Impact of Carnivory on Human Development and Evolution Revealed by a New Unifying Model of Weaning in Mammals

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

Men’s oppressive beliefs predict their breast size preferences in women

Previous studies of men’s breast size preferences have yielded equivocal findings, with studies variously indicating a preference for small, medium, or large breasts. Here, we examined the impact of men’s oppressive beliefs in shaping their female breast size ideals. British White men from the community in London, England (N = 361) viewed figures of women that rotated in 360° and varied in breast size along five levels. They then rated the figure that they found most physically attractive and also completed measures assessing their sexist attitudes and tendency to objectify women. Results showed that medium breasts were rated most frequent as attractive (32.7 %), followed by large (24.4 %) and very large (19.1 %) breasts. Further analyses showed that men’s preferences for larger female breasts were significantly associated with a greater tendency to be benevolently sexist, to objectify women, and to be hostile towards women. These results were discussed in relation to feminist theories, which postulate that beauty ideals and practices in contemporary societies serve to maintain the domination of one sex over the other

Natural parenting : back to basics in infant care

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