The relative age of genetic changes between the human and chimp genomes varies over a period of ~ 4 million years, depending on where in the genome you look. This figure illustrates this concept (note -- these are not actual data points). For example, Gene A first diverged millions of years before Gene B. Of particular note is the X chromosome, which falls almost entirely in the time just before final speciation. Credit: Broad Institute
New study suggests that the last common ancestor shared between chimps and humans may be ~1 million years more recent than previous estimates. Additional findings reveal a particularly young age of one of the human sex chromosomes and point to a complex process of speciation, with possible interbreeding during speciation.
The evolutionary split between human and chimpanzee is much more recent – and more complicated – than previously thought, according to a new study by scientists at the Broad Institute of MIT and Harvard and at Harvard Medical School published in the May 17 online edition of Nature.
The results show that the two species split no more than 6.3 million years ago and probably less than 5.4 million years ago. Moreover, the speciation process was unusual – possibly involving an initial split followed by later hybridization before a final separation.
[..]