Answer:
The study authors posit that the mutation randomly might have cropped up in a single ape around 20 million years ago, and was passed on to offspring. Perhaps being tailless was a boon to the apes, and the genetic mutation spread like wildfire.
Step-by-step explanation:
Much later, when they evolved into primates, their tails helped them stay balanced as they raced from branch to branch through Eocene jungles. But then, roughly 25 million years ago, the tails disappeared. Charles Darwin first recognized this change in our ancient anatomy.