A new study by University of Leicester researchers reveals that chimpanzees have an ancient common ancestor, also referred to as a genetic "Adam," that lived approximately one million years ago, making them five times older than human beings. The study pinpointed the DNA sequences of a large part of the Y chromosome and the mitochondrial DNA (mtDNA), which are passed down father to son and mother to offspring, respectively, in a set of chimpanzees, bonobos, gorillas and orangutans.
Using this genetic information, the team constructed genealogical trees of each species and subspecies and compared them, leading them to the discovery of the genetic "Adam" that lived one million years ago.
"The ancestor of a Y-chromosome family tree is sometimes called 'Y-chromosomal Adam'. We can compare the ages of 'Adams' between the species," Pille Hallast, lead author of the study, said in a press release. "For humans the age is about 200 thousand years, while for gorillas it's only about 100 thousand years. Thanks to two chimps in our sample, Tommy and Moritz, chimpanzees have an amazingly ancient 'Adam', who lived over 1 million years ago."
He added, "The Y chromosome tree for gorillas is very shallow, which fits with the idea that very few male gorillas (alpha males) father the offspring within groups. By contrast, the trees in chimpanzees and bonobos are very deep, which fits with the idea that males and females mate with each other more indiscriminately."
Furthermore, the comparison of the Y chromosome and mtDNA trees led to the observation that humans have much more in common with gorillas than chimps, suggesting that over a long period of human evolution, we practiced a polygynous system where just a few men mated with most of the women.
"This is more like the gorilla system than the chimpanzee 'multimale-multifemale' mating system," concluded Mark Jobling, the projects leader.
The findings were published in the Feb. 16 issue of Genome Research.
