How humans lost our tails

I find it unfair that humans don't have tails but monkeys do. More than 60 million years ago, the earliest primates did have tails that helped them not fall out of trees. Most primates still have tails but people and other apes lost them along the way. All we have is a pathetic little coccyx. What the hell happened to our tails? Biologists at NYU's Grossman School of Medicine have now identified the genetic mutation that shortchanged us. To test their hypothesis that a spontaneous mutation in a gene called TBXT was responsible, they genetically engineered mice with that mutation. "When these embryos developed, many of the animals failed to develop a tail," writes Carl Zimmer in the New York Times. "Others only grew a short one." Still, while the scientists have uncovered how we lost our tails, the why remains a mystery.

From the New York Times:

The first apes were bigger than monkeys, and their increased size would have made it easier for them to fall off branches, and more likely for those falls to be fatal. It's hard to explain why apes without tails to help them balance wouldn't have suffered a significant evolutionary disadvantage.

And losing a tail could have brought other dangers, too. Mr. Xia and his colleagues found that the TBXT mutation doesn't just shorten tails but also sometimes causes spinal cord defects. And yet, somehow, losing a tail proved a major evolutionary advantage.

"It's very confusing why they lost their tail," said Gabrielle Russo, an evolutionary morphologist at Stony Brook University in New York who was not involved in the study. "That's the next outstanding question: What on earth would the advantage be?"