From John Hawks: http://johnhawks.net/weblog/reviews/brain/paleo/lynch-granger-big-brain-boskops-2008.html More at: http://johnhawks.net/weblog/reviews/brain/paleo/return-amazing-boskops-lynch-granger-2009.html I got into this while trying to find something of substance from a stray comment about boskop man. From a couple skull fragments found in 1913 Please Register or Log in to view the hidden image! Some people's imaginations went a tad on the wild side. OK The journey(so far) has led to the above quoted from John Hawks. Anyone have supportive evidence of his assertion? in general Your thoughts? potential reconstruction Please Register or Log in to view the hidden image!
It's a standard prediction of Darwinian considerations - childbirth mortality is a severe selection pressure, so is child mortality over a long maturation outside the womb, and if some gain in efficiency or architecture would preserve the intelligence advantage in a smaller package its evolutionary advantage would be very likely decisive.
I think it is. Look at the simplest organisms which are only reactive. Then look at humans who are pro-active due to evolved brain power which allows for more pro-active specialization. The cuttlefish once was a sea-slug. It's evolved brain now makes it relatively one of the most intelligent organisms in the ocean.
In general, my views are similar to the thing you quoted by Hawks. Just in general, phylogenetically and looking at organisms comparatively, organisms with larger brains do tend to be smarter. But it isn't absolutely linear. I've always been struck by the birds, with tiny little heads but very alert and capable of very complex behavior. And with regards to humans, Hawks might be on to something when he points out that brains are expensive in energy and nutrients. So not only would there be selective value in growing the brain, since that would presumably correspond to smarter organisms, there would also be advantage in shrinking the brains as long as that didn't impact intelligence too dramatically. So combining the two contrary imperatives and we might have selective pressures towards an efficiency that can do more with less, so to speak. Some biological equivalent of algorithmic efficiency.
Is it possible that the overall size of the brain has shrunk, but that the surface area has actually increased, i.e. more folds allowing for greater density of neurons. That would accomplish both desired effects of resource and energy management.
I believe this theory as to why brain size reduction has been happening is quite mainstream among biologists. The reduction has been observed continuously since the early 1900’s — the only real conjecture is the question why? I would argue that it’s a variety of factors, specifically in recent history the advancements of agriculture perhaps weren’t as intellectually challenging or maybe the diversity of their diets not as pervasive. Like most patterns of evolution it seems hard to pinpoint exactly the how and the why of it all, but energy consumption and compartmentalization seem most likely.
OK Back at it. So far, there seems to be broad agreement that most of us are experiencing a multi-generational shift to smaller brains. One could go so far as to say that this started with heidelbergensis--with rapid expanse of the cranial cavity for millennia, topping out at 1800 cc then shrinking through neanderthalensis to us. But that is a different subject than the one for this thread. From an average(from extent fossils) of 1650 cc for cromagnon to a modern average of well under 1450 we have lost more than 12% of cranial capacity. Average embraces quit a wide range with a lower limit of 1200cc. [there is no proven 1:1 ratio of brain size to intelligence----the inverse is also true] Ok then: The question of causality comes into play. Many speculations are to be found. What seems most likely(to me) is a 2 pronged hypothesis. 1) We ain't hunter gatherers no more---we have a different diet and different needs. We have a more stable food source and do not have to live by our wits. Diet---we eat more grains and less wild stuff. We eat less protean and more carbs. The grains we eat lead to more inflamation which means that we need to invest more in our immune system to fight inflammation. So being as both the brain and immune system are energy hungry, we rob one to feed the other. Wild fruits and berries and grains have more anti-oxidants per calory than do domesticated crops. So, we need to make up the difference with our immune systems. So we sacrifice feeding a larger brain to accommodate our lower protean lower omega 3 fatty acids in favor of feeding our immune systems. some links: https://www.gwern.net/docs/algernon/1998-henneberg.pdf https://biology.stackexchange.com/questions/44662/brain-capacity-of-cro-magnon-man-vs-modern-man https://www.persee.fr/doc/bmsap_0037-8984_1979_num_6_4_1979 https://www.researchgate.net/public...ion_of_Holocene_populations_in_Northern_China ok If that is true: Where would you expect to see less diminishment of cranial capacity? I would expect to see it where there is less modern diet 2 maps of cranial capacity Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image! Conclusion: We are experiencing a result of exceeding the natural carrying capacity of the land. We have chosen a larger and more stable population in exchange for the evolution that brought us to the genius of cromagnon.
I believe women can more reliably answer that one. When I hear women in 36 hr labor, that just doesn't sound naturally efficient.
one hypotheses as/re the demise of the neanderthals was that the bigger brains made birth more difficult which led to lower birth rates which led to their demise
