# Tails and half tails on human (ancestors) **URL:** \ **Category:** Factual Questions\ **Tags:** science-math\ **Created:** [January 25, 2026, 3:30pm UTC](https://boards.straightdope.com/t/tails-and-half-tails-on-human-ancestors/1027006 "2026-01-25T15:30:54Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [January 25, 2026, 3:30pm UTC](https://boards.straightdope.com/t/tails-and-half-tails-on-human-ancestors/1027006/1 "2026-01-25T15:30:54Z")
So humans split from the lineage that produced chimpanzees and bonobos—our closest living relatives—around 7–9 million years ago. Would we have been tail-less at that time? I’m assuming that losing tails was a gradual evolutionary process. My question is, are there any fossils with ‘half tails’? I would think that losing tails completely would have taken a long while. ---
**Author:** ![What\_Exit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/what_exit/32/10652_2.png) [@What\_Exit](https://boards.straightdope.com/u/What_Exit)\ **Post date:** [January 25, 2026, 3:37pm UTC](https://boards.straightdope.com/t/tails-and-half-tails-on-human-ancestors/1027006/2 "2026-01-25T15:37:19Z")
We split from the Ape line after tails were lost. It was only 6-8 million years ago we split off. Tails were lost to our ape ancestors somewhere between 25 and 33 million years ago. ---
**Author:** ![Elmer\_J.Fudd](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmer_j.fudd/32/1211_2.png) [@Elmer\_J.Fudd](https://boards.straightdope.com/u/Elmer_J.Fudd)\ **Post date:** [January 25, 2026, 3:45pm UTC](https://boards.straightdope.com/t/tails-and-half-tails-on-human-ancestors/1027006/3 "2026-01-25T15:45:24Z")
Apparently, the loss was immediate for any primate with the mutated _TBXT_ gene. Mom might have a tail, but baby (and perhaps his offspring) would have no sign of one. I wonder if that is a genetic abnormality found in the occasional modern monkey. ---
**Author:** ![Moriarty](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/moriarty/32/49_2.png) [@Moriarty](https://boards.straightdope.com/u/Moriarty)\ **Post date:** [January 25, 2026, 4:03pm UTC](https://boards.straightdope.com/t/tails-and-half-tails-on-human-ancestors/1027006/4 "2026-01-25T16:03:23Z")
The coccyx is a vestigial tail, correct? ---
**Author:** ![thorny\_locust](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thorny_locust/32/431_2.png) [@thorny\_locust](https://boards.straightdope.com/u/thorny_locust)\ **Post date:** [January 25, 2026, 4:11pm UTC](https://boards.straightdope.com/t/tails-and-half-tails-on-human-ancestors/1027006/5 "2026-01-25T16:11:36Z")
Humans have a tail in early development in the womb. Occasionally somebody’s born with one; though if so there’s often something wrong with their spine. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [January 26, 2026, 5:57pm UTC](https://boards.straightdope.com/t/tails-and-half-tails-on-human-ancestors/1027006/6 "2026-01-26T17:57:25Z")
> [@Elmer\_J.Fudd](#): > > Apparently, the loss was immediate for any primate with the mutated _TBXT_ gene. Mom might have a tail, but baby (and perhaps his offspring) would have no sign of one. That’s pretty wild. And hard to believe that if tails were such a hinderance, why they lasted as long as they did. So are all tail-less apes descendants of that first genetic mutation? Are there other examples of major mutations happening that fast? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 26, 2026, 6:29pm UTC](https://boards.straightdope.com/t/tails-and-half-tails-on-human-ancestors/1027006/7 "2026-01-26T18:29:43Z")
Species who have tails use them for a wide variety of different purposes, and usually the use one species has for them is completely absent for other species. So there are probably also plenty of tails in the animal kingdom that just don’t really have any particular use at all. In such a species, if a mutation happens to arise that results in no tail, there’ll be no particular selective pressure, and the prevalence of the trait will just do a random walk. It might be that, by chance, you get an isolated population that all happens to be tailless (maybe because they’re all descended from a few individuals that happened to be tailless, and who had other worthy qualities that led to that line being prominent), and it might be that, by chance, one of those populations happens to face conditions that lead to speciation. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [January 30, 2026, 8:30pm UTC](https://boards.straightdope.com/t/tails-and-half-tails-on-human-ancestors/1027006/8 "2026-01-30T20:30:58Z")
> [@Lucas\_Jackson](#): > > So are all tail-less apes descendants of that first genetic mutation? To answer my own question, I watched a video on human evolution that did claim that all tailless apes descended from that one, first genetic mutation. > [@Elmer\_J.Fudd](#): > > Apparently, the loss was immediate for any primate with the mutated _TBXT_ gene. Yep… or so the ‘science’ video I watched contends.