Our large brain, long life span and high fertility are key elements of human evolutionary success and are often thought to have evolved in interplay with tool use, carnivory and hunting. However, the specific impact of carnivory on human evolution, life history and development remains controversial. Here we show in quantitative terms that dietary profile is a key factor influencing time to weaning across a wide taxonomic range of mammals, including humans. In a model encompassing a total of 67 species and genera from 12 mammalian orders, adult brain mass and two dichotomous variables reflecting species differences regarding limb biomechanics and dietary profile, accounted for 75.5%, 10.3% and 3.4% of variance in time to weaning, respectively, together capturing 89.2% of total variance. Crucially, carnivory predicted the time point of early weaning in humans with remarkable precision, yielding a prediction error of less than 5% with a sample of forty-six human natural fertility societies as reference. Hence, carnivory appears to provide both a necessary and sufficient explanation as to why humans wean so much earlier than the great apes. While early weaning is regarded as essentially differentiating the genus Homo from the great apes, its timing seems to be determined by the same limited set of factors in humans as in mammals in general, despite some 90 million years of evolution. Our analysis emphasizes the high degree of similarity of relative time scales in mammalian development and life history across 67 genera from 12 mammalian orders and shows that the impact of carnivory on time to weaning in humans is quantifiable, and critical. Since early weaning yields shorter interbirth intervals and higher rates of reproduction, with profound effects on population dynamics, our findings highlight the emergence of carnivory as a process fundamentally determining human evolution.
Full Paper https://doi.org/10.1371/journal.pone.0032452
As far as I know humans developed bigger brains as they ditched foraging plants and hunting animals in favor of agriculture. Systematically growing and breeding our food gave our species a higher and more stable supply of calories. And as brains consume a lot of energy, having enough calories was a prerequisite. Whether these calories and nutrients come from meat or plants doesn’t really matter.
https://phys.org/news/2011-06-farming-blame-size-brains.html
To the best of my knowledge human brain size has decreased about 11% since the advent of agriculture
Brain mass accounted for a substantially larger amount of variance in time to weaning than did body mass
Analysis showed that carnivores systematically wean earlier than omnivores and herbivores. As omnivores and herbivores did not differ with regard to weaning time, they were subsequently pooled in a ‘non-carnivore’ group.
support to the hypothesis that carnivory may be a fundamental determinant of the early human weaning.
Our findings indicate that dietary profile has had a profound evolutionary effect on weaning in mammals and that, if carnivory is taken into consideration, time to weaning is quantitatively predictable with remarkable precision in humans, despite our unique developmental features such as ‘secondary altriciality’
Suggesting that the timing of weaning reflects the developmental needs of the offspring rather than the metabolic limitations of the female.