On Sunday, March 19, 2017 at 2:29:55 PM UTC-5,
Astero...@yahoo.com wrote:
> Interesting question.
As I mentioned earlier, monkeys still have tails.
What you're asking is why *apes* lost their tails. And while I'm not Darwin nor a biologist, I think I have an idea that *may* hold water. Those of
you who know what you're talking about may feel free to correct me.
Most monkey and ape species are primarily forest dwellers, spending most of
their time in the forest canopy (there are exceptions - I think baboons and
gorillas spend most of their time on the ground, although I could be wrong
about that).
Monkeys are quadrapeds - they walk on all fours, both when on the ground and
when moving through the trees. They walk, run, and jump along branches in
the canopy. Viewed in that light, it's easy to see why they've retained
long, powerful tails - it helps provide balance when they're scampering through the branches. Other mammals that do a lot of broken-field running
such as cats (lions, cheetahs) and canids (wolves, foxes) have relatively
long and powerful tails as well. Then you have hoppers like roos and
wallabies - their tails act as counterweights to the rest of their bodies.
Of course, this isn't 100% true - deer, antelope, etc., have small tails
and run like hell. But I think they've figured out different ways of
maintaining their balance that don't rely on a tail.
Apes are brachiators - they swing by their arms from branch to branch. A
tail doesn't help much in that situation, and would more likely just get
in the way. Longer forelimbs result in bigger swings, shortening the tail
and hindlimbs raises the center of gravity and reduces the amount of mass
that has to be supported by the hands. Since their arms are so long
relative to their legs, apes have adopted knuckle-walking for moving along
the ground.
There are plenty of other mammals that either have small or vestigial
tails - heffalumps, bears, sloths, pigs, etc., and they tend to not be
open-field runners either.
So at least part of it comes down to locomotion - mammals that needed to
maintain balance when running flat out on uneven terrain tended to hold
on to their tails. Mammals that didn't do that much running, or tended to
run in straight lines, tended to lose their tails.
Again, not 100% the case, but there are enough examples on both sides that
I feel fairly confident that's at least part of the explanation.