Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

The degree of expression of secondary sexual traits in mammals is determined by the level of sex hormones. This varies in dependence on various external factors. These factors also include the psychological condition of the individual and this state is closely connected in a number of species with the success or lack of success in various social interactions occurring within the group to which the individual belongs. Interactions can be considered to correspond both to direct physical combat and other forms of competition between individuals, as well as various forms of indirect competition, during which the individuals do not interact physically, but nonetheless measure their success or failure through comparison with the other individuals in the population. It has been demonstrated in a great many species of fauna, including humans, that the testosterone level increases with success and decreases with failure. Simultaneously, the individual need not personally directly participate in the success. For example, it has been found that the level of testosterone increased in the fans of a winning football team by an average of 28%, while that in fans of the defeated team decreased by 27% (Holden 1995).

            If a particular individual wins repeatedly, either in physical combat with his opponents, in advancement in employment, in working success or in success with women, or if he is simply often on the winning side, he will frequently exhibit an elevated testosterone level. In time, this will be manifested in an increased level of expression of secondary sexual traits. Thus an increased level of expression of secondary sexual traits can act as a measure of the success of the particular individual and can thus be used by members of opposite sex as an indicator of the fitness of the sexual partner.s