the case of Aboriginal Australians). If the answer is simply that 50,000 years is not enough time to speciate, I guess that’s the end of the discussion. Once again, however, from what I’ve read speciation can happen in much shorter time frames…

    It isn’t so much a question of time as of the number of generations during which a population has been isolated.
    The period of time required for Homo antecessor to speciate resulting in Homo sapiens was roughly 600,000 years. As such 50,000 years simply doesn’t produce the required number of generations for speciation to occur.



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  • 36
    godzillatemple says:

    In reply to #28 by Roedy:

    The idea is species definition should be based on percent common DNA.

    Yes, that was my proposal. Not sure how workable it is, however. As Seraphor pointed out, speciation may be down to the specific way in which the species have evolved and not necessarily the amount they have evolved. Even if you wanted to look solely at percent common DNA, however, it would still be an arbitrary determination of what percentage constitutes a separate species.



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  • 37
    Alan4discussion says:

    In reply to #16 by godzillatemple:

    In reply to #14 by Alan4discussion:

    Perhaps I’m simply asking the wrong question. Perhaps the question is not “why humans haven’t speciated” but instead “why do we call some populations different species despite the fact that they are genetically compatible and can interbreed”?

    Usually it is because they are geographically separated and don’t interbreed in the wild.

    There may be physical problems – like in dogs – why a Miniature Poodle cannot breed with a Great Dane.

    It can get very complicated with plants or species with large numbers of offspring, because while “hybrids” are often sterile, fertility drops off rather than cuts off. Crosses of plants which are not evolved quite far enough along their evolutionary branch to produce totally sterile hybrids or no fertile seed at all, can produce a small percentage of fertile hybrid seeds. As I was saying it can be the question of drawing a boundary line on a continuum.

    Evolved speciating branches with a clear gap between them are easy to understand. Ring or line species with existing intermediates, present a much more complicated picture.

    We should always remember that a species is a gene-pool with diversity, and not an individual organism. Individual organisms only contain a part of the species genome.



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  • 38
    godzillatemple says:

    In reply to #32 by Mr Greene:

    It isn’t so much a question of time as of the number of generations during which a population has been isolated. The period of time required for Homo antecessor to speciate resulting in Homo sapiens was roughly 600,000 years. As such 50,000 years simply doesn’t produce the required number of generations for speciation to occur.

    Well, I’m still not convinced that 50,000 years “simply doesn’t produce the required number of generations for speciation to occur,” at least not in general. Even assuming a modest 20 years per generation, that’s still 2500 generations. Annnnnnd…. you’re probably right. Putting it that way, 2500 generations doesn’t really seem like enough time for much to happen after all.

    Except, do we have evidence of other higher level organisms (not talking bacteria here) evolving into separate species within 2500 generations? I thought we did, but perhaps not. Assuming we do, we’d have to explore what prevented it from happening with humans. One thing I didn’t consider explicitly but which has been pointed out is that our ability to adapt our environment to ourselves (instead of the other way around) may well have blunted the effects of natural selection on us so that only minor variations occurred.



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  • 39
    godzillatemple says:

    In reply to #34 by Alan4discussion:

    There may be physical problems – like in dogs – why a Miniature Poodle cannot breed with a Great Dane.

    Wait. That doesn’t mean they are considered different species, though, right?



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  • Given the propensity for global travel of the modern human, I don’t think we’ll ever see the sort of isolation faced by the Australian Aboriginal population or the Bushmen of the Kalahari. Perhaps if a human colony were to be established on Mars and a cataclysmic event made it impossible to reach home we’d see a different species emerge. ( lot of hurdles in that scenario ).

    The fact that traces of Neanderthal DNA exist ( and other subspecies) indicates that huge differences need to occur before offspring of the mix become infertile.



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  • 41
    godzillatemple says:

    In reply to #37 by Nitya:

    Given the propensity for global travel of the modern human, I don’t think we’ll ever see the sort of isolation faced by the Australian Aboriginal population or the Bushmen of the Kalahari.

    I don’t think anybody is disputing that. The question is, given the sort of isolation already faced by the Australian Aboriginal population or the Bushmen of the Kalahari in the past, why didn’t they evolve into separate species.

    The general answer seems to be simply that they weren’t isolated long enough. I can accept that, but I still wonder whether there were some other inhibiting factors at work. Perhaps, as suggested, the fact that humans had already evolved to the point where they could manipulate their environment to a great degree (creating shelter, make fire, wear clothing, etc.) kept these populations from being affected by natural selection more radically. Obviously, natural selection had some varying effect on the different populations, or else there wouldn’t be any differences at all between them. But not enough of an effect, however, to prevent interbreeding (or, as I’ve been arguing, to cause sufficient genetic variation to be considered a separate species).

