Posts Tagged I’m so glad I can trust italics-girl never to turn on me
Okay, first things first, I need to check if anybody noticed I haven’t had any internet access from home since last Friday thanks to my ruddy cheap ISP and was therefore unable to post anything last week. No? No-one? Good, good, the perception nanites are working. Moving on…
WARNING: SCIENCE CONTENT
Now, we all know about chromosomes: they’re the things in our cells which hold our genes. Now, all the great apes have 24 pairs of chromosomes. This is fair enough, but (according to evolution) we are just as closely related to the great apes as they are to each other. So we should also have 24 pairs of chromosomes, correct?
But we don’t. Human beings only have 23 chromosome pairs.
Now, this isn’t a massive deal: chromosomal counts differ greatly within genus, and sometimes even within 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). But chromosomes don’t just disappear: when they do, the victim of the mutation is missing a good quantity of, usually important, DNA. So what happened to the 24th human chromosome?
With everything I’ve just told you, a logical prediction can be made: at some point in our ancestry, but not in the ancestry of other great apes, two chromosomes must have joined. This isn’t a harmful mutation: the gene’s themselves are still viable, but they are now part of a single chromosome, not two.
Now, chromosomes have easily recognisable sequences at the ends, called telomeres, and another recognisable type of sequence in the centre called centromeres (0). Centromere’s are where the chromosome divides during reproduction.
Here’s a representation of what I’m talking about, with telomere’s represented by X’s and centromere’s represented by 0’s:
So, geneticists realised that if humans really are descended from apes, one of their chromosomes should have two (X’s) in the middle of it, with a pair of (0’s) flanking them. Keep in mind that if this isn’t found, common ancestry with apes is in big trouble: after all, how else could we lose a chromosome without it screwing us up?
Here’s a abstract representation of Human Chromosome Number 2, as discovered by geneticists who went looking for this pattern as a direct result of the theory of evolution.
“Evolution has made a testable prediction and has passed.”
— Kenneth Miller
No big surprise there if you accept the theory of evolution, but it is a pretty nice piece of evidence nonetheless: easy to understand and rather difficult to refute. If you take a look at the attempts of anti-evolutionist groups like Answers In Genesis (here), you’ll notice they never even try to explain HC2, instead simply asserting it’s not evidence for evolution and then throwing out red herrings and going off on strange tangents about information content. The closest they come to an explanation is a half-hearted admittal that maybe humans and apes were created with the same number of chromosomes. Hooray for ad hoc reasoning, I guess? I’ll let you judge which explanation is more satisfying.
This one I learned from the Dover v Kitzmiller Intelligent Design Trial Transcripts. Kudo’s to Ken Miller, who presented it during the trial. And apologies to the noble geneticists whose work I am simplifying (butchering would perhaps be a better term) to make this point. Please don’t send your armies of genespliced insect-men after me.
Send the insect-men! He still thinks I’m on his side, but he’s gone too far this time. The truth is, he’s just stalling for time to finish building his [OBSCURED BY PERCEPTION NANITES] and I can’t stand by any longer. Those poor porpoises!