Number of chromosomes and evolution

Jul 8, 2013

Discussion by: typingcat

I happened to read an article on a Christian news web site. It was about some Korean professors gathering together to discuss gay problems. One professor objected the government's decision to illegalize discriminations to gays. His logic is, if the government “forces” people not to discriminate gays, it will “force” people to think that gays are “normal”.

I am not gay, but that made me angry, so I searched Google for his name. It turned out that he was a Christian, but also a biology professor in a fairly well-known university. His bio is at According to the site, he got a doctorate in the University of Oxford, department of zoology. Maybe he actually met Dr. Dawkins.

Google also gave me one of his articles. ( ) In that article, he criticized Dr. Richard Dawkins and those who say human are evolved from primitive animals. Well, if it was a stupid Christian like Ray Comfort, I would have no problem to dismiss his argument, but this is a biology doctor from Oxford University. He should know everything I know about biology and a whole lot more. How come a person like his knowledge can deny evolution? I thought only suckers deny human evolution.

Most of his criticism was like the usual one I can find Christian web sites, so I could easily dismiss them, but one thing I did not know how to respond was the following paragraph.

“Evolutionists believe that species evolve by showing the following as an example: when a polyploidy is formed in a plant by mutation,  it cannot make offspring with the original species, and thus diverges into a new species. Mutated individuals that have an even chromosome set (e.g., 4n, 6n) meet the original forms who have 2n, 3n respectively and can be fertile. However, if a mutated plant has 3n, it cannot find a mate and thus cannot make offspring. Many seedless fruits are produced by such 3n plants. They are always sterile because they lack seeds, but we can reproduce them by grafting. However, in higher animals polyploidy is lethal or the extra chromosome makes the animals sterile. This may not seem to be a big problem because this matter belongs to scientific field. The problem is that whether human can be evolved from a protozoic cell by many steps.”

(I translated it from Korean, so there may be some grammatical errors and wrong terminology.)

His last -1 sentence, “This may not seem to be a big problem” is there (I do not know why), but the fact that it was the only scientific argument against evolution in his article, he must be thinking this is a big problem. I heard that humans have one less chromosome when compared to chimpanzees, because two chromosomes were merged. If that was a mutation, how the first individual when one less chromosome could be fertile? Does the number of chromosomes and fertileness make any difficulties in the evolution theory? Is the professor making a valid argument agains evolution, or is he just making a wordplay with an already-dismissed argument?



14 comments on “Number of chromosomes and evolution

  • 1
    SaganTheCat says:

    What’s the name of this professor? I suspect some fraud somewhere…

    However, in higher animals polyploidy is lethal or the extra chromosome makes the animals sterile. This may not seem to be a big problem because this matter belongs to scientific field. The problem is that whether human can be evolved from a protozoic cell by many steps.” not sure how many logical falacies are commited here but certainly begging the question and a red herring,

    using the example of grafting plants (organism whos ancestors split with ours well over a billion years ago) simply states humans and plants are very different. trying to bridge an evolutionary gap between the two seems impossible, and it is, but it’s a misdirection to suggest the gap must be bridged. Humans did not evolve from plants any more than plants evolved from humans and the use of “higher animals” creates the illusion of a hierachy which does not exist in nature.

    I can’t answer the chromosome number question but home someone does as I’ve often wondered the same but it’s never been a problem to accept as chromosome numbers vary throughout nature yet there is a single ancestor. at some point species split, and over time chromosome numbers can change i guess. maybe the idea that the fused chromosome was the cause of the split.

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  • Chromosome counts are poor indications of similarity; they can vary widely within a single genus or even a single species. The plant genus Clarkia, for example, has species with chromosome counts of n = 5, 6, 7, 8, 9, 12, 14, 17, 18, and 26 (Lewis 1993). Chromosome counts in the house mouse species (Mus domesticus) range from 2n = 22 to 40 (Nachman et al. 1994).