    Again, the question isn’t whether we are all members of the same species [we are] or whether we might someday diverge into separate species in the distant future [probably not]. The question is why we are all still members of the same species given the past instances of isolated populations in dramatically different environments — apparently the same circumstances which have caused speciation in other organisms.



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  • In reply to #38 by godzillatemple:

    In reply to #37 by Nitya:

    Given the propensity for global travel of the modern human, I don’t think we’ll ever see the sort of isolation faced by the Australian Aboriginal population or the Bushmen of the Kalahari.

    I don’t think anybody is disputing that. The question is, given the sort of isolat…

    What if…….just speculating here, I’m sure someone will correct me…. the Australian continent supported a lethal virus that killed off every other human before reproductive age? Let’s say that the aboriginal population possessed a gene that made them immune to the effects of this virus. Given enough time, would they develop into another species? ( this hitherto unknown gene could piggyback on some other distinctly aboriginal characteristic).



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  • 43
    Alan4discussion says:

    In reply to #36 by godzillatemple:

    In reply to #34 by Alan4discussion:

    There may be physical problems – like in dogs – why a Miniature Poodle cannot breed with a Great Dane.

    Wait. That doesn’t mean they are considered different species, though, right?

    They are not genetically different species, but would have the potential to develop into different species, if the intermediate sizes in populations linking them became extinct – or in this case human selectors keeping them separate. This sort of thing happens with predators. If it was terriers rather than poodles, on an island where only burrowing prey lived, there could be selection pressure against big dogs which could not get into the holes. On another island with big defensive prey small dogs would be eliminated.

    It is these sorts of isolated islands which generate unique species from the few organisms which reach their shores.

    (see Galapagos, tree kangaroos, Komodo Dragons, flightless birds, Land Crabs etc)



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  • 44
    crookedshoes says:

    Just to clarify a pedantic point. Speciation can occur under different circumstances. One set of circumstances is given the name allopatric speciation and another type is called sympatric speciation. Geographic isolation is a requirement for allopatric speciation but is not required for sympatric speciation.



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  • 45
    crookedshoes says:

    The dog example is a bit more complicated and a couple points should be raised about the situation.
    The breeds of dogs are really “sub species”. They are like “races” of humans. i put them in quotes because they are constructs that are typically meaningless genetically. However, the dog example brings to light a really cool concept: ring species.

    If you think of the dog breeds in terms of ring species and THEN geographically isolate the mini poodle from the great dane, they could develop into different species, especially if all other breeds are somehow eliminated.



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  • 46
    crookedshoes says:

    Nitya,
    Look up adaptive radiation (my explanation will pale in comparison to a good text or wiki reading). The area vacated by the “dead Australians” would now be open to the immune Bushmen. The new environment might spur changes and allow for the evolution of the immune bushmen!

    In reply to #39 by Nitya:

    In reply to #38 by godzillatemple:

    In reply to #37 by Nitya:

    Given the propensity for global travel of the modern human, I don’t think we’ll ever see the sort of isolation faced by the Australian Aboriginal population or the Bushmen of the Kalahari.

    I don’t think anybody is disputing that. The q…



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  • In reply to #43 by crookedshoes:

    Nitya,
    Look up adaptive radiation (my explanation will pale in comparison to a good text or wiki reading). The area vacated by the “dead Australians” would now be open to the immune Bushmen. The new environment might spur changes and allow for the evolution of the immune bushmen!

    In reply to #39…

    Ok, thanks. I’ve been waiting patiently for an answer because it seemed logical to me, but maybe I wasn’t seeing the problem clearly.
    To my way of thinking, the aboriginals ( of my imaginings) would have found a niche that was inhospitable to all other types of human as opposed to just physical isolation.



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  • 48
    Alan4discussion says:

    In reply to #42 by crookedshoes:

    If you think of the dog breeds in terms of ring species and THEN geographically isolate the mini poodle from the great dane, they could develop into different species, especially if all other breeds are somehow eliminated.

    http://en.wikipedia.org/wiki/Canid-hybrid#Canid-interfertility-chart

    Interestingly we were discussing dog evolution, fertility and breeding here:- http://www.www.richarddawkins.net/news-articles/2013/11/16/first-fido-dna-study-points-to-europe-as-place-where-wolves-evolved-into-man-s-best-friend#



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  • 50
    crookedshoes says:

    Also, the experiments that began in the 1950’s and continue to this day regarding domestication of silver foxes and fleeing distance have always been so so so fascinating to me. The researcher who go it going was Dmitri Belyaev and his work is remarkable.

    Everyone here who is unfamiliar should google and read. It is just the most unbelievable stuff. I am talking artificial selection at it’s finest.



