The key genetic differences between humans and chimpanzees must lie in the approximately 1% of protein-coding DNA sequence that differs between the two genomes. What do we see when we compare human and chimpanzee genomes?

A gene that has attracted a lot of interest is FOXP2, a member of a large family of evolutionarily conserved genes that encode transcription factors that play important roles in development. Individuals with mutations in FOXP2 often have difficulty with speech and language. Interestingly, laboratory animals whose FOXP2 has been knocked out also have communication impairments. Songbirds are less capable of learning new songs, and the high-frequency “songs” of mice are disrupted. In addition to its effects on the brain, FOXP2 plays a role in the development of many tissues.

Studies of the gene’s amino acid sequence reveal a pattern of extreme conservation. The sequences in mice and chimpanzees, whose most recent common ancestor lived about 75 million years ago, differ by a single amino acid (Fig. 24.14). However, two amino acids are present in humans but absent in chimpanzees. Studies of Neanderthal DNA have shown that Neanderthals possessed the modern human version of FOXP2. The presence of the same version of the gene in both species suggests that the differences arose in the hominin line before the split between our species and Neanderthals, which occurred at least 600,000 years ago.

FOXP2 gives us a glimpse of the genetic architecture of the biological traits that are likely to be important in the determination of “humanness.” Those two differences in amino acid sequence are intriguing, but they do not a human make. Substitute the human FOXP2 gene into a mouse and you will not get a talking mouse. The critical genetic differences are many, subtle, and interacting.

Quick Check 4 The FOXP2 gene is sometimes called the “language gene.” Why is this name inaccurate?