B2 中上級 2031 タグ追加 保存
[bird chirp]
Look down. No matter what your biological sex, I'm willing to bet most of you have
two nipples. If you can't see them, they're probably under your shirt.
Some people have even more than two! But that's for another video.
It's easy to see why females have two nipples.
We're mammals. It's right there in the name.
Dogs, cats, pigs and whales all have nipples too. Like us, they nourish their offspring with milk.
Male nipples?
Not much going on there.
If they're not an evolutionary advantage, why hasn't natural selection erased them?
Because my nipples are cheap, and they're not hurting anything.
In the eyes of evolution, male nipples don't have much cost: Just a little more tissue.
But deleting them from the recipe altogether, reprogramming the genes and body development
in just in one sex? That would cost more.
Traits don't have to provide a specific advantage to get passed on.
Why is your blood red and an octopus's is blue? It's not because one color's better,
it's just a side effect of nature selecting different chemistry for different creatures.
And sometimes, traits can end up being used for a function
different from what nature originally selected.
Not every trait is an adaptation, and they don't all have a point.
Sometimes they have two.
Stay Curious.
This video's part of our 12 Days Evolution series.
Check out more by exploring Darwin' beard.
Find the links down description or you could click that things that just pop up on screen.
You know what else doesn't cost much? Click and subscribe.
It's free actually.


Why Do Men Have Nipples? - 12 Days of Evolution #7

2031 タグ追加 保存
Tiffany Yu 2018 年 12 月 9 日 に公開
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