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  • Define species

    I had the naive notion two similar populations were different species if they could not interbreed, or if they had a different number of chromosomes. It sounds like the definition is a lot squishier than that. Could anyone please define species?



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  • In reply to #47 by crookedshoes:

    Also, the experiments that began in the 1950’s and continue to this day regarding domestication of silver foxes and fleeing distance have always been so so so fascinating to me. The researcher who go it going was Dmitri Belyaev and his work is remarkable.

    Was that the guy who created a creature that behaved like dog but looked like a fox?

    I saw a fox on a walk down a lane in England. It was such a beautiful graceful creature. I could see the appeal as pets.



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  • In reply to #41 by crookedshoes:

    Just to clarify a pedantic point. Speciation can occur under different circumstances. One set of circumstances is given the name allopatric speciation and another type is called sympatric speciation. Geographic isolation is a requirement for allopatric speciation but is not required for sympatric.

    Allopatric means, according to WikiPedia, speciation by geographic split. Sympatric means speciation when both species live in the same area, presumably specialising on two different food sources or nesting sites or the like.



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  • 54
    Pauly01 says:

    My opinion

    The human brain has slowed down natural selection. Our wit and intelligence has by passed natural selection for the large part.

    Think about it:)



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  • 55
    CdnMacAtheist says:

    Another reason that Homo sapiens hasn’t speciated is that due to relatively recent population bottlenecks our species is quite homogeneous.
    If our ancestors had been more numerous and spread to (say) the Americas or Australia millions of years ago, there probably would be separate species by now, even within continents due to distance, terrain and climate variation – ie: north vs south America or inland vs coastal Australia. Browse ‘Homo sapien population bottlenecks’ for links:

    http://www.scientificamerican.com/article.cfm?id=humans-might-have-faced-extinction

    http://whyevolutionistrue.wordpress.com/2011/09/18/how-big-was-the-human-population-bottleneck-not-anything-close-to-2/

    From link 2: “All the data clearly show that all modern humans, African and non-African alike, descend from one ‘homogeneous ancestral population in the last 100,000 years, with subsequent minor admixture out of Africa from Neanderthals’.”



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  • 56
    Alan4discussion says:

    Another feature which may restrict human speciation is inter-tribal competition and genocide. That seems to have eliminated the Neanderthals, and more recently various remote tribes over-run by invaders.



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  • 57
    yanquetino says:

    In reply to #1 by masubi:

    You and your wife are not “entirely different races.” There is only one race of humans, the human race. Different “races” would be equivalent to “subspecies.” There were several different races (subspecies) of Darwin’s finches…different species.

    Mmmm. I don’t know about that. It would depend upon one’s definition of “race.” And godzillatemple admittedly used the term cautiously. Traditional interpretation is that there evolved five different races of Homo sapiens: australoid, caucasoid, capoid, congoide, and mongoloid. I suppose that, in my mind, those races are similar to “breeds” in other animals. They each have general physical characteristics within the group that distinguish them from the other groups, and were obviously the result of geographic isolation over millenia.

    They are by no means separate species, of course, because we can all interbreed with one another. The geographic isolation simply did not last long enough for that to happen. Indeed, because these “breeds” are no longer isolated, and can now move freely throughout the entire world, Homo sapiens seems to be evolving into what José Vasconcelos deemed a cosmic race, in which the genes for what used to be distinguishing characteristics are being shuffled together into an amalgam of physical appearances. Tongue-in-cheek, perhaps we could postulate that, after a few more centuries, all Homo sapiens will become a “Heinz 57 race”…?



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  • 59
    Ospreywing says:

    I think modern biologists consider all so-called “races” of humans to be one species because the genetic variations within “races” are greater than the variations between races. If true species differences existed, genetic variations would be greater between “races” than within them.
    Race is simply a sociological construct, and not a very useful one at that.



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  • 60
    crookedshoes says:

    Roedy, there are over 20 current definitions. I hate when things are more complicated than they need to be. But, this is a very “man made” label and as such, it does not fit every situation with the same functionality.

    What I mean is, if you work with animals, the species definition that works is the “interbreeding individuals that can make fertile offspring” kind of definition. However, this does not work with asexual organisms like bacteria. Also, plants readily hybridize and it is not all that satisfactory for many plant folks.

    Look at how crazy it gets @ :
    http://scienceblogs.com/evolvingthoughts/2006/10/01/a-list-of-26-species-concepts/

    I guess this is one of those “continuous mind” vs. “discontinuous mind” issues….
    In reply to #48 by Roedy:

    Define species

    I had the naive notion two similar populations were different species if they could not interbreed, or if they had a different number of chromosomes. It sounds like the definition is a lot squishier than that. Could anyone please define species?



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  • 61
    godzillatemple says:

    In reply to #56 by Ospreywing:

    Race is simply a sociological construct, and not a very useful one at that.

