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= Mate Choice = Mate choice, also known as intersexual selection, is an evolutionary process in which selection is dependent on the attractiveness of an individual’s phenotypic traits. Evolutionary change is possible because the qualities that are desired in a mate are more frequently passed on to each generation over time. For example, if female peacocks desire mates who have a colourful plumage, then this trait will increase in frequency over time as male peacocks with a colourful plumage will have more reproductive success.

Mate choice is one of two components of sexual selection, the other being intrasexual selection. Ideas on sexual selection were first introduced in 1871, by Charles Darwin, then expanded on by Ronald Fisher in 1915. At present, there are five mechanisms that explain how mate choice has evolved over time. These are direct phenotypic benefits, sensory bias, the Fisherian Runaway hypothesis, indicator traits and genetic compatibility.

In systems where mate choice exists, one sex is competitive with same-sex members and the other sex is choosy (this means they are selective when it comes to picking individuals to mate with). There are direct and indirect benefits of being the selective individual. In most species, females are the choosy sex that discriminate amongst competitive males, but there are several examples of reversed roles (see below). It is preferable for an individual to choose a compatible mate of the same species, in order to maintain reproductive success.

Mate Choice in Human Males
Generally, it is unusual for males within a species to be the choosy sex. In humans, when sexual reproduction takes place, a male's sperm fertilizes an egg cell of a female. Following this, the female is obliged to endure a nine month pregnancy and childbirth. This means that females naturally provide a greater parental investment to offspring, than males. Human males have a larger quantity of gametes than females, which provides them with a greater window of opportunity to mate and reproduce. A male's sperm is replenished at a rate of approximately 12 million per hour, whereas a female is born with a fixed amount of egg cells which are not restocked.

However, males can be influenced by certain traits of females when choosing a mate:

Short-Term Mating Strategies
When finding a short-term mate, males highly value women with sexual experience and physical attractiveness. Men assume that women who have engaged in sexual experiences beforehand are likely to have a higher sex drive than women who haven't. Also, research has shown that men who are interested in a short-term sexual relationship are more likely to prioritise information about the body of potential partners, rather than their faces.

Long-Term Mating Strategies
Although from a evolutionary perspective women are usually the choosy sex, humans have the ability to rely on biological signals of reproductive success, such as a waist-to-hip ratio of 0.7, and non-biological signals such as the female's willingness to marry. Unlike many animals, humans are not able to change colour when they are ready to mate, for example, so they have to verbally and physically communicate with the opposite sex.
 * Commitment and marriage: A human male may be interested in mating with a female who seeks marriage. This is because he has exclusive sexual access to the female, so any offspring produced in the relationship will to be genetically related to him (unless the female as sexual intercourse with another male outside of the marriage). With two married parents investing in the offspring, their chance of survival may increase; therefore the male's DNA will be passed on to the children of his offspring. Also, a male who is interested in committing to a female may be more attractive to potential mates. A male who can promise resources and future parental investment is likely to be more appealing to women than a male who is unwilling to commit to her.
 * Facial maturity: Faces that appear younger are usually rated as more attractive by males. This could include faces which do not have many wrinkles or where there is very clear skin. A female who appears younger is likely to be appealing to mates, as it suggests that she has a higher reproductive value than alternative, older, females.
 * Waist-to-hip ratio of the potential female mate: A waist-to-hip ratio of 0.7 is an indicator of fertility, lower long-term health risks and suggests that the woman isn't already pregnant. A male is likely to desire these qualities in a mate, as it will increase the chance of survival of any offspring the couple have together.