5 ms·

Evolutionary tension between larger brains and smaller pelvises in humans

ars 10y ago
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 10y ago
  We have lots of pre-programed behavior. It's just that it's not conscious.
  - woodandsteel 10y ago
    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.
partycoder 10y ago
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 10y ago
  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.
- restalis 10y ago
  Those two types of organisms you talk about actually have names: https://en.wikipedia.org/wiki/Nidifugous https://en.wikipedia.org/wiki/Nidifugous and https://en.wikipedia.org/wiki/Nidicolous https://en.wikipedia.org/wiki/Nidicolous
euyyn 10y ago
> 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.
- Mz 10y ago
  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-injuries-women-linked-motion-nervous-system-differences http://oregonstate.edu/ua/ncs/archives/2012/apr/knee-injurie... https://www.eurekalert.org/pub_releases/2016-03/uotm-waw031816.php https://www.eurekalert.org/pub_releases/2016-03/uotm-waw0318... 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 https://www.google.com/url?sa=t&source=web&rct=j&url=http://...
  - Benjamin_Dobell 10y ago
    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 10y ago
      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.
trhway 10y ago
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 10y ago
  I think there is something here about male to female size ratio in breeding pairs, but I am having a hard time deciphering it.
jessriedel 10y ago
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.

ars 10y ago

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 10y ago
We have lots of pre-programed behavior. It's just that it's not conscious.
- woodandsteel 10y ago
  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.

partycoder 10y ago

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 10y ago
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.
restalis 10y ago
Those two types of organisms you talk about actually have names: https://en.wikipedia.org/wiki/Nidifugous https://en.wikipedia.org/wiki/Nidifugous and https://en.wikipedia.org/wiki/Nidicolous https://en.wikipedia.org/wiki/Nidicolous

euyyn 10y ago

> 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.

Mz 10y ago
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-injuries-women-linked-motion-nervous-system-differences http://oregonstate.edu/ua/ncs/archives/2012/apr/knee-injurie... https://www.eurekalert.org/pub_releases/2016-03/uotm-waw031816.php https://www.eurekalert.org/pub_releases/2016-03/uotm-waw0318... 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 https://www.google.com/url?sa=t&source=web&rct=j&url=http://...
- Benjamin_Dobell 10y ago
  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 10y ago
    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.

trhway 10y ago

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 10y ago
I think there is something here about male to female size ratio in breeding pairs, but I am having a hard time deciphering it.

jessriedel 10y ago

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.