Darwin Day 2015 Questions #5- Is every offspring a ‘slightly new’ species?

Mar 31, 2015

Richard Dawkins answers your questions about evolution in honor of Darwin Day 2015.

“Is every offspring a ‘slightly new’ species? how does this work?”

Edited by Stephanie Renee Guttormson

Copyright 2015 Richard Dawkins Foundation for Reason & Science

40 comments on “Darwin Day 2015 Questions #5- Is every offspring a ‘slightly new’ species?

  • I understand that closely related species often have a different number of chromosomes or different lengths of chromosomes. This difference would stop egg and sperm from merging, right? The mutation that causes this a massive one. Let us say we have one individual who has made the jump. Who does he breed with? Let’s say by some highly improbability there is another. Then that pair are in the same boat an endangered species down to 2 individuals. They have no genetic diversity. They should be toast, right? Add one more improbability, why would these two find each other more attractive than non-flipped individuals?



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  • Roedy Mar 31, 2015 at 11:26 pm

    I understand that closely related species often have a different number of chromosomes or different lengths of chromosomes. This difference would stop egg and sperm from merging, right? The mutation that causes this a massive one. Let us say we have one individual who has made the jump. Who does he breed with?

    There is considerable research on this studying trout. Mortality rates and infertility rates are high but not 100%.

    http://link.springer.com/article/10.1007%2FBF00266992
    First generation tetraploids were produced by hydrostatic pressure treatment before the first cleavage and raised until the adult stage. Their survival and growth were severely depressed when compared to the diploid control: after two years, no ovulated females were found although males produced sperm at 1 and 2 years of age and were mated individually with diploid females. The progenies were consistently normal with high survival rates. They were found to be almost all triploids by karyology, which failed to detect a significant rate of aneuploidies. However, the fertilizing ability of tetraploid males was always low (0 to 97% of the control; average 40%).

    http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2109.1993.tb00640.x/abstract
    Initiation of tetraploid breeding line development in rainbow trout, Oncorhynchus mykiss (Walbaum)

    Survival rates of tetraploids were low and loss frequencies did not stabilize till the age of 9 months. Thirty-three tetraploid fish, individually checked by measurements of DNA content, nuclear cell size and number of nucleoli per cell, were found at the age of 17 months. Body weights of survivors were similar for tetraploids and diploids throughout the whole testing procedure.



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  • As I understand it, any mutation that would lead to speciation cannot be so radical that it would result in the inability to leave offspring. (Makes sense, right?)

    The mechanisms don’t apply to individuals – they work on populations.



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  • Roedy
    Mar 31, 2015 at 11:26 pm

    I understand that closely related species often have a different number of chromosomes or different lengths of chromosomes. This difference would stop egg and sperm from merging, right? The mutation that causes this a massive one. Let us say we have one individual who has made the jump. Who does he breed with?

    First, Why would this stop egg and sperm from merging? Perhaps the sperm could enter but the problem would be the mismatch of different number of chromosomes or different lengths?

    Roedy’s comment shows the difficulty of reconciling the huge expanse of time that we are dealing with here, several hundred thousand years, of divergence in the case of humans/Neanderthals, and millions of years in the case of humans/chimps and the seemingly abrupt “massive” mutations like a fusion of two chromosomes that exists between humans and the other apes.

    Here is a paragraph from Wiki explaining the situation:

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

    Human and chimpanzee chromosomes are very similar. The primary difference is that humans have one fewer pair of chromosomes than do other great apes. Humans have 23 pairs of chromosomes and other great apes have 24 pairs of chromosomes. In the human evolutionary lineage, two ancestral ape chromosomes fused at their telomeres, producing human chromosome 2.[3] There are nine other major chromosomal differences between chimpanzees and humans: chromosome segment inversions on human chromosomes 1, 4, 5, 9, 12, 15, 16, 17, and 18. After the completion of the Human genome project, a common chimpanzee genome project was initiated. In December 2003, a preliminary analysis of 7600 genes shared between the two genomes confirmed that certain genes such as the forkhead-box P2 transcription factor, which is involved in speech development, are different in the human lineage. Several genes involved in hearing were also found to have changed during human evolution, suggesting selection involving human language-related behavior. Differences between individual humans and common chimpanzees are estimated to be about 10 times the typical difference between pairs of humans.[4]

