The "bottom line is that this study underlines the risks of making generalizations about human evolution," said Ajit Varki, a professor of cellular and molecular medicine at the University of California at San Diego.
"Humans only emerged once, after many complex stages of hominid evolution, and there is no reason to assume that the most logical explanations (for our evolution) will actually turn out to be right," he added. "And the final answers are likely to be far more complex than we currently think they are."
The new study is hardly the last word on the matter, said Varki. There are many ways genes can come and go, and affect evolution.
"In the end there will be no substitute for looking into the details of each gene difference from the functional perspective," said Varki. "It could well turn out that the deletion of a specific gene or a single critical amino acid encoding change in a gene has more biological significance than a large number of genes that at first glance seem to have undergone a lot of changes."
