Sexual Selection in Human Evolution - Basics

Basics

Charles Darwin described sexual selection as depending "on the advantage which certain individuals have over others of the same sex and species, solely in respect of reproduction". In animals, he saw the competition for advantage as occurring between males - the most successful of which were chosen by females. However, in humans, Darwin came to think the evidence pointed toward male choice; he believed sexual selection could explain otherwise puzzling features of the human species, including some aspects of appearance which vary geographically but seem to be trivial and superficial, such as beards.

Geoffrey Miller, drawing on some of Darwin's largely neglected ideas about human behavior, has hypothesized that many human behaviors not clearly tied to survival benefits, such as humor, music, visual art, verbal creativity, and some forms of altruism, are courtship adaptations that have been favored through sexual selection. In that view, many human artefacts could be considered subject to sexual selection as part of the extended phenotype, for instance clothing that enhances sexually selected traits.

Some hypotheses about the evolution of the human brain argue that it is a sexually selected trait, as it would not confer enough fitness in itself relative to its high maintenance costs (a quarter to a fifth of the energy and oxygen consumed by a human). Related to this is vocabulary, where humans, on average, know far more words than are necessary for communication. Miller (2000) has proposed that this apparent redundancy is due to individuals using vocabulary to demonstrate their intelligence, and consequently their "fitness", to potential mates. This has been tested experimentally, and it appears that males do make greater use of lower-frequency (more unusual) words when in a romantic mindset compared to a non-romantic mindset, meaning that vocabulary is likely to be used as a sexual display (Rosenberg & Tunney, 2008).

The evolutionary biologist Richard Dawkins has speculated that the loss of the penis bone in humans, when it is present in other primates, may be due to sexual selection by females looking for a clear sign of good health in prospective mates. Since a human erection relies on a hydraulic pumping system, erection failure is a sensitive early warning of certain kinds of physical and mental ill health.

However, sexual selection's role in human evolution cannot be definitively established, as features may result from an equilibrium among competing selective pressures, some involving sexual selection, others natural selection, and some may be accidental and due to pleiotropy.

The German anthropologist Ferdinand Fellmann has proposed a modified form of sexual selection, termed "emotional selection,“ as the pivot in human emotional evolution. The survival edge is due to the talent of humans for long-term mating, which allows to have feelings about feelings: the origin of human consciousness.