    I’m not sure I entirely buy that, to be honest. To me, a purely sociological construct would be if, say, the group of people we call Inuit all had similar physical characteristics because all the people in the world with those characteristics chose to live together. Kind of like social groups in school such as “jocks” or “goths.” If, on the other hand, a group of people share common physical characteristics because those characteristics are the result of natural selection working on them in a way specific to their environment over thousands of years, I think you have to say there is also a genetic component to the concept.

    Having said that, it’s an entirely different discussion as to whether those shared physical characteristics are particularly important or relevant, or whether they are wholly superficial. And the fact that there has been some interbreeding among some of those previously isolated populations doesn’t change the fact that we still have more or less distinct groups of humans who have evolved distinct, albeit, superficial physical characteristics. Granted, as time goes on and interbreeding continues, those distinctions will probably become less and less evident.



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  • 62
    Ospreywing says:

    To godzillatemple,
    The greater difference in genetic diversity within, than between, human populations is a scientific fact that has been replicated by many studies. Richard Lewontin was one of the first to show that about 85% of genetic differences was found within human populations. About 7% differentiated between populations within a “race” (e.g. Swedes vs. Greeks) and only about 8% was found to differentiate between human races. Lewontin and many others concluded that subspecies classification should be scrapped. Most biologists take this position today.

    So what is the point of continuing to find ways to divide the human species into subgroups of various kinds: genetic, morphological, behavioral, psychological,cultural, etc? It seems to me that recognizing our common humanity will do much more good than emphasizing any differences that may exist.



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  • 63
    crookedshoes says:

    Ospreywing,
    I was teaching a very diverse group of advanced biology students just this past week. We were talking about Mendelian genetics and the ideas of hair eye and skin color (as always) came up. I always tie things to evolution because it is covered last in my course sequence I talk about the entire time. Anyway, I was saying that with the amount of interbreeding that is going on and that (at last!) societal acceptance of it, we could look forward to a day when we were all the same color of “tan”…

    One of my most inspiring students (who happens to be African American) said “YAY!!!”

    I looked at him and said “Son, don’t think that human beings won’t find another reason to hate one another”… So so so sad.

    In reply to #59 by Ospreywing:

    To godzillatemple,
    The greater difference in genetic diversity within, than between, human populations is a scientific fact that has been replicated by many studies. Richard Lewontin was one of the first to show that about 85% of genetic differences was found within human populations. About 7% diffe…



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  • 64
    ShadowMind says:

    I read somewhere recently (I would provide a link, but I can’t for the life of me remember where…) that the human race as a whole has incredibly low genetic diversity. So that, while there have been long-term isolated populations, and there are (obviously) a range of physical differences, at a genetic level those differences are so tiny that they aren’t enough to create speciation.

    Also, re: defining “species”, if two species that are defined as such due to “other” things such as geographical separation, but can be successfully interbred; what species is the offspring?



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  • 65
    CdnMacAtheist says:

    In reply to #61 by ShadowMind:

    Also, re: defining “species”, if two species that are defined as such due to “other” things such as geographical separation, but can be successfully interbred; what species is the offspring?

    Taking the case of Ligers and Tigons, which can still have (not too successful) offspring with their own sub-names, those species separated 2 – 4 mya, so human ‘races’ would have needed a very long time completely apart to totally speciate, as I mentioned in my earlier comment #52.

    http://www.pbs.org/wgbh/evolution/library/05/2/l_052_02.html

    http://en.wikipedia.org/wiki/Panthera



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  • 66
    ShadowMind says:

    In reply to #62 by CdnMacAtheist:

    I appreciate that. What I meant was, if a tiger (Panthera tigris) and a lion (Panthera leo) have an offspring, it would be a Panthera what?



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  • 67
    CdnMacAtheist says:

    In reply to #63 by ShadowMind:

    In reply to #62 by CdnMacAtheist:

    I appreciate that. What I meant was, if a tiger (Panthera tigris) and a lion (Panthera leo) have an offspring, it would be a Panthera what?

    Hi SM.

    First, I see that my 1st link doesn’t work properly for some reason – it is:

    http://www.pbs.org/wgbh/evolution/library/05/2/l_052_02.html
    (There are underscores between 1&0 and between 2&0 – I don’t understand why that shows in the comment I write but not when it’s posted!!!)

    Also, the species names of hybrids are not given, since they aren’t really viable as species, just as short hybrid tangents. I do see their hybrid names running through various links – Liger, Ligress, Tigon, Tiglon, Taliger, Litigon, Liliger, Pumapard, Leopon, etc.

    http://en.wikipedia.org/wiki/Category:Panthera_hybrids

    If you browse ‘What species are Ligers & Tigons’ then you’ll find some links that explain various aspects of the question…. Mac.



