Females who choose their mates carefully are less likely to lose their reproductive investment. Males can be subject to strong selection for specific traits favored by females. Most women consider these traits an indicator of their partner's fitness. Selection in favor of females who choose males increases their offspring's chances of success. Males with more elaborate or colorful decorations may indicate a mate's worth and may have a chance to mate with a particular female.
While mating is essential, it can be a costly event - females should be pickier about mates than males because mating risks, such as aggression or transmission, can affect adverse effects on the reproductive performance of offspring. Female selection theory asserts that most human females, like the females of many other mammals, have developed mating preferences in favor of males adept at providing resources.
The four major evolutionary models of women's mate selection are the 'direct utility,' 'good genes,' 'transient selection,' and 'sensory bias' models.
In the direct utility model, selection favors genetically predisposed females to choose mates with tangible resources, such as protection from predators.
In systems where the offspring do not benefit directly, selection may favor females who choose mates possessing so-called "good genes." Evolutionary biologists have theorized that traits that are accurate and honest indicators of male genetic quality should be used by females when choosing between males based on genes.
In a model of pervasive sexual selection, there is a genetic correlation between a male trait and a female preference for that trait. For example, if the frequency of one increases, says, by the selection, the other will also increase because of this correlation. This process can "snowball," resulting in dramatic masculine features and solid feminine preferences.
In the affective bias model of mate selection, females initially prefer a trait in males because the female's nervous system reacts to that trait outside of the context of mate selection life.
Two main mechanisms to explain offspring mate selection have been proposed: good genes and the arbitrary Fisherian process.
In the "good gene" scenario, differences between males provide females with information about the genetic qualities of different males that females may inherit. In the "good genes" model, as in the "direct interest" models, there is a correspondence between the supposed role of natural selection versus sexual selection since the preference for particular offspring in certain males may allow females to achieve higher survivability and fertility.
For example, Good genes can be those that allow a male to carry a "defect" while surviving despite a troublesome trait, genes that signal disease resistance, or genes that are more compatible with the offspring's genes. Evidence for offspring selection for good genes remains sparse despite decades of research on female mate selection in many species. This apparent lack of success continues to spark debate about the importance of good genomic modeling in this area.
Named after R. A. Fisher, who originally proposed this model, it suggests that women's preferences may evolve for arbitrary traits and does not provide information on male qualities and therefore does not reinforce the effects of natural selection. If the female develops a preference for a particular trait, the male carrying that trait will be selected as a mate.
This mixed mating will establish a genetic correlation between preference and trait. The fitting advantage of the arbitrary trait exists only because of its covariance with preferences. By selecting a male with a particular trait value, the female obtains the indirect benefit of producing offspring that will be more sexually attractive to females of that preference.
This process can lead to an uncontrollable positive feedback loop in which the trait becomes more exaggerated as preference selection increases. However, other models have shown that feedback loops such as so are just one of many possible evolutionary outcomes of the Fisherian process.
Women's answers to personal advertisements in newspapers by males are one piece of evidence. If women's tastes influenced their mating decisions, they should respond more frequently to males who suggest they are financially secure. Baize and Schroeder (1995) used a sample of 120 personal advertisements from two newspapers, one from the West Coast and one from the Midwest, to test this assumption. The authors issued a questionnaire to persons who placed the ads, inquiring about their situation, response rate, and personality traits.
Many characteristics predicted the number of letters men got in response to their advertisements. Secondly, age was a significant predictor, with women reacting to older males more frequently than younger ones. Second, income and education were significant predictors, with women responding to advertising showing better wages and more years of education than males. A study of response rates to ads made by 551 males in Poland revealed similar findings. Guys with greater levels of education, males who were slightly older, taller, and offered more resources all received more responses from women than men who lacked these attributes.
A second set of results is on women who can obtain what they want, women who have the attributes men want in a spouse, such as physical beauty. What are these women's partner preferences? Researchers observed in three sociological studies that physically beautiful women married men with better social standing and financial assets than less attractive women. One study linked women's physical beauty to their spouses' vocational status.
The correlations for different groups were all positive, ranging from +0.23 to +0.37. The Institute of Human Development in Berkeley, California, did longitudinal research. Staff members rated the physical attractiveness of then-unmarried women while they were teens. This group of women was followed up on in adulthood after marriage, and their husbands' employment statuses were examined.
Working-class and middle-class women's outcomes were analyzed separately. About a decade later, the associations between a woman's beauty in adolescence and her husband's occupational level were +0.46 for working-class women and +0.35 for middle-class women. In the sample, a woman's physical beauty is linked more strongly with her husband's position (+0.43) than other women's factors, such as social class. In conclusion, beauty in women appears to be an essential avenue to upward mobility; women who are best able to acquire what they want to appear to choose men with the attributes most women desire—men with prestige and riches.
Demographic information on the age disparities between brides and grooms at marriage provides a third data source on women's real partner choices. Remember that women exhibit a preference for older males. In a worldwide survey of thirty-seven countries, women preferred males who were 3.42 years older on average.
Twenty-seven of these countries provided demographic data on real age disparities. The actual age difference between brides and grooms in this group was 2.99 years. Grooms were older on average than brides in every country, ranging from 2.17 years in Ireland to 4.92 years in Greece. In summary, women's desire for older husbands results in marriages to older males. Women's actual mating decisions are consistent with their declared preferences.
Substantial anti-incest prejudice is associated with first-degree relatives in primates, including humans. Both non-human great apes and humans avoid relationships with first-degree relatives (i.e., parent-child or sibling). Avoiding incest is an evolutionary mechanism to prevent unwanted alleles and phenotypes from persisting in a population. There are many mechanisms to avoid incest, both social and biological, including gender-based dispersion.
Although incest avoidance is common among humans and non-human primates, only humans have social consequences for incestuous behavior. In most Western societies, there are clear and strict laws against incest between first kin (parents and children and between siblings. In non-human primates, an essential mechanism for avoiding incest is sex-based dispersion.
Most social groups of primates consist of several reproductive females and one to several males. In most groups, males or Breeding females leave their breeding group. In primates, infants and adolescents have a long development period; Parenting familiarity indicates genetic association. Therefore, the offspring and children or siblings are not fertile.
Mating with close relatives often reduces reproductive success (inbreeding failure) because it increases the risk that rare, dangerous recessive alleles will be expressed in the progeny. However, incest can occur when animals do not have adequate knowledge of kinship or when the cost to avoid inbreeding is too high. Father-son mating was completely avoided. The avoidance of incest is evident in genetic and social mate selection. Paternity analysis using microsatellites revealed that birds are almost always limited in choosing close relatives as genetic partners.
The theory of mate selection predicts that animals have developed strategies to mate with genetically dissimilar partners optimally, conferring a fitness advantage. When adults do not disperse in group species, the assessment of kinship among species can be a critical factor in mate selection. Binary selection tests show that females prefer to mate with non-sibling males over sibling males, thus avoiding incest.
In addition, inbreeding significantly reduces their chances of successful reproduction. Contrary to what might be expected when females choose between a non-sibling member of the herd and a non-breeding member, they do not avoid mating with distant non-breeding members. , and extreme inbreeding increased their reproductive success.
The four major evolutionary models of women's mate selection are the direct utility, good genes, transient selection, and sensory bias models. Good genes can be those that allow a male to carry a "defect" while surviving despite a troublesome trait, genes that signal disease resistance, or genes that are more compatible with the offspring's genes.
Fisher's Arbitrary Choice suggests that women's preferences may evolve for arbitrary traits, leading to an uncontrollable positive feedback loop in which the trait becomes more exaggerated as preference selection increases.
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