Researchers led by Yoav Gilad, an assistant professor of genetics at the University of Chicago, looked at the expression of 1,056 genes in liver samples taken from four primates (humans, the orangutan, chimpanzee and rhesus macaque monkey), representing about 70 million years of evolution.
Sixty percent of these genes — mainly involved in basic cellular processes — are pretty much unchanged in their expression patterns.
The big difference was in a group of genes for transcription factors, important genes that control the expression of other genes.
Hominids split with chimps, the last break in the common primate lineage, around five million years ago.
Since then, transcription-factor genes among humans are four times likelier to have changed expression patterns as the genes they regulate, the researchers found. But there was no such change among the other primates.
"The big question is why are humans so different?" asked Gilad. "What sort of changes in the environment or lifestyle would drive such a rapid shift in the expression of genes — in this case the liver — in humans and no other primate?"
Gilad speculates that the answer could lie in the acquisition of fire, one of the fundamental differences between humans and animals.
"No other animal relies on cooked food," said Gilad. "Perhaps something in the cooking process altered the biochemical requirements for maximal access to nutrients, as well as the need to process the natural toxins found in plant and animal foods."
The idea that gene expression, rather than the raw number of genes, could explain the differences between primates was first aired in 1975, but until now, lack of technology prevented the theory from being taken further.
Name: Chimpanzee (
Pan troglodytes)
Primary Classification: Hominidae (Great Apes and Humans)
Location: Equatorial Africa
Habitat: Savanna, woodlands, swamps and rainforest.
Diet: Fruits, leaves, seeds, bark, honey, ants, termites and occasionally meat.
Size: Averages 3 to 5 ft in height and 100 to 175 lbs in weight.
Description: Black or brown hair; hairless face that turns dark with age; bulging eyebrows; protrusive lips; very long arms; opposable thumbs and big toes; males have large canines; no ail.
Cool Facts: It is one of the only animals that uses tools, such as a twig that it pokes into termite nests and removes when covered in insects. It is our closest relative, sharing about 98 percent of our genes.
Conservation Status: Endangered
Major Threat(s): Habitat loss and poaching
What Can I Do?: Visit
The Jane Goodall Institute for information on how you can help.
