One might assume that the differences between chimp and human genes boil down to those sorts of typographical errors: one nucleotide being swapped for a different one and altering the gene it sits in. When the chimp and human genomes are compared, some of the clearest cases of nucleotide differences are found in genes coding for transcription factors. Humans and chimps each have somewhere between 20,000 and 30,000 genes, so there are likely to be nucleotide differences in every single gene. And it’s precisely some of those genes, the ones involved in neural development, that appear on the list of differences between the chimp and human genomes. Indeed, a close look at the chimp genome reveals an important lesson in how genes and evolution
