By all rights, chimps and humans should be a lot more similar than we are, considering that our DNA sequences are just under 99 percent identical. But as geneticists keep discovering, just as which music you hear depends not only on what you’ve loaded onto your iPod but also on which tunes you actually play, so what matters in DNA isn’t so much which genes you have as which ones are expressed.
Curiously, scientists now report, which genes are expressed depends, at least in part, on what you eat.
We humans eat much more meat and fat than chimps do, and also cook our food. Researchers at the Max Planck Institute for Evolutionary Anthropology in Germany therefore fed laboratory mice different human and chimp diets for two weeks. The mice ate raw fruits and vegetables like chimpanzees in zoos get, or a human diet of food from the Institute cafeteria, or a pure fast food menu from the local McDonald’s.
Result: the different diets led to remarkable changes in which of the mouse genes were turned on, the scientists report this evening in the journal PLoS ONE. There were thousands of differences in the levels at which genes were expressed in the mouse livers but, interestingly, not in the mouse brains. Many of the genes that changed in the mouse livers are known to differ between humans and chimpanzees, suggesting that these differences might be caused by the difference in human and chimpanzee diets.
Obviously what you eat doesn’t determine which species you are (though we know some vegans who are looking a little simian lately). The scientists calculate that diet accounts for expression differences of 4 percent to 8 percent in the mice’s liver genes, whereas the amount of expression difference between humans and chimpanzees is 15 percent. But it is one more clue to how such small genetic differences can produce species are different as chimps and people.