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  • 69
    Red Dog says:

    In reply to #64 by CdnMacAtheist:

    There are underscores between 1&0 and between 2&0 – I don’t understand why that shows in the comment I write but not when it’s posted!

    It’s a bug (or feature depending on your point of view) of the rd.net commenting system. It interprets underscores as markup, as not being part of the text but rather as a signal to the system to start emphasizing what comes after the underscore. So as it processes the text it removes the underscore. The best way is to just make it an actual link. I can’t give you an example of how to do that because the system will think I’m trying to make a link and you won’t see the actual chars you need to type but all you do is put the text you want displayed in brackets and then the link right next to it (no space that’s important) in parentheses. Click on the “Help with formatting click here” link underneath the comment box and it will explain. It’s easier than it sounds.



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  • 70
    Alan4discussion says:

    In reply to #64 by CdnMacAtheist:

    First, I see that my 1st link doesn’t work properly for some reason – it is:

    (There are underscores between 1&0 and between 2&0

    http://www.pbs.org/wgbh/evolution/library/05/2/l-052-02.html

    The underscores are not shown but have converted your “0”s to italic. I have replaced the underscores with – (dashes) in the visible link within the [] brackets, but put the underscores in correctly in the unseen follow-on ( ) brackets which activate the link. (& also creates problems when editing)

    Another example of a breakdown of species boundaries is the Scottish wild cat, which is in danger of extinction in the pure species form, because of cross breeding with feral domestic cats.

    There is a similar situation with Ruddy Ducks cross breeding with other duck species.

    http://www.rspb.org.uk/ourwork/policy/species/nonnative/ruddyducks.aspx
    Ruddy ducks interbreed with white-headed ducks, producing fertile hybrids. This is happening in Spain, and there is a real danger that if the number of ruddy ducks arriving in Spain were allowed to increase, they would inundate the white-headed duck population. As ruddy ducks are more promiscuous in their mating behaviour, the likely result would be a population comprising increasing numbers of hybrids showing fewer characteristics of the white-headed duck, until the species disappears. This has been seen in New Zealand where the introduction of mallards has resulted in the catastrophic decline of the native grey duck due to hybridisation.



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  • 72
    CdnMacAtheist says:

    In reply to #67 by Alan4discussion:

    In reply to #64 by CdnMacAtheist: First, I see that my 1st link doesn’t work properly for some reason.

    A4D: The underscores are not shown but have converted your “0”s to italic.

    Thanks A4D & Red Dog….

    As I’ve said before I’m not computer savvy, type with 2 fingers, and don’t easily follow these things – especially as my last link had an underscore which copied ok – which is why you haven’t seen any ‘blue’ Links in my comments. That proves that there are Neanderthal hybrid bits in my genes, which I’m still trying to culturally overcome…. 😎 Mac.



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  • 73
    bob_e_s says:

    In reply to #52 by CdnMacAtheist:

    Another reason that Homo sapiens hasn’t speciated is that due to relatively recent population bottlenecks our species is quite homogeneous.

    I hope no one else has posted this already, but something like this must be a major player in the lack of human genetic diversity.

    http://en.wikipedia.org/wiki/Toba_catastrophe_theory

    70,000 years ago the entire homo sapiens population may have had as few as 10,000 individuals. That’s the blink of an evolutionary eye, really, isn’t it?



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  • 74
    Malaidas says:

    I am a long time out of the field, having switched from Biochem to Computers so I am 15 years out of date, however I think I have an answer here. Covered roughly in the first page of answers below I think, but I would like to put my own particular thoughts on this as well.

    1) Evolution doesn’t perform to a schedule: It is a matter of rare chance mutations, (this is to all reasonable respects) random, or at least completely unpredictable, to satisfy the purists. It is accelerated by various stress factors/isolation but putting a time scale on it is impossible. It is the factor of natural selection that then drives speciation from this and this requires geological time and selective pressure usually. We as a ‘species’ are only perhaps 100K or so old, which is a tiny amount of time geologically, when you put in to account our reproductive cycle. If we take 20 years even as our generation rate, which is I agree for much of human history, an underestimation, but a nice round figure we get 40,000 generations. Sounds large but when you consider that for a bacterial population, this same generational figure occurs in a little over 9 years on average, the comparison is graphic.

    2) The term species is an artificial concept, brought about by our need to categorise things. Reality is that rather than being such a ‘digital’ system, the journey to speciation is an ‘analogue’ process. It depends completely on the point where 2 separate complexes of genes cannot combine to create a viable organism, rather than upon phenotypical differences. Different ‘Races’ look a bit different, but they are genetically very similar. The differences have not yet moved to the point where incompatibility has occurred

    3) Speciation is a difficult concept to tell anyway where humans are concerned, some human partners might be incompatible and we will never know, not having the right to start testing this

    the truth is that trying to ask why something hasn’t speciated yet is a bit of a fred herring, under usual circumstances speciation doesn;t occur, its a rare event, but over evolutionary history these rare events have added up to create the plethora of life we see today.