    It just seems highly improbable, on the face of it, to think that this type of mutation, two fused chromosomes, could happen in any way that is gradual enough to allow viable offspring. Was it gradual? Or maybe I’m making a big deal out of something that is more common than I think. Do chromosomes fuse and break more easily than I imagine they do? It really does seem that if this is a situation where an individual presents with this mutation, then his prospects of reproduction are doomed and then there goes the fused chromosome with him. But this can’t be the case because the evidence is all around us that the fused chromosome mutation was not the deal breaker that I think it is!

    I’m having a hard time with this. 🙂



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  • I was born without any wisdom teeth in my head at all; none to grow in at a certain age. I was told by a physician, this was evolution. So, I had babies with a man who had all his wisdom teeth, but my kids, all grown with their own kids now, only had 2 wisdom teeth each.

    If I had found a man who also had no wisdom teeth, would our kids have had no wisdom teeth?

    This is how I’ve always thought about evolution. It is happening all the time, just so slowly, it’s not noticble between generations.



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  • Defining a species is more complicated than if they can interbreed though, isn’t it? I’m thinking of Homosapien vs Neanderthal. Homosapien partially bred them out yet they weren’t the same species, were they? Or am I just misunderstanding that and they’re technically the same species?



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  • Cliff Apr 1, 2015 at 1:00 pm

    Defining a species is more complicated than if they can interbreed though, isn’t it? I’m thinking of Homosapien vs Neanderthal. Homosapien partially bred them out yet they weren’t the same species, were they? Or am I just misunderstanding that and they’re technically the same species?

    They were closely related “species” or maybe “sub-species”.
    Evolving species don’t necessarily fit into convenient human classification boxes.

    Humans look a bit isolated because the more closely related species of Homo have gone extinct.

    If we look at the family of dogs ( ie. Canids), there are lots of hybrids and back-crosses between species. http://en.wikipedia.org/wiki/Canid_hybrid

    Often species boundaries are blurred, based on geographical isolation, or simply complex, – as with ring species. http://en.wikipedia.org/wiki/Larus#Ring_species



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  • Different species can readily breed though. I’m most familiar with reptiles so I will use a few examples of snakes. Many species in the family Colubridae are capable of interbreeding. In N. America this includes clearly different snakes such as milksnakes, kingsnakes, rat snakes, gophersnakes/bullsnakes/pinesnakes, foxsnakes, and racers. I’ve seen wild caught cottonmouth-copperhead hybrids in the Vipera family as well.

    Is the taxonomy just horribly misused at categorizing these animals? Are reptiles exceptions? I’m more inclined to believe the former as taxonomy is not a perfect art.



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  • Cliff Apr 1, 2015 at 1:00 pm

    Defining a species is more complicated than if they can interbreed though, isn’t it?

    While the definition of two separate but related species, is based on their inability to produce fertile offspring, (as with the mule), the slow moving apart of the branches on the tree of life, usually leads to progressive levels of infertility, rather than a sudden cut off.
    This can be easily seen in plants where the occasional fertile hybrid, is found among its more numerous sterile siblings.



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  • Dale Apr 1, 2015 at 1:27 pm

    Is the taxonomy just horribly misused at categorizing these animals? Are reptiles exceptions? I’m more inclined to believe the former as taxonomy is not a perfect art.

    I’m no specialist on snakes, but taxonomy generally is being revised as DNA analysis, replaces the earlier observation based systems, based on similarities in phenotypic structures.



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  • It’s interesting sometime I think the genetics of a species “tread water” waiting for a stimulus to drive change a physical/mental or social imperative.

    I actually breed dogs in a very controlled line breeding program, the ethos of this program has to make selections on health, function and tested physical ability. This is vastly different to how other breeders approach breeding pedigree animals and it shows.

    Some of the pedigrees we use are now more then 12 generation on from the last foreign genetic material was added. While these animals are of coarse canine they are different animals from the animals from which they are derived from, they are there own sub species or breed.



