Our oldest animal ancestors had tails. Why not us?

Washington— Our oldest animal ancestors had tails. Why not us? About 20 or 25 million years ago, when apes differentiated from monkeys, our branch of the tree of life lost its tail. Since the times of Charles Darwin, scientists have wondered why—and how—this happened. Now, researchers have identified at least one of the key genetic tweaks that led to this change.

“We found a single mutation in a very important gene,” explains Bo Xia, a geneticist at the Broad Institute and co-author of a study published Wednesday in the Nature magazine. The researchers compared the genomes of six species of apes, including humans, and 15 species of tailed monkeys to determine key differences between the groups.

Once a significant mutation was identified, they tested their theory by using the gene editing tool CRISPR to modify the same point in mouse embryos.

Those mice were born without tails. Xia cautioned that other genetic changes may also influence tail loss. Another mystery: Did not having a tail really help these ape ancestors and, eventually, humans survive? Or was it just a chance mutation in a population that thrived for other reasons? “It could be chance, but it could also have been a huge evolutionary advantage,” says Miriam Konkel, an evolutionary geneticist at Clemson University, who was not involved in the study.