error in code for jaw muscles makes big brains possible?

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I saw something really cool on PBS last night.  I think it was Nova (I was really tired, and came in in the middle of the show).

A doctor whose two brothers had/have muscular dystrophy is looking for the cause, so he can look for a cure.  He looks for any anomalies in genes that affect muscle formation.

He found an error in his own genetic code.  Half of one rung in the DNA "ladder" was missing.  He checked everyone else in his lab, and discovered that everyone had the same error.  All the humans he checked had the error.  He then checked chimp DNA.  That rung in the ladder of chimp DNA is whole.

It turned out that this error, common to all humans, is in the muscles that close our jaws.

Chimps, gorillas, orangutans, and others, all have MUCH stronger jaw muscles than we have.

The doc on the program last night said that the muscles that close gorilla jaws are like human quadriceps.  !!!  As he put it:  "Not biceps, not triceps, *quadriceps*."  Muscles the size of the ones on the tops of our thighs, which lift our legs for every step we take, close gorilla jaws.  [Pausing for a moment to take that in.  Wow.  That is some seriously powerful biting/chewing potential!  Now back to our regularly-scheduled narrative.]

Muscles which close jaws are fastened to skull bones.

Bones get stronger when force is applied to them.  Being strong enough to hold muscles as powerful as quadriceps takes some serious bone.

Skulls are formed from many bones.  Infants are born with unfused skulls (making their heads more flexible, to tolerate birth, for one thing).  Unfused skulls allow heads to grow, which accommodates growing brains.......

Chimp, gorilla, and orang skulls fuse when they are children -- 3-5 years old.

Human skulls fuse when they are adults -- up to age 30.

Late skull fusion makes it possible for brains to continue to grow and grow.....................

Wouldn't it be something, if one of the main reasons we are different from others on this planet is that we have a error in the DNA that makes our our jaw muscles, which causes weaker jaw muscles, which lets us have weaker skull bones, which lets our skulls stay unfused and flexible longer, so our heads can grow for decades, so we can have very big brains?

Wow.

I love PBS.................................

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