Mate choice

[1] These mechanisms are a part of evolutionary change because they operate in a way that causes the qualities that are desired in a mate to be more frequently passed on to each generation over time.

These are direct phenotypic benefits, sensory bias, the Fisherian runaway hypothesis, indicator traits and genetic compatibility.

He was perplexed by the elaborate ornamentation that males of some species have, because such features appeared to be detrimental to survival and to have negative consequences for reproductive success.

There he described a scenario, Fisherian runaway, where feedback between mate preference and a trait results in elaborate characters such as the long tail of the male peacock.

This became known as Bateman's principle, and although this was a major finding that added to the work of Darwin and Fisher, it was overlooked until George C. Williams emphasised its importance in the 1960s and 1970s.

[15] The act of being choosy was likely selected for as a way to assess whether or not a potential partner's contribution(s) would be capable of producing and/or maintaining the viability of an offspring.

Utilizing these behaviors usually results in two types of benefits to the individual who is being choosy: Usually, animal biologists assume that mate choice is biased against relatives because of the negative consequences of inbreeding.

[19][20] One example of a sexually selected trait with direct benefits is the bright plumage of the northern cardinal, a common backyard bird in the eastern United States.

[22] The sensory-bias hypothesis states that the preference for a trait evolves in a non-mating context and is then exploited by the less choosy sex in order to obtain more mating opportunities.

In a study done on great reed warblers, models based on the polygyny threshold and sexy-son hypotheses predict that females should gain evolutionary advantage in either short-term or long-term in this mating system.

Such a process shows how female choice could give rise to exaggerated sexual traits through Fisherian runaway selection.

Traits perceived as attractive must reliably indicate broad genetic quality in order for selection to favor them and for preference to evolve.

This is an example of indirect genetic benefits received by the choosy sex, because mating with such individuals will result in high-quality offspring.

[36] The good genes hypothesis states that the choosy sex will mate with individuals who possess traits that signify overall genetic quality.

[37] To test this hypothesis, red jungle-fowl males were infected with a parasitic roundworm and monitored for growth and developmental changes.

The researchers found that parasites affected the development and final appearance of ornamental traits and that females preferred males who were not infected.

[38] One of many examples of indicator traits is the condition-dependent patch of red feathers around the face and shoulders of the male house finch.

In a much-cited manipulation experiment, female house finches were shown to prefer males with brighter red patches.

MHC genes code for receptors that identify foreign pathogens in the body so that the immune system may respond and destroy them.

[42] Mates that have MHC genes different from one another will be superior when reproducing with regard to parasite resistance, body condition and reproductive success and survival.

[50] In species where mating biases exist, females are typically the choosy sex because they provide a greater parental investment than males.

[59] Mate choice behaviours are thought to be important forces that can result in speciation events because the strength of selection for attractive traits is often very strong.

Speciation by this method occurs when a preference for some sexual trait shifts and produces a pre-zygotic barrier (preventing fertilisation).

In a mate choice study, female guppies were shown to prefer males with colour patterns that are typical of their home stream.

A barrier to gene flow exists from South to North as a result of the female choice, which can eventually lead to speciation.

According to Bateman's principle, human females display less variance in their Lifespan Reproductive Success, due to their high obligatory parental investment.

[68] This could gain them resources; provide genetic benefit, as through the sexy son hypothesis; facilitate a desired break-up; and allow them to assess a mate's suitability as a long-term partner.

[71] For a long-term relationship, males may look for commitment, facial symmetry, femininity, physical beauty, waist–hip ratio, large breasts,[72] and youth.

[87][88] Human leukocyte antigen (HLA) proteins are essential for immune system functioning and are highly variable, assumed to be a result of frequency-dependent parasite-driven selection and mate choice.

[101] Recently, researchers have started to ask to what extent individuals assess the cognitive abilities of the opposite sex when choosing a mate.