John Mackay responds:
Crabtree is correct about mutations degrading the human genome, and therefore it
is inevitable that some mutations would damage human brain function. Recent
genome studies such as the 1000 Genome Project have shown that genes are being
rendered useless (and therefore effectively lost) or less functional with every
generation. However, no-one has reported a newly formed gene that improves human
intellect (or any other human function). There is, therefore, no evidence
mutations created and “optimised” these genes in any human ancestor, and caused
them to evolve a large complex brain, especially as they are observed to be
doing the opposite!