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  • Speciation is not an ontological division in nature, nor in fact any real division in nature. It is a taxonomical division decided by a confabulation of scientists. It is a scientific naming convention not a fact of nature. So to get answer to the question, is every offspring a new species, you would need to assemble all the reputed animal taxonomists in the world, and then ask them to vote on the matter.



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  • I submitted a question to Dr. Dawkins basically, step by step, what happens when a new species forms. He gave a broad overview, but I would like an explanation that talked about what happens at various generations at a chromosomal level. This question is both puzzling for people trying to understand speciation and for debating
    Christians who claim it cannot happen. The one answer given here is change in chromosome number and lengths need not be accomplished in a single generation.



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  • 18
    Elijah says:

    Is a loss of the ability to interbreed really the criterion for the formation of a new species? Tigers and lions, horses and donkeys, etc. are of different species but can interbreed (although in most if not all cases the hybrid offspring are infertile).



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  • (although in most if not all cases the hybrid offspring are infertile).

    And that is the definition of species. The cross breads can no longer pass on their genes. The ability to produce offspring is just a shadow on there once common ancestor living on in their collective genomes.



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  • Elijah Apr 2, 2015 at 2:50 am

    Is a loss of the ability to interbreed really the criterion for the formation of a new species? Tigers and lions, horses and donkeys, etc. are of different species but can interbreed (although in most if not all cases the hybrid offspring are infertile

    In species / sub-species of domestic and wild dogs, there are various types of fertile hybrid.

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

    This article is lacking citations for some claims, but many of the claims check out elsewhere.



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  • It is clear that it is difficult to define a species. Mayr’s definition is a convenient one, however my thesis was on the salamander Ensatina (See ensatina.net). It is a ring species in the process of speciation as there is ample evidence of incipient species formation between some of the populations. Two populations of Ensatina (eschscholtzii and klauberi) are different species by every definition. However these two populations are connected by a ring of populations and it is difficult to draw a line where one species begins and the other ends.



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  • David R Allen Apr 2, 2015 at 3:29 am

    (although in most if not all cases the hybrid offspring are infertile).

    And that is the definition of species. The cross breeds can no longer pass on their genes. The ability to produce offspring is just a shadow on their once common ancestor living on in their collective genomes.

    There are one or two interesting examples of closely related species in flowering plants, in the same habitat, where they could cross-breed but generally don’t, because one species is day flowering, and the other has evolved to be night flowering with different pollinators.



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  • In California, there is are plethodontid salamanders of the ring species Ensatina eschscholtzii that form a ring of seven subspecies, two of which meet in Southern California. Those two subspecies are an unbloched form eschscholtzii and a blotched form klauberi. They are very different in coloration and occupy somewhat different forested habitats. In the Cuyamaca Mountains the two subspecies meet and there is no evidence of interbreeding and no hybrids between them. Just 35 miles north near Palomar Mountain, the blotched and unblotched subspecies meet but produce only about 3% hybrids. Tom Devitt found that blotched females would mate with unblotched males, however unblotched females would not mate with blotched males.

    In the Cuyamaca area, the two “subspecies” are different species by every definition (Dave Wake, UC Berkeley). Yet what would you call the two “subspecies” in the Palomar Mountain area? In addition, the “subspecies” eschscholtzii and klauberi are connected statewide by a ring of “subspecies.” It does not appear that there is any clear cut definition for the term species, a convenient one by Mayr perhaps, but not universal in its application.



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  • 24
    aroundtown says:

    I wonder if modern humans could have theoretically breed with hominids of the past? When we diverged into Homo Sapiens did we transgress past our ancestors? Would we have become incompatible as breeding partners or is it something like Neanderthal’s and subsequent interbreeding that remained compatible? Can it run forwards or backwards in time is what I wonder? Regressive breeding compatibility. Just curious and please excuse my ignorance on what is probably information that should be readily understood. I am thinking about parallels in the recent discussion on Mammoths and the connection with modern day elephants as a possible bridge in bringing them back as well.