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  • 75
    BenCarollo says:

    Well relly it is beause of people like you and your wife, believe it or not human beings are very liberal with their sexual lives and so people actually enjoy different so even though humans spread throughout all of the world we still maintained contact in the sense the europeans still had babies with middle easterns and they still had sex with africans and asians and so eventually asian and african genes got to europe and vice versa so enough indirect interbreeding was happening so that human remained genetically viable candidates with eachother.

    On another note there were indee other human species both previous and during our time as humans and we did do some interbreeding with them, the average person is about 2% neanderthal, so there was indeed speciation in more early human times, for whatever reason though the other types of humans died whether that be due to catastorphe or by the hand of homo sapiens is still up for debate.



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  • 76
    Galaxian says:

    Hi Godzillatemple. You’re perfectly right about the definition of “species”; “My current understanding of “speciation” is that it occurs when two segments of a population diverge sufficiently that the members of the two segments either cannot or do not interbreed.

    Speciation is an area of biology that is not well defined, and is rampant with politics & emotional influence. However, science is the study of pure, untainted knowledge. In other words, an advocate of scientific principles must not be influenced by current fads, fashions, & PC requirements.

    Unfortunately, many people who fancy that they are scientific thinkers are as prejudiced as bigots uneducated in scientific principles. And human races is one such area of erroneous beliefs.

    As Hominins go, there have been, and there are several subspecies or races. Some, such as Neanderthals, Denisovans, and Erectus, are now extinct in their original or “Typical” (specific museum sample) form. Of course, the museum “type” specimen is not the be all & end all of it. There were variations in those human subspecies, as there are in the present human subspecies. Furthermore, there was a degree of interbreeding between them.

    Some of that interbreeding happened between those subspecies and the various Homo sapiens they came in contact with. That’s why current human populations have significant admixtures of the ancient DNA of former subspecies.

    Anyone with half an eye can clearly see that there are human subspecies. When we look into it at a deeper level with modern analytical laboratory techniques, the unbigoted seeker of truth has even more evidence to support human subspeciation. Furthermore, we know that subspeciation and speciation are the natural direction of all organisms, and humans are not exempt from that universal biological law.

    As per your original observation, and the biological definition, there definitely are human populations who, a) Avoid interbreeding, and, b) Whose cross-fertility is higher or lower depending which population they might decide to breed with.

    At the very least, that is evidence of sub-speciation, whether someone accepts it or rejects it.



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  • 77
    Red Dog says:

    In reply to #74 by Galaxian:

    Anyone with half an eye can clearly see that there are human subspecies.

    That is an appeal to common sense not a scientific argument. The reason we have science is because many things that people “clearly see” turn out to be false when analyzed

    When we look into it at a deeper level with modern analytical laboratory techniques, the unbigoted seeker of truth has even more evidence to support human subspeciation.

    Who are these subspecies? If you are implying that they correspond to the way humans typically divide up races, that is wrong.

    As per your original observation, and the biological definition, there definitely are human populations who, a) Avoid interbreeding, and, b) Whose cross-fertility is higher or lower depending which population they might decide to breed with.

    I’m not aware of any human sub-species in that sense among the human species. You have to go back to species such as Neanderthals. Blacks, whites, Hispanics, Asians, can all completely interbreed. To the extent that they haven’t in the past those were for societal rather than biological reasons.

    Race is essentially a vacuous term for a biologist. It’s a few alleles that control things like skin pigmentation and as far as I know no one has ever shown a correlation between those alleles and traits like intelligence. And even if they do at some point so what? It would be like say finding evidence that left handed people are a bit more intelligent on average. Suppose that were true would there be any rational societal implications? Would we start reserving all the best jobs or spots in college for left handed people? Of course not because that kind of data tells you nothing about any specific individual.



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  • 78
    Galaxian says:

    In reply to #16 by godzillatemple:
    >

    Let me re-ask a question I posed earlier, though. Is there any current definition of species that relies on genetic differences as opposed to breeding habits to distinguish between related individuals that resemble one another?

    Unfortunately NO, there is no clear definition of species or subspecies (race). And that is the nub of the problem. Biologists are largely at fault here, because scientists (like most) want to portray that they have a good command of the principles of their profession. So they talk about species & subspecies in a casual, haphazard way. The general public naturally assume that the scientists know what they’re talking about… being specialists in their field.

