(classical music)
- Heads or tails?
As far as appendages go,
tails are pretty much amazing.
Over time, different animals have
evolved various highly specialized tails.
A horse uses its tail to
swat flies, for instance,
while a bird uses its tail to steer
during flight, which leads
us to today's question.
If these specialized limbs are
so useful, why don't humans have them?
Why don't people, you, me,
David Hasselhoff, have tails?
Well, there are two answers.
First, we don't really need them.
In many quadrupedal, or
four-legged creatures
like cat for example, a
tail helps with balance.
Fish and marine mammals,
on the other hand,
or on the other fin I guess, use their
tails for steering or locomotion.
Some lizards and primates use their
prehensile tails to grip
things, while crocodiles
store fat in their tails kind of similar
to the way camels store fat
reserves in their humps.
But let's look at humans.
We're bipedal, meaning
we walk on two legs,
so our center of gravity passes vertically
down our spine so we don't need a tail
to counterbalance the weight of our heads.
And, unlike some other
primates, we don't need a tail
to help us hold onto things while we swing
through the trees because
as a species, we don't
regularly Tarzan our way
around the forest anymore.
Which is a little
unfortunate, if you ask me.
And why have a tail if you don't use it?
It's just another thing that takes
energy from the rest of the body.
But here's the second answer.
Our ancestors did have tails and
at some point, you had a tail, too.
Each of us has a coccyx, or tailbone,
made of fused vertebrae.
In other primates, this
coccyx leads to the tail,
but again, we don't really need it.
It's a vestigial organ.
I know what you're saying.
"Come on Cristen, I may not be a doctor,
"but I'm pretty sure I don't have a tail."
All mammals have a tail at
some point in development.
When you were about 30
days old in the womb,
you had a tail-like structure
sprouting out of your body.
If you were like most people, you
reabsorbed the structure as you developed.
Now, it's extremely rare, but a few
modern people have been
born with actual tails.
This is what's called an atavism.
A trait of distant ancestors
that reappears in modern day.
Now usually, these tails are just a few
centimeters long and often are
removed shortly after birth.
And that's all there is to the tale.
Come on guys, who writes this stuff, ugh!
Anyhoo, thanks for watching.
Do you think tails are cool?
Would you want one?
Do you have one?
Let me know in the comments,
and be sure to like and
subscribe so you don't miss
a moment of Brain Stuff.
(makes explosion sound)