    Chromosomes can split or join with little effect on the genes themselves. One human chromosome, for example, is very similar to two chimpanzee chromosomes laid end to end; it likely formed from the joining of two chromosomes (Yunis and Prakash 1982). Because the genes can still align, a change in chromosome number does not prevent reproduction. Chromosome counts can also change through polyploidy, where the entire genome is duplicated. Polyploidy, in fact, is a common mechanism of speciation in plants.

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  • 3
    Jos Gibbons says:

    Chromosome fusion doesn’t matter at all because chromosomes line up with one another based on the detection of similar or identical genes, so if a gamete in which chromsomes m, n are fused unites with one in which they aren’t m and n pair up next to mn, and the resulting individual is fertile.

    Polyploidy produces fertile$ plants if and only if the number of sets of chromosomes is even, which is guaranteed if the first cell division accidentally fails, which is the cause of almost all polyploidy in nature. Cases such as 3n bananas are much rarer because they require a meiosis to accidentally give all the chromosomes to a gamete.

    $ Unless humans cloning it counts as fertile, which isn’t true in evolutionary terms, but that’s the only reason we have seedless commercial bananas. They probably date to a single 3n mutant found in South East Asia in the 14th century (according to a former biology teacher of mine). Luckily, cloning by artificial vegetative propagation has been known for many centuries.

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  • 4
    MitorTheBold says:

    Without getting into the ins and outs of biology (mainly because I don’t have the requisite knowledge) this is simply another pontification on the minutiae of the scientifically arcane while glossing over the alternative to evolution which is that god made us in one fell swoop out of dust. Now, forgive me if I’m missing something here but is there something of an evidence gap between these two explanations for life on Earth? Sure, there may be some details in the theory of evolution that might require some further explanation or even research – but there is a mountain of evidence both in the fossil record and in observable phenomena around us to corroborate evolution by natural selection while there is absolutely zero for making life out of dust.

    If the only thing missing from Creationism were some minor details regarding the particular molecules of dust which otherwise had been observed to spontaneously generate fully-formed life on the say-so of an all-powerful supernatural being then maybe I’d be persuaded to look into it. However, what is missing from Creationism is any evidence whatsoever.

    Doing biology at Oxford is not an infallible method of avoiding nonsense; and besides, look at the majority of Oxford Biology graduates to see what knowledge of this subject does for faith – there will always be noisy and deluded exceptions.

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  • 5
    Red Dog says:

    A while ago I had a debate with some people about whether or not ex-Catholics should go through the formal exit rituals of the Catholic church. One of the points I made is that its kind of futile to play the game of people who are illiterate and who obviously have no regard for truth or evidence. To start basing your decisions on things like “the nut jobs say X so that means i must think or do not X” seems to me to be going down a pointless rat hole. And this article is a classic example of what I mean. Why anyone would waste so much time refuting a guy who obviously doesn’t know what he’s talking about is beyond me. Studying actual biology by credible biologists seems so much more interesting and productive.

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  • 6
    crookedshoes says:

    I am curious as to what this good professor’s name is? I clicked on the link to his paper, but it is in Korean (I guess) and looks very daunting to me!

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  • 7
    Callinectes says:

    When the chromosome difference is just because two have merged or one has split, that does not result in infertility problems. 2 Chromosomes can “pair” with one when the genes are the same. It might not quite as good as a straight-up match, but it still works. But even this slight difference in fertility will contribute to speciation, as proper matches have a better chance of success.

    So this chromosome change does not make the individual chemically infertile with its fellows, but it does make it more chemically fertile with those that share this abnormality, and after a few generations there will be such individuals available to breed with. Or maybe the difference in fertility only occurs with chromosomal inversions, I’m not quite sure.

