My problem with evolution

I have a problem with the theory of evolution, which I was going to bring up in my last post, but I was revising for my exam I had this afternoon (it went quite well, thanks for asking), so I left it until today.

Yes I can hear all you creationists out there, “what’s that you say? A secular humanist doubting evolution? This is surely evidence that we were right all along!” Well screw you all, that’s not what I’m saying. Let me explain my problem.

The issue was brought up by Dr Marc Surtees of the Edinburgh Creation Group during a post-talk discussion. We’re all agreed that small changes through reproduction and mutation, combined with natural selection over a long period of time is why species are different from each other today. Now one difference between species is that they often have different numbers of chromosomes. My problem is how this comes about through mutation and natural selection.

So I’m sure you’re all aware of the similarity in chromosomes between chimps and humans, and that it appears that two of the chimp chromosomes at one point fused together to form one of the modern human chromosomes, I believe it’s the 2nd, but I could be mistaken so don’t quote me. Anyway someone brought up this remarkable similarity, and the fusion, as evidence that humans and chimps are related, but Dr Marc turned the conversation around and showed how this is one of the greatest arguments against evolution.

The way evolution works with mutation, means that at some point one individual human ancestor must have had a mutation which meant the 2 chromosomes that we still find in chimps fused into the one we now see in the modern human. You can’t have half a chromosome, so it must have happened in one stage. Now we have one individual with 23 chromosomes, and all the rest of his/her species has 24. How does s/he reproduce? You need the same number of chromosomes as your mate to produce fertile offspring. How does this mutation get passed on?

Now I was going to email some experts and ask them (if I can find Dawkins’ email on RDF I’ll probably ask him too, hehe), but it appears I’ve already found the answer. Once again it seems the creationist camp has been very short sighted again (either that or Dr Marc was lying, but it looks like other people have made the same mistake). The reason people think you need the same number of chromosomes to reproduce fertile offspring is because of the well known example that if you cross a horse with a donkey, you get a mule, which is infertile. Apparently this isn’t true across the board as creationists seem to think. This article says (a third down the page, paragraph starts “some may raise the objection”), that a Przewalski’s Wild Horse, the closest wild relative of the domesticated horse, has 66 chromosomes, in comparison with the 64 of the domesticated horse, but they can produce fertile offspring. I’d be interested in finding out more about the genetic make-up of the offspring though. So it’s not such a problem.

I think I’m still going to email around anyway, just in case there’s another explanation.

Listening to: Coheed and Cambria – Blood Red Summer

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7 Responses to My problem with evolution

  1. Clare says:

    My flatmate and I were just mulling this one over and then we remembered Down Syndrome. This would be an example among the human population of the presence of an extra or partial extra chromosome. According to a wikipedia article, there is reduced fertility in men and women with Down Syndrome, but still known cases of men with Down Syndrome fathering children. Unfortunately, we can’t seem to find the references the article is referring to.

  2. grammarking says:

    Hey, thanks for the link btw.

    Yeah I was discussing it with a medic friend in the pub and that same example of Down’s Syndrome popped into my head from GCSE biology all those years ago. He reckons that the majority of chromosome-mutants would in fact be able to reproduce properly with the rest of the species. There is a problem with the reduced fertility of Down’s Syndrome though, because if there was any negative effect of the extra chromosome mutation it would be erased from the gene pool by natural selection. Which is presumably why Down’s Syndrome is a disorder rather than the norm.

    In any case I’ve emailed a few professors and found some examples online, maybe in response the whole meiosis process will be explained, which would be good.

  3. myrmecos says:

    This might help: There are gibbons where different members of the same, interfertile population have different chromosome arrangements. As long as homologous stretches of DNA can still pair up during cell division there shouldn’t be a problem.

  4. grammarking says:

    Thanks myrmecos, there seems to be a number of species that can do this, and the lack of chromosome alignment doesn’t seem to be such a problem in cell division. I’d be interested in knowing more about the exact process, if anyone can enlighten me.

  5. Marc Surtees says:

    Hi folks,

    I hope you do not mind if I complain about the suggestion that I might be lying, even creationists are human and cannot get all the information on a subject any faster that your average humanist.

    In fact I had not heard about the Przewalski’s Wild Horse. Thanks to soemone else who came to the meeting I have now read something about this, but do not have the original paper. However, I would like to suggest that while this is interesting I do not think this is conclusive for the human story. There are whole populations of Przewalski’s Wild Horses and domestic horses and their respective chromosome numbers stay the same despite the occasional cross. The hybrid is only fertile when backcrossed with a domestic mare. I would guess is that the offspring have the same number of chromosomes as the domestic horse. So you still have no permanent change in karyotype.

    Marc

  6. grammarking says:

    Hey Marc, thanks for dropping by.

    I certainly didn’t seriously think you were lying and I hope anyone who read it realised that it was just a (probably very poorly expressed) joke. My apologies.

    I really would be interested to find out more about Przewalski’s Wild Horse/Domestic Horse hybrids, as I said, but since the Wild Horse is such an endangered species, it seems not a lot of research has been done on them. I certainly can’t find much online.

    I don’t really see how the fact that they’re only fertile with a domestic mare is a problem, since that’s what I daresay any new genetic mutant would have to be mating with. It’s perfectly plausible to me that the 23 and 24 chromosome ‘species’ (my knowledge of scientific vocab fails me here) could live side-by-side for some considerable time. If the offspring of the mutants do have the same chromosomes as the ‘originals’, that would be a problem, but until we know otherwise I would think it foolish to assume, or guess, that they do.

    Mike

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