Edinburgh Skeptics were delighted to welcome long-term supporter PZ Myers to the Fringe. He decided the title of his original talk was a bit too pompous, and opted to explain instead why creationists’ arguments were wrong (and it wasn’t simply because they all seem to speak in Comic Sans). Along the way, he gave an introduction to genetics, baloney and things that make him laugh.
His talk focused on a specific aspect of genetics which creationists have trouble with. Humans have 23 chromosomes; other apes have 24. This difference arose about 4-6 million years ago, when a species of ape, which was a common ancestor to both humans and chimps, was alive.
At some point, when a particular ancestor egg met a particular ancestor sperm, chromosomes ‘2A’ and ‘2B’ fused together chemically, resulting in a slightly mutated ancestor with a single chromosome ‘2’. This didn’t stop the mutant ancestor (or ‘proto-human’, as we might think of it) from having offspring of its own, and the mutation spread, becoming more and more frequent in the population. (Mutations don’t necessarily result in infertile offspring; at worst, merely a reduced chance of producing healthy sperm and eggs.)
Creationists don’t like this.
They say that the chemical signature of telomeres (the bits at each end of a chromosome) from the ancestors’ 2A and 2B should be found in the middle of a human chromosome 2, but there isn’t enough of it there – overlooking the fact that there’s no survival benefit this signature to be passed on, so after 4 million years you’d expect it to be somewhat degraded. In fact, creationists never explain what it is they expect to see, so they never produce any hypotheses to prove or disprove.
Creationists also overlook the fact that there’s hardly any shuffling of genes between chimps and humans; the genetic codes are extremely similar, suggesting that they parted evolutionary ways quite recently – especially compared to mice (70 million years ago) or sushi (400 million years ago). Sticking to human chromosome 2, the rest of the chemical signature matches perfectly with chimp chromosomes 2A and 2B. Why do creationists ignore this? Why concentrate on the remnants of telomeres in the middle?
As Myers explained, it was as if there had been a car crash, and most people looking at it would identify it as such. But creationists would focus on a tiny, mangled scrap of wreckage and declare that because they can’t identify it as any part of a car, there couldn’t have been any cars involved at all.
Audience questions, whether from the layperson or informed student, were all thoughtful and perceptive. Is there a genetic ‘threshold’ which decides whether or not we are human? (No; genetics and chromosomal errors say nothing of our humanity.) Is there evidence of centromeres in chromosomes 2A and 2B matching anything in chromosome 2? (It’s more ambiguous because the chemical signature of centromeres, in the middle of each chromosome, is not as distinct as the telomeres found at the ends). Were there ever humans with chromosomes 2A and 2B? (They didn’t just vanish immediately; they were just less likely to have offspring and became less frequent in the population with each generation.)
Thanks to Professor Myers for providing an accessible and informative talk, and for staying to talk with people in the bar long afterwards; and thanks to the staff at the Banshee Labyrinth for opening up an extra room for our overflowing audience to see the talk via video feed.
NB: any errors in this write up are mine alone.