    PZ Myers posted a similar topic to his blog a few weeks ago

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  • 8
    steve_hopker says:

    In reply to #1 by SaganTheCat:

    What’s the name of this professor? I suspect some fraud somewhere…

    I agree. I’ve not got graduate level genetics (and I can’t read a word of Korean!) but the argument as reported about mutations seems to ignore the fundamental that chromosomes (excepting the sex chromosomes) are paired (thuogh the text as given is not easy to follow). Even worse, the text as given suggests that mutation changes the number of chromosomes not – as surely many lay people know, the DNA within chromosomes. Unless Oxbridge have had a calamitous decline in their standards, ie to below GGCSE ‘O’level’, surely even the most miserably incompetent and party animal Oxford Biology undergraduate would recognise this as total rubbish, let alone someone supposed to be at professorial level.

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  • 9
    Alan4discussion says:

    These links will be helpful for those needing examples of polyploid species or background information.

    Parade of Polyploids


    Given that polyploidy is a fundamental process in biology, it is important to extend information from our project to a more general audience, especially educators. To achieve this goal, we have prepared manuscripts for educators that present concepts on polyploidy and their significance in biology.

    Chromosome numbers vary widely, from 1260 in the Adders tongue fern, to one for the haploid male Jack jumper ant.

    List of organisms by chromosome count – From Wikipedia, the free encyclopedia

    Polyploid offspring, are of course the exception, rather than the norm.

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  • 10
    Alan4discussion says:

    @OP However, if a mutated plant has 3n, it cannot find a mate and thus cannot make offspring. Many seedless fruits are produced by such 3n plants. They are always sterile because they lack seeds, but we can reproduce them by grafting.

    Triploid hybrids are sterile because odd numbers like 3 chromsomes cannot form pairs -unless they (rarely) double up to become hexaploid with six chromosomes.

    However, in higher animals polyploidy is lethal or the extra chromosome makes the animals sterile.

    This is usually so, but not always. There are exceptions. They are usually sterile or disabled, but here is an example of fish, where there are sterile triploid hybrids and fertile tetraploid individuals.


    Heat shocks were applied to rainbow trout eggs, starting between 5h and 9h after fertili-zation. The frequency of occurrence of tetraploid was 5% in fish of twelve-month-old.

    Triploid trout are deliberately bred to prevent the introduced stocking of Rainbow trout cross breeding with native species.

    Fish and Game fisheries biologists have learned that non-native rainbow trout have the ability to breed with native cutthroat trout and thus produce hybrids or aquatic “mutts;” fish that are neither full rainbow nor full cutthroat trout. Should hybridization occur often enough over a long period of time, Idaho’s three cutthroat species might be lost forever.

    To remedy this problem, Fish and Game simply quit stocking rainbows at locations with self-sustaining cutthroat populations and instead shifted those rainbows to other waters. However, rainbow trout do not always stay where you put them. It seems rainbows like their freedom and often choose to swim long distances, upstream or downstream, to find spawning areas and mates. This problem took biologists back to the drawing board. How do you stop highly mobile hatchery rainbows from spawning with wild, native cutthroat?

    It turns out there is a way, but the process is a complex one. When trout spawn, the female’s eggs possess two sets of chromosomes and the male’s sperm possess one set. After the eggs are fertilized, the chromosomes recombine and each egg inherits one set of chromosomes from the female and another set from the male — similar to humans. The third set is then kicked out of the egg. Rarely in the wild, an egg will “forget” to kick out the third set and the fish becomes what is known as a triploid (possessing three sets of chromosomes). Triploid fish look, swim, jump, and taste like normal fish, except for one important difference—they never develop normal eggs or sperm and are unable to reproduce (i.e., they are sterile).

    Through experimentation with this natural process, researchers found that they could create triploid trout both by exposing trout eggs to pressure and by placing trout eggs in a warm water bath shortly after fertilization. Both processes inhibit a trout egg’s ability to kick out that third set of chromosomes and voila, a triploid fish is born.

    After several detailed experiments, Fish and Game biologists adapted these techniques for use in the state’s rainbow trout egg collection facility at Hayspur Fish Hatchery. And since 2001, approximately nine to 10 million rainbow trout eggs have been sterilized in this manner each year. Raised to catchable size, these fish are now being stocked in waters across the state.

