Why humans lost their tails: Scientists provided answer

How the research was conducted

A team of scientists discovered a genetic change shared by humans and monkeys, which caused the ancestors of humans to lose their tails about 25 million years ago.

While most monkeys have tails, hominoid apes and their close extinct relatives lack this appendage. They have a tailbone (coccyx), which is a remnant of vertebrae that form the tail in other animals.

Geneticist Bo Xia from Harvard University in Cambridge, together with colleagues, analyzed 140 genes that influence tail development. Scientists found that these genes underwent thousands of changes during evolution.

In their research, the team of scientists also considered the findings of Ukrainian scientist Nadia Dobrovolska-Zavadska, who described a variety of short-tailed laboratory mice in 1927. The scientist suggested that the mouse had a mutated gene called T - its human equivalent now known as TBXT.

Mice with such mutated genes had short tails or no tails at all.

What the research revealed

In 2021, Bo Xia discovered that the shape of the protein encoded by the TBXT gene in monkeys had shortened due to chemical changes in the organism. Additionally, scientists noticed that mice to which the TBXT gene was added developed many tail-related defects.

According to the assumption of the team of scientists, hominoid apes might have lost their tails because it facilitated bipedal locomotion. Another possible reason is that they spent less time in trees than their ancestors.

However, anthropologist Gabriel Russo from Stony Brook University in New York emphasizes that monkeys are not the only primates without tails. This trait is also absent in lorises, mandrills, and some macaques. This leads scientists to believe that tail loss evolved multiple times.

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