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  • Someone (Alan?) may be able to find the reference: I read someplace of a set of bird populations, species perhaps, that live all around the earth. Each population can interbreed with the adjacent one to east and west. Except in once place, where the adjacent populations can no longer interbreed.

    Excuse mangled terminology here, I’m trying not to get it wrong, but the point was, it was an example where A can breed with B which can breed with C …. but Z can’t breed with A. So Z and A are different species, one would suppose. But are Y and Z different species?

    Forgetting which kind of birds they were (terns? gulls?) I can’t manage to locate the original reference. I’m sure that I didn’t just imagine it though. It makes the “whats a species” question a whole lot more tricky.



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  • OHooligan Apr 4, 2015 at 4:02 am

    Someone (Alan?) may be able to find the reference: I read someplace of a set of bird populations, species perhaps, that live all around the earth. Each population can interbreed with the adjacent one to east and west. Except in once place, where the adjacent populations can no longer interbreed.

    There is a link on this thread:-

    https://www.richarddawkins.net/2015/03/professor-richard-dawkins-biology-changing-the-world-interview/#li-comment-173910



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  • Variations in the number of chromosomes in humans is not as uncommon as you might think. People with some level of Down Syndrome (1/1000), for example, have an extra copy of part or all of chromosome 21. Fertility in females with the full or near full condition is not high but far from zero. Fertility in males with the same condition is far lower, probably because they are prevented from being sexually active, but still not zero. The probability their offspring will have the condition varies, with the extent of their condition which relates to how much of an extra copy of chromosome 21 they have and what part is copied.

    Down Syndrome is only one of many genetic disorders involving different numbers of chromosomes and, in most cases, people with these other conditions can also produce offspring.

    Eventually, with enough natural selection, it is possible, some sort of stable variation with more or less chromosomes will arise from one of these mutations.



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  • Speciation in plants can’t be accurately compared to speciation in animals. Clines are extremely common in the plant kingdom but much rarer in the animal kingdom mainly because of a lack of mobility with plants. “Ring Species” or completely folded clines where the geographical area is linear rather than circular, are also quite common with plants, that is, where both ends of the cline are in the same geographical location.

    Thus there is a lot more of a grey area between one species and another with plants than there is with animals.



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  • We will never know if modern humans could interbreed with ancestral forms. However, think of the controversy that would be raised if a chimpanzee were artificially inseminated with human sperm and that procedure produced a living hybrid!



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  • cbrown Apr 4, 2015 at 4:51 pm

    We will never know if modern humans could interbreed with ancestral forms.

    I think the geneticists have found some Neanderthal DNA and Denisovian DNA in human genomes.

    http://phenomena.nationalgeographic.com/2014/07/02/sex-with-extinct-humans-passed-high-altitude-gene-to-tibetans/

    In 2010, Rasmus Nielsen from the University of California, Berkeley found that Tibetan people have a mutation in a gene called EPAS1, which helps them handle low levels of oxygen. Thanks to this mutation, they can cope with air that has 40 percent less oxygen than what most of us inhale, and they can live on a 4,000-metre-high plateau where most of us would fare poorly. To date, this is still “strongest instance of natural selection documented in a human population”—the EPAS1 mutation is found in 87 percent of Tibetans and just 9 percent of Han Chinese, even though the two groups have been separated for less than 3,000 years.

    But when the team sequenced EPAS1 in 40 more Tibetans and 40 Han Chinese, they noticed that the Tibetan version is incredibly different to those in other people. It was so different that it couldn’t have gradually arisen in the Tibetan lineage. Instead, it looked like it was inherited from a different group of people.

    By searching other complete genomes, the team finally found the source: the Denisovans! The Tibetan EPAS1 is almost identical to the Denisovan version. It’s now a Tibetan speciality, but it was a Denisovan innovation.

    Denisovan DNA makes up 5 to 7 percent of the genomes of people from the Pacific islands of Melanesia. Much tinier proportions live on in East Asians. And now, we know that some very useful Denisovan DNA lives on in Tibetans.

    Svante Paabo, who sequenced the Denisovan genome, is delighted. “It’s very satisfying to see that gene flow from Denisovans, an extinct group of archaic humans which we discovered only four years ago, is now found to have had important consequences for people living today,” he says.