    But the fact is, that if we approach this from a strictly mathematical standpoint, many organisms that are currently categorized as different species would be reclassified as the same species, or at most merely subspecies (such as the various canines & cats). And some organisms currently classified as one species would be reclassified as different species or subspecies (such as humans).

    The traditional rule has indeed been flawed in that cultural preferences have come into it; such as the avoidance of some birds to plumage of a different color, or some fish to different markings, even though they are quite cross-fertile. thus their prejudices are taken into account. Well, on that account Jews & Muslims should be categorized as different species (they are reluctant to interbreed), eh? 😉



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  • 79
    Galaxian says:

    In reply to #75 by Red Dog:

    Race is essentially a vacuous term for a biologist. It’s a few alleles that control things like skin pigmentation and as far as I know no one has ever shown a correlation between those alleles and traits like intelligence. And even if they do at some point so what? It would be like say finding evidence that left handed people are a bit more intelligent on average. Suppose that were true would there be any rational societal implications? Would we start reserving all the best jobs or spots in college for left handed people? Of course not because that kind of data tells you nothing about any specific individual.

    It’s news to me that subspecies (race) is a vacuous term for a biologist. Furthermore I fail to see why you’ve dragged in the red-herring of “intelligence”. Nowhere in my post did I even vaguely refer to intelligence. And indeed I wouldn’t care if intelligence was selected for in some human subspecies, nor would I respect or disrespect those people of higher or lower intelligence: I’d only be interested in the “content of their character, not their intelligence”, as M.L. King might have said.

    However, since you mention it, Insofar as intelligence is concerned, do you deny that it has to do with the brain? Or do you assert that it has to do with the “soul” (whatever that is, as some do)?

    If you concede that intelligence has to do with the brain, and the brain is a necessary outcome of Natural Selection forces; then, are you stating that ALL parts of the human organism are influenced by Natural Selection, but somehow the brain is quarantined from selection pressures? (No reply required).



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  • 80
    Red Dog says:

    In reply to #77 by Galaxian:

    In reply to #75 by Red Dog:

    Race is essentially a vacuous term for a biologist. It’s a few alleles that control things like skin pigmentation and as far as I know no one has ever shown a correlation between those alleles and traits like intelligence. And even if they do at some point so what? It wo…

    You ignored my questions. In your previous comment you said:

    there definitely are human populations who, a) Avoid interbreeding, and, b) Whose cross-fertility is higher or lower depending which population they might decide to breed with.

    I say that is bullshit and challenge you to come up with some examples of human populations that can’t interbreed with each other or that are “less successful” breeding within their population then outside of it. They don’t exist. Just ask anyone descended from Thomas Jefferson.



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  • 81
    Red Dog says:

    In reply to #77 by Galaxian:

    It’s news to me that subspecies (race) is a vacuous term for a biologist.

    Meaningless was probably the wrong word to use. What I should have said is not very interesting from a biological standpoint. What I meant is that what human society considers “racial” characteristics are a very small number of traits in the genome and that there is no evidence that people who share those traits have any significant within group similarities worth mentioning. As biologist Jerry Coyne said:

    “How different are the races genetically? Not very different. As has been known for a while, DNA and other genetic analyses have shown that most of the variation in the human species occurs within a given human ethnic group, and only a small fraction between different races. That means that on average, there is more genetic difference between individuals within a race than there is between races themselves.”

    Source: Are there human races?



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  • 82
    Galaxian says:

    In reply to #78 by Red Dog:

    In reply to #75 by Red Dog:
    

    “You ignored my questions. In your previous comment you said:

    there definitely are human populations who, a) Avoid interbreeding, and, b) Whose cross-fertility is higher or lower depending which population they might decide to breed with.
    

    I say that is bullshit and challenge you to come up with some examples of human populations that can’t interbreed with each other or that are “less successful” breeding within their population then outside of it. They don’t exist. Just ask anyone descended from Thomas Jefferson.”

    Well, that’s easy. Start with Rhesus Factor and carry on from there… You might also consider the implications of the Danish cousins survey:

    http://www.sciencemag.org/content/322/5908/1634.2.full

    that indicates that maximum fertility is reached at the 3rd cousin level.

    BTW; Neanderthals were a SUB-species of Homo sapiens: they could interbreed with Cromagnon. Recent research shows up to about 8% influence in Caucasian populations.

    And yes, I’ve already pointed out that according to current systematics, societal prejudice can be used as a basis for species differentiation, here in post #76 : **
    “The traditional rule has indeed been flawed in that cultural preferences have come into it; such as the avoidance of some birds to plumage of a different color, or some fish to different markings, even though they are quite cross-fertile. thus their prejudices are taken into account. Well, on that account Jews & Muslims should be categorized as different species (they are reluctant to interbreed), eh?” ;-)**



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  • 83
    Galaxian says:

    In reply to #79 by Red Dog:

    In reply to #77 by Galaxian:

    It’s news to me that subspecies (race) is a vacuous term for a biologist.

