Sexual dimorphism in size

Almost all human population groups show sexual dimorphism in stature where females are significantly shorter than males.  Some exceptions do occur in populations living under stressful conditions where this sexual dimorphism is diminished. Very often the reason given for this situation is the impact of malnutrition which affects the females relatively less than the males thus reducing the dimorphism. Sexual dimorphism in size is present not only in humans but in living primates such as chimpanzee and gorilla also. Traditional explanation offered for this size dimorphism among primates was the fights among males of a group for the possession of the females which ultimately led to sexual selection of larger males. Social behavior of primates indicates that the strongest male among monkeys becomes the alpha who controls the females of the group and all other males also submit to him. Did this situation of sexual selection due to fights among males prevailed in primitive human societies to control women? The answer may be in negative, as the primitive human societies survived due to mutual cooperation and not because of the rivalry. In fact natural selection would also favour larger females as this would give them advantage in child birth where survival chances of the mother child would increase. Researchers Touraille and Gouyon published a new hypothesis of sexual dimorphism in size in Nature Precedings in 2008. According to this hypothesis, it may be the cost (mainly of food) rather than the evolutionary advantage which led to sexual dimorphism in size.

If women have to be larger, the cost incurred on them would be greater. Hierarchical structure of primitive societies had shown a clear dominance of males who would get the best quality of food over the females. This differential food allocation seems to have played a significant role in maintaining sexual dimorphism in size. Therefore cultural evolution coupled with natural selection was responsible for maintaining the sexual dimorphism.