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  • Can somebody educate me, please?

    Doubt 1.
    How many homo do exist NOW? Yes, the standard model says there is one: Homo Sapiens Sapiens. Fine for me.

    However, the non-interbreeding is happening in several forms:

    :: People who starve (and/or are sick) do they interbreed with aristocratic/monarchy/oligarchy people? Of course not except in raping cases or similar…

    :: What it seems to me it is that people interbreed with “equals” so this “equalization” makes a specie in the long run or not?

    Doubt 2.

    When the merging between Homo Sapiens Sapiens and AI (Artificial Intelligence) happens what will happen in terms of new specie?



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  • Physical anthropology is not my specialty. However the evidence seem to support the hypothesis that Neanderthals infrequently interbred with Homo sapiens. Perhaps H. sapiens used tools and weapons more effectively than Neanderthals and as a result could raid villages and take young women forcibly, mating with them producing “hybrids.” It is still not known if the Neanderthals were a separate species from Homo sapiens, but were so closely related genetically that offspring produced from crosses between the two species (or subspecies?) could survive and would produce fertile backcrosses. The same could be said about the Denisovans and Homo sapiens. Whatever the case may be, a clear definition of the taxonomic category of “species” is difficult to define.



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  • WhoAreWe Apr 5, 2015 at 11:03 am

    How many homo do exist NOW?

    It is arguable that the genus Pan (Chimps and Bonobos) could also be considered species of Homo.

    Yes, the standard model says there is one: Homo Sapiens Sapiens. Fine for me.

    All modern humans are the same species: – Homo sapiens.



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  • 34
    aroundtown says:

    At this point both posts bring up greater questions for me which will require some homework I’m thinking. Interesting to note the revulsion at a possible sideways path from our current prominence specied form. Secondly the information on Denisovans raises a huge question for me, if the specialized genetic trait for higher functioning at altitude was passed onto the homo sapiens species it clearly was not distributed among the entire population of homo sapiens, very interesting indeed.

    Homo sapiens are known to have a small percentage on Neanderthal dna but once again it is not a complete distribution just like the Denisovans genetic contribution. What peaks my interest is the suggested waves out of Africa (two have been proposed) would still have been extremely small gene pools initially yet the distribution of genetic mutation and cross propagation would possibly suggest small pockets of isolated groups that never encountered each other long enough to make the imprint disseminated among the entire populace within their respective groups. Seems like a difficult thing to accomplish with our early hunter gatherer distinction. Seems like we would have crossed paths more often.

    Could it have been something like the American indians who shunned nearby groups and were hostile to each other or something else at play that prevented cross breeding?



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  • Steve Apr 1, 2015 at 3:18 pm

    Speciation is not an ontological division in nature, nor in fact any real division in nature.

    It may or may not be, depending on the existence or extinction of intermediates.

    It is a taxonomical division decided by a confabulation of scientists. It is a scientific naming convention not a fact of nature. So to get answer to the question, is every offspring a new species, you would need to assemble all the reputed animal taxonomists in the world, and then ask them to vote on the matter.

    . . . . Or we could just look up the code at the
    International Commission on Zoological Nomenclature http://iczn.org/
    The International Commission on Zoological Nomenclature (ICZN) acts as adviser and arbiter for the zoological community by generating and disseminating information on the correct use of the scientific names of animals. The ICZN is responsible for producing the International Code of Zoological Nomenclature – a set of rules for the naming of animals and the resolution of nomenclatural problems.



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  • All humans are of one single species; Homo sapiens. The various “races” of the world are all within this species. Various people in different class groups are again in just one species. Any lack of interbreeding among these various groups is strictly a result cultural divisions and has nothing to do with any slight genetic differences that may exist.

    By the way, the term “specie” is not singular for the biological taxonomic term “species.” “Specie” is singular for money in the form of coins.



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  • If all breeds of dogs were eliminated except Great Danes and Chihuahuas, then there would be two different species. Physical differences can and do act as reproductive isolating barriers. Even if they could be artificially inseminated and the hybrids survive and could interbreed, does not mean they are the same species.



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