|Joe, you're right that powers of conceptual thought would be self-reinforcing (that was point 5 of my previous post), but you're wrong when you say:|
"If they cause the mutation, that might be one thing. However, it requires them not only to notice the larger brain structures of their offspring, and make the connection that it had to do with eating brains,"
Joe, it's not necessary that "they cause the mutation" (it's only necessary that, by chance, they've taken to eating certain foods THAT WOULD WELCOME such a mutation).
Here's the other side of it for a more global understanding: If they had kept the plant-dominant diet of chimps and gorillas, any chance mutations for increased brain size would be selected against (Big Brains need big fuel and big fat - which plants don't provide) as THEIR gene-planned, larger brain would be semi-starved into disorder before gene expression could be capitalized.
With this in mind, it does not "require[s] them not only to notice the larger brain structures of their offspring, and make the connection that it had to do with eating brains," (unplanned, natural variations in diet explain it all).
As to your question of where the evidence points, below are some relevant excerpts ...
Erren TC, Erren M. Can fat explain the human brain's big bang evolution?-Horrobin's leads for comparative and functional genomics. Prostaglandins Leukot Essent Fatty Acids. 2004 Apr;70(4):345-7.
" ... key mutations which differentiate us from Neanderthals and from great apes are in the genes coding for proteins which regulate fat metabolism, and particularly the phospholipid metabolism of the synapses of the brain."
Folley BS, Doop ML, Park S. Psychoses and creativity: is the missing link a biological mechanism related to phospholipids turnover? Prostaglandins Leukot Essent Fatty Acids. 2003 Dec;69(6):467-76.
"Expanding upon Horrobin's theory that changes in brain size and in neural microconnectivity came about as a result of changes in dietary fat and phospholipid incorporation of highly unsaturated fatty acids, we propose a theory relating phospholipase A2 (PLA2) activity to the neuromodulatory effects of the noradrenergic system. This theory offers probable links between attention, divergent thinking, and arousal through a mechanism that emphasizes optimal individual functioning ... "
Cunnane SC, Crawford MA. Survival of the fattest: fat babies were the key to evolution of the large human brain. Comp Biochem Physiol A Mol Integr Physiol. 2003 Sep;136(1):17-26.
"Human babies have brains and body fat each contributing to 11-14% of body weight, a situation which appears to be unique amongst terrestrial animals."
"The triple combination of high fuel demands, inability to import cholesterol or saturated fatty acids, and dependence on docosahexaenoic acid puts the mammalian brain in a uniquely difficult situation compared with other organs and makes its expansion in early humans all the more remarkable."
Kuliukas A. Wading for food the driving force of the evolution of bipedalism? Nutr Health. 2002;16(4):267-89.
"Here, a new empirical study of captive bonobos found them to exhibit 2% or less bipedality on the ground or in trees but over 90% when wading in water to collect food. The skeletal morphology of AL 288-1 ("Lucy") is shown to indicate a strong ability to abduct and adduct the femur. These traits, together with a remarkably platypelloid pelvis, have not yet been adequately explained by terrestrial or arboreal models for early bipedalism but are consistent with those expected in an ape that adopted a specialist side-to-side 'ice-skating' or sideways wading mode."
Broadhurst CL, Wang Y, Crawford MA, Cunnane SC, Parkington JE, Schmidt WF. Brain-specific lipids from marine, lacustrine, or terrestrial food resources: potential impact on early African Homo sapiens. Comp Biochem Physiol B Biochem Mol Biol. 2002 Apr;131(4):653-73.
"The polyunsaturated fatty acid (PUFA) composition of the mammalian central nervous system is almost wholly composed of two long-chain polyunsaturated fatty acids (LC-PUFA), docosahexaenoic acid (DHA) and arachidonic acid (AA). PUFA are dietarily essential, thus normal infant/neonatal brain, intellectual growth and development cannot be accomplished if they are deficient during pregnancy and lactation. Uniquely in the human species, the fetal brain consumes 70% of the energy delivered to it by mother."
"Homo sapiens is unlikely to have evolved a large, complex, metabolically expensive brain in an environment which did not provide abundant dietary LC-PUFA. Conversion of 18-carbon PUFA from vegetation to AA and DHA is considered quantitatively insufficient ... "
"At South African Capesites, large shell middens and fish remains are associated with evidence for some of the earliest modern humans. Cape sites dating from 100 to 18 kya cluster within 200 km of the present coast. Evidence of early H. sapiens is also found around the Rift Valley lakes and up the Nile Corridor into the Middle East; in some cases there is an association with the use of littoral resources. Exploitation of river, estuarine, stranded and spawning fish, shellfish and sea bird nestlings and eggs by Homo could have provided essential dietary LC-PUFA for men, women, and children without requiring organized hunting/fishing, or sophisticated social behavior. It is however, predictable from the present evidence that exploitation of this food resource would have provided the advantage in multi-generational brain development which would have made possible the advent of H. sapiens."