Evolutionary geneticist Jianzhi Zhang and colleagues at the University of Michigan in Ann Arbor, US, compared DNA sequences for 13,888 genes shared by human, chimp and rhesus macaques.
For each DNA letter at which the human or chimp genes differ from our shared ancestral form – inferred from the corresponding gene in macaques – researchers noted whether the change led to an altered protein. Genes that have been transformed by natural selection show an unusually high proportion of mutations leading to altered proteins.
Zhang’s team found that 233 chimp genes, compared with only 154 human ones, have been changed by selection since chimps and humans split from their common ancestor about 6 million years ago.
Many people probably find these results surprising. Indeed, I suspect many people will simply find it unbelievable or even offensive. But even leaving those people aside, I suspect that most people will be surprised because they see evolution as a progression towards some platonic ideal, some absolute notion of better.
The belief that evolution is a march towards an objective end point is probably due to a mixture of a few things including our own egos i.e. “we’re the best, most evolved, most successful species and everything else is evolving towards being like us, right?” That’s why sci-fi, set in the future, show everyday animals having evolved into furry humans. But the concept is also reinforced by diagrams of the evolutionary tree – which places mammals (and especially humans) at the top of the tree and invertebrates at the bottom.
The trouble is that while the relationship between species can helpfully be represented as branches; the notion of progression from ‘bad’ to ‘good’ from ‘less evolved’ to ‘more evolved’ is also inferred from such diagrams and this is misleading. Sorry, I mean untrue. Humans aren’t better evolved than other species – because better only makes sense from the context of the individual species in a specific niche. Oak trees are best at what they do, where they do it; bacteria species at what they do, and humans at what we do.
So other species, such as chimps, may well be ‘more’ evolved than humans i.e. their DNA has undergone more change; but importantly all species are as equally ‘well’ evolved as each other (and that includes humans) because species are selected by their local environment not against some abstract notion of best.