Sexual selection in humans
Sexual selection is quite different in non-human animals than humans as they feel more of the evolutionary pressures to reproduce and can easily reject a mate.
Richard Dawkins argued that 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".
"[16] Charles Darwin conjectured that the male beard, as well as the hairlessness of humans compared to nearly all other mammals, were results of sexual selection.
Although not explicit, his observation that in Khoisan women "the posterior part of the body projects in a most wonderful manner" (known as steatopygia)[17] implies sexual selection for this characteristic.
[21] This idea closely relates to that of the suggested need for increased photoprotection and is part of the most-commonly-accepted scientific explanation for the evolution of pigmentary traits.
[24] 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.
[26] It has been suggested the evolution of the human penis towards larger size was the result of female choice rather than sperm competition, which generally favors large testicles.
[29][30] Selection preferences are biologically driven,[31][32] that is, by the display of phenotypic traits that can be both consciously and unconsciously evaluated by the opposite sex to determine the health and fertility of a potential mate.
[34] Some of the factors that affect how females select their potential mates for reproduction include voice pitch, facial shape, muscular appearance, and particularly height;[35][36][37][38] with the possibility of a Fisherian runaway in the making.
[43] Like their female counterparts, males also use visual information about a potential mate, as well as voice, body shape, and an assortment of other factors in selecting a partner.
[44] Furthermore, males also evaluate skin coloration, symmetry, and apparent health, as a means by which they select a partner for reproductive purposes.
[33] Together with visual and chemical signals, these crucial characteristics which are likely to enhance the ability to produce offspring, as well as long-term survival prospects, can be assessed and selections made.
[68][69] Bipedalism is not a common trait, yet many species like the great apes stand on their hind legs when fighting, which increases power behind blows.
[71][72][73][74] Bipedalism and utilizing handheld objects such as weapons may have aided early hominins in contest competition, reducing sexual selection pressures of maintaining large canine teeth.
[49] This may have provided protection against blows to the face during contest competitions as the areas on the skull that have increased robusticity are parts that are more likely to suffer from injury.
[86][87][88][89] Traits that evolve during contest competition, such as large body size and physical aggression, are often costly to produce and maintain.
[91][92][93] Some traits of human males that function in contests, such as body size, strength, and weaponry usage, may also have been selected to aid in hunting.
[97][98] Some behaviors from mothers competing with other females at a similar life stage over resources include self-promotion and competitor derogation.
The indirect aggression in which females engage can take the form of damaging the reputation of other women (e.g., via gossip), potentially influencing their sexual behavior and opportunities.
[107] Greater overall body fat percentage in human females appears to be unique among primates and may function in storing resources needed to gestate and support large-brained offspring[109] as well as in sexual selection.
[110] For example, higher female body mass index (BMI) is associated with increased fertility in young women, particularly those in subsistence societies.
[112] Such traits, particularly body fat distribution, may represent sexual ornamentation, which is important in mating throughout the animal kingdom, for example, in birds.
[113][114] Humans also use bodily decoration, including jewelry, tattoos, scarification, and makeup to enhance appearance and desirability to potential mates.
[116] Facial and vocal attractiveness have been observed to change with estradiol and progesterone in pattens consistent with fertility-related increases,[117] although some data challenge this interpretation.
[119] John Manning[120] suggests that where polygyny is common, there is also a higher disease burden, resulting in selection for antimicrobial resistance.
According to this argument, the anti-infective qualities of melanin were more important than protection from ultraviolet light in the evolution of the darkest skin types.
Manning asserts that skin color is more correlated with the occurrence of polygyny – because melanin has an antimicrobial function – than the latitudinal gradient in intensity of ultraviolet radiation.
[122] Rogers et al. (2004) concluded that dark skin evolved as a result of the loss of body hair among the earliest primate ancestors of humans.
[134] 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.
The first period of brain expansion occurred 2.5 million years ago, when Homo habilis first began using stone tools.
