Why did some primates keep their tails, while humans and apes didn’t? Tail loss is thought to be part of the backstory for humans evolving to be bipedal, but precisely how we lost our tails is a question that scientists have long sought to answer.
Recently, researchers uncovered a genetic clue about why humans have no tails. They identified a so-called jumping gene related to tail growth that may have leaped into a different location in the genome of a primate species millions of years ago. And in doing so, it created a mutation that took our tails away.
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As it happens, humans DO still have tails — when we’re embryos. Tails are a trait that can be traced back to Earth’s first vertebrates, so when human embryos develop, we briefly have tails — vertebrae included — during the earliest stages of our growth, as do all animals with backbones. But after about eight weeks, most embryonic human tails completely disappear. They are lost through a process known as apoptosis…. After that, the only remnant of these lost tails in humans is about three or four vertebrae that form the coccyx, or tailbone.