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  • “Normal” has multiple meanings. It means common. You could say “A cold in winter is normal for human sapiens” This does not imply people with out one should treated to have one.

    You might say “right handedness is normal in homo sapiens” but it not mean society must work to eliminate the left handed.

    It can mean “not pathological”. If your infant has pointed ears, don’t worry, that is normal and causes no problems.”

    In common speech it means “not disgusting”. Eating cow is normal where eating dog is not. Putting your tongue in another’s mouth is normal but licking their eyeballs is not. What is disgusting primarily depends on what one in familiar with from childhood.

    Christians like to say similar phrase, “being gay is not natural” even though it clearly in quite common in nature, dozens of species. What they really mean is contemplating it makes them feel uncomfortable ,

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  • The number of chromosomes do not really matter. Evolution is not about the number of chromosomes. To keep it in a bit simple terms: chromosomes are only “boxes” with genetic information.You can take the information from 2 boxes and merge it into 1 bigger box or do the opposite. The information remains te same. As long the molecules that help with/regulate gene transcription, DNA-replication (and much more prosesses) are still able to do their job with the rearranged information there should be no problem.

    That is pretty much the awnser I give to my students (age: 14-15) when they ask me that question. It remains an interesting and challenging question though 🙂

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  • In reply to #12 by FrankH:

    The number of chromosomes do not really matter. Evolution is not about the number of chromosomes. To keep it in a bit simple terms: chromosomes are only “boxes” with genetic information.You can take the information from 2 boxes and merge it into 1 bigger box or do the opposite. The information remai…

    It depends I would say. I assume you don’t want them to draw conclusions about evolution from chromosome numbers of different species? “Boxes” losing/changing integrity is not trivial. E.g. an individual carrying a balanced translocation usually has reduced fertility because of a complicated segregation pattern in meiosis I. Barbara McClintock who did an awful lot of ground-breaking research also early demonstrated that not only can a gene jump into another position but a different position can also change its expression. So when these changes occur in nature – things usually happen. The parts of the article referred to in this thread is rubbish.

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  • 14
    Scott Werden says:

    I am not sure anyone here really understands the issue being raised by the OP. Nobody seems to have answered the question. Here is what I think the issue is:

    Chimps have 24 chromosomal pairs and H. sapien has 23. We know there is a common ancestor between us, or at least that is a result of believing Darwinian evolution. The Korean biologist has cast doubt on whether this it is possible for speciation to occur in which the parent species has one chromosome count, and the new species has a different count. Because a change in chromosomal count is a very discrete change and not gradual (you either have 23 or 24) it would have to occur in a single generation which raises question of what is the mechanism for that? I can see his point but I don’t know enough biology to say what the resolution is.

    Here is an example scenario. Assume an offspring (“Joe”) has parents with 24 chromosomal pairs. A mutation occurred (I think it had to have happened in the gamete that spawned Joe) such that Joe has 23 chromosomal pairs. Joe reaches sexual maturity and meets Jane. Jane is still part of the parent species so has 24 chromosomes. Joe and Jane mate. What happens? Is it successful? And if so, how many chromosomes do their offspring have? It seems that it would be 24 since that is what Jane had and she is the source of the ova that became the offspring. But what role does Joe’s sperm play in determining chromosome count? What happens if Jane has the mutation and has 23 chromosomes and Joe had 24 – is the outcome different?

    At any rate, I am out of my element in answering this, but I believe the Korean fellow does not think that Joe and Jane can mate and produce offspring with the new (23) number, regardless of whether it is Joe or Jane with the 23 chromosomes.

    I suppose there is one more scenario in which Jane and Joe both have the mutation in their gametes, so each has 23 while their parents all have 24 chromosomal pairs. They just happen to meet and successfully breed. This seems rather unlikely if the population is large, unless the mutation to 23 chromosomes is common, and there are lots of Joes and Janes running around with 23 chromosomes.

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