
Evolutionary tension between larger brains and smaller pelvises in humans - CapitalistCartr
http://nautil.us/blog/why-are-you-so-smart-thank-mom--your-difficult-birth
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euyyn
> If women’s pelvises were any bigger, they would not be able to walk and run
> well.

That picked my interest so I dug deeper. The author cites p.252 of Brockman's
"What is your dangerous idea?", which is an essay by Prof. Timothy Taylor
called "The Human Brain is a Cultural Artifact". Sadly, even though its topic
is indeed human brains and pelvises, the essay says nothing of the sort. So
Prof. Davies made up the claim, or misattributed the citation and didn't check
it.

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Mz
Women get 4-6x the knee injuries men get, so _something_ is undermining our
ability to walk and run.

[http://oregonstate.edu/ua/ncs/archives/2012/apr/knee-
injurie...](http://oregonstate.edu/ua/ncs/archives/2012/apr/knee-injuries-
women-linked-motion-nervous-system-differences)

[https://www.eurekalert.org/pub_releases/2016-03/uotm-
waw0318...](https://www.eurekalert.org/pub_releases/2016-03/uotm-
waw031816.php)

[https://www.google.com/url?sa=t&source=web&rct=j&url=http://...](https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.ucdenver.edu/academics/colleges/medicalschool/departments/Orthopaedics/clinicalservices/sportsmed/Documents/WISH_SPORTSMED_Female%2520Knee%2520Injuries%2520and%2520ACL.pdf&ved=0ahUKEwjF08a_wIHRAhUB7SYKHdJ0A_YQFgg9MAc&usg=AFQjCNFhUTurlVSeFsoSJEfrpjXvcEafsQ&sig2=Z6u3fOim74Cchcwt2q8Swg)

~~~
Benjamin_Dobell
I wonder how much that is attributed to difference in behaviour.

4-6x is a _huge_ difference (assuming that's accurate) so it's unlikely all of
that could be behavioural. However, high heel shoes and hand-bags are known to
cause lots of posture-related issues.

In Australia, young women also tend to play different sports. For example,
Netball, which is notoriously strenuous on knees and ankles.

~~~
Mz
There may be exacerbating behavioral differences, but my sons tell me women
have greater lower body strength than men. Based on what I have heard about
Chinese foot-binding and how it impacted female musculature, I strongly
suspect this increased lower body strength is related to the skeletal
differences between men and women.

I also have serious health problems that cause belly bloat. As I get that
under control, it has an impact on my hips and that always causes me knee
discomfort (especially at night, trying to find a comfortable sleep position)
during the time that the entire leg structure realigns. So my firsthand
experience suggests that hip structure significantly impacts the knees.

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ars
Summary:

Because we have big heads relative to pelvis size.

Also mentioned is a conjecture that this means there isn't any extra room for
preprogrammed behaviors, so all our intelligence is of the flexible type,
which is why we are smart.

~~~
devoply
We have lots of pre-programed behavior. It's just that it's not conscious.

~~~
woodandsteel
But it is a far smaller part of our whole behavioral repertoire than it is for
other apes. As the article explains, humans differ in having a far greater
ability to learn. Think, for instance, how a gorilla can learn only a few
hundred symbolic words, whereas a human can learn tens of thousands.

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jessriedel
The author suggests that learning rather than hard-coding info in the brain
allowed smaller brain size at birth, but does he cite any evidence or is it
just speculation? It's not at all obvious to me.

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trhway
evolution is getting help, at least in the veterinary area - for "big headed"
dog breeds the C-section has pretty much became the norm.

It also seems to be an interesting evolutionary adaptation that small male
dogs seem to be disproportionally well-endowed to supposedly more easy and
naturally mate up-the-size instead of down-the-size as the former leads to
easier birth than a significantly mismatched latter would.

~~~
dexwiz
I think there is something here about male to female size ratio in breeding
pairs, but I am having a hard time deciphering it.

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partycoder
Humans are technically born ahead of time, and finish development after birth.

If you touch a baby's head you will see that the skull is not fully solid yet.
They're also more fragile than other species. e.g: Horses are born and quickly
start running.

This is because a baby with a fully developed head could not pass the birth
canal.

~~~
erroneousfunk
I wouldn't say _any_ other species. Kangaroos, for instance give birth to
veritable fetuses:
[https://youtu.be/2lCKc8tURtc?t=38s](https://youtu.be/2lCKc8tURtc?t=38s)

Sure, I might be stretching your premise a little bit, but my point stands
that evolution has a very, very wide array of tricks, and humans absolutely
don't have the most underdeveloped young of any species.