    Meaningless was probably the wrong word to use. What I should have said is not very interesting from a biological standpoint. What I meant is that what human society considers “racial” characteri…

    Well, what’s * not interesting* to one biologist is very interesting to another, so let’s leave that aside.

    Infact, earlier in the same article, Coyne said that there ARE races. And his POV that you rest on is called Lewontin’s Fallacy, and has been fully debunked over the past decade, including by Richard Dawkins’ in “The Ancestor’s Tale”.

    I really don’t see what the problem is. Human subspecies/race is only of concern if you prefer a world of bland uniformity, so you have to either exterminate variety or pretend that you’ve exterminated it.

    As for myself, I’m uplifted whenever I see someone of H.erectus or H.denisovan admixture (as I often do. BTW, I have a great deal of Neanderthal in me, including the morphological features… doesn’t bother me one way or another).



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  • Human populations are never quite isolated, they are always inher acting, intermixing, intermarrying and interacting sexually with neighboring populations and while there may appear to be a great difference between people from populations native to opposite or very distant regions of the world the genetic differences between neighboring populations are slight and the variations are gradual from one neighboring population to the next, from one end of the world to the other between which the differences may appear great. So humans are essentially one continuous population.


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  • Without typos.

    Human populations are never quite isolated, they are always interacting, intermixing, intermarrying and interacting sexually with neighboring populations and while there may appear to be a great difference between people from populations native to opposite or very distant regions of the world the genetic differences between neighboring populations are slight and the variations are gradual from one neighboring population to the next, if they may appear great between populations from distant regions or from one end of the world to the other. So humans are essentially one continuous population.


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  • We may yet speciate into Eloi and Morlocks. The separation of gated communities, fenced off nations may yet lay a path to Elysium. We may yet get to eat the rich. (I tend to think Morlock. Possibly the first Morlock was Henry Straker in Man and Superman.)

    Until then I think we might usefully think of ourselves as four or five cognitively discernible subspecies, divided by those genetic drivers for differing modes of neural pruning. The aspie, the schizotypal, the anxious/OCD, and alpha/psychopath, offer cultures a broad and useful tool set of abilities that are enabled by a burgeoning morality. Notably, though much interbreeding happens, especially at the behavioural edges, these groups tend to select their own as partners, maintaining a sufficient distinction to be useful. I think “cognitive sub-species” might be a phenomenon in the higher primates and other sophisticated socialising animals.


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  • This point may have been address above, if so, I apologize, but is it possible that we haven’t seen any major evolutionary changes within our species because we are so young?  I understand that homo sapiens have been on the planet for a few tens to hundreds of thousands of years, but even if it were a million or more, isn’t that a blink of an eye in geological time.  We should come back to this discussion after humans have been here for a couple billion years.  One other thought, maybe we are the first species to be able to engineer our own evolution via artificial intelligence, a process that has only recently begun.


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  • Hello Everyone!

    I love that many old buddies are still posting.  I have not read the entire thread, so i do not know if this has been breached. I’d like to steer this speciation discussion to a galaxy far far away……

    I hypothesize that colonization of Mars (or another planet or satellite) would generate allopatric speciation whose primary driving force would be differences in gravitation between earth and the other planet (or moon).  There would be genetic isolation, two different sets of conditions, and time.

    I propose that anatomical and physiological changes to humans would accumulate very very quickly (changes in eye shape are demonstrated after brief trips into space).  So quickly that I’d expect to see speciation in a low number of generations.

    Thoughts?


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  • Nice to see you back.

    crookedshoes/

    I hypothesize that colonization of Mars (or another planet or satellite) would generate allopatric speciation whose primary driving force would be differences in gravitation between earth and the other planet (or moon).  There would be genetic isolation, two different sets of conditions, and time.

     

    The low gravity on the Moon and Mars do pose some interesting questions.  Especially in the light of the detrimental effects on human health, which have been identified on the ISS.

    I do in fact have quite a lot of ideas about possibilities on Mars.

    https://www.quora.com/If-Marss-atmosphere-is-95-97-CO2-would-transporting-plants-to-Mars-in-an-attempt-to-plant-them-there-possibly-be-a-way-of-taming-Marss-atmosphere/answer/Alan-Appleby-4

     

     



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  • I’ve been very very busy, working on a really cool project involving evolution education in high school classroom.  It was funded through an NSF grant and has run for three years.  We go live in June 2020.  It is cutting edge stuff — I cannot wait to be able to drop the website name and info (but am not able to, yet).  Anyway, I always read the threads, but rarely am in a position to comment.

    I missed all of you as well.  Nice to be back (even if it’s only for a brief window)

     


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