this post was submitted on 05 Jul 2024

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Today I Learned

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TIL about de la Chapelle syndrome where people with XX chromosomes are born with traditionally masculine organs & presentation. Usually those with the trait are unaware they have XX chromosomes at all (en.wikipedia.org)

submitted 2 years ago* (last edited 2 years ago) by usernamesAreTricky@lemmy.ml to c/til@lemmy.world

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[–] givesomefucks@lemmy.world 11 points 2 years ago (2 children)

A giraffe has a vein or nerve that goes all the way up to its head for zero reason.

It's incredibly inconvenient and difficult, but it wasn't before their necks were absolutely stupid.

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[–] emmeram@lemm.ee 27 points 2 years ago (3 children)

That would be the laryngeal nerve. It’s been with us vertebrates for a long time.

I take your, “for zero reason,” to indicate that it’s silly that it’s so long in a giraffe. And it is, because it connects the larynx and the brain, two bits that aren’t very far apart. You’d never design it that way from scratch.

But the laryngeal nerve’s length has a reason: it loops around the heart and it developed in our fish-like ancestors. At that time, it wasn’t silly for the nerve to wrap around the heart, because fish don’t have necks and thus the nerve was about the same length whether it wrapped around the heart or not. As necks developed, evolution found it easier to lengthen the nerve than to reroute it. So here we and giraffes both exist, having much longer laryngeal nerves than you’d engineer if you were making us from scratch.

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