Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by “selective responses by animals to particular stimuli” that can be viewed as behavior.  In other words, before an animal mates with a potential mate, they first evaluate various aspects of that mate that are indicators of quality – such as the resources they have or the phenotype – and evaluate whether they are characteristic or not. Somehow beneficial to them. Any kind of feedback will be there after evaluation.
These mechanisms are part of evolutionary change because they work in such a way that desired traits in a mate are passed on more frequently to each generation over time. For example, if female peacocks want to mate with colored feathers , the frequency of this trait will increase over time as male peacocks with colored feathers will have greater reproductive success .  Further investigation of this concept found that it is actually the distinctive blue and green colors near the eyes that increase females’ chances of mating with a specific peacock. 
Mate choice is one of two components of sexual selection , the other being intrasexual selection. Ideas on sexual selection were first introduced by Charles Darwin in 1871, then expanded by Ronald Fisher in 1915. Currently, there are five sub mechanisms that explain how mate choice has evolved over time. These are direct phenotypic advantage, sensory bias, the Fisherian runaway hypothesis, indicative traits and genetic compatibility.
In most systems where mate choice exists, one sex is competitive with its same-sex members  and the other is gender selective (meaning that individuals are selective when they choose to mate. are there). There are direct and indirect benefits to being a selective individual. In most species, the female is the selective sex that discriminates between competing males,  but there are many examples of reversed roles (see below). It is better for an individual to select a compatible mate of the same species in order to maintain reproductive success.  Other factors that may influence mate choice include pathogen stress andThe major histocompatibility complex (MHC) is involved.
Origin and History
Charles Darwin first expressed his views on sexual selection and mate choice in his 1871 book The Descent of Man, and Selection in Relation to Sex . He was surprised by the elaborate ornamentation of males of some species, as such features appeared to be detrimental to survival and have negative consequences for reproductive success. Darwin proposed two explanations for the existence of such traits: these traits are useful in male-male warfare or they are preferred by females.  This article focuses on the latter. Darwin considered natural selection and sexual selection as two separate disciplines, although in the 1930s biologists defined sexual selection as a part of natural selection. 
In 1915, Ronald Fisher wrote a paper on female preference and the development of secondary sexual characteristics .  Fifteen years later, he expanded this theory in his book The Genetic Theory of Natural Selection . There he described a scenario where the reaction between mate preference and a trait results in elaborate characters such as the long tail of male peacocks (see Fisherian runaway ).
In 1948, using Drosophila as a model, Angus John Bateman presented experimental evidence that male reproductive success is limited by the number of mates, while female reproductive success is limited by the number of pregnancies that can occur in her lifetime. Is.  Thus a female must be selective when choosing a mate as the quality of her offspring depends on it. Males must fight for mating opportunity, in the form of intra-sexual competition, as not all males will be selected by females. This is known as Bateman’s theory , and although it was a major discovery that combined the work of Darwin and Fischer, it was ignored until George C. Williams.did not emphasize its importance in the 1960s and 1970s.
In 1972, shortly after Williams’ revival of the subject, Robert L. Trivers presented his parental investment theory. Trivers defines parental investment as any investment made by a parent that benefits its present child at the cost of investment in future offspring. These investments include the cost of producing gametes as well as other care or effort provided by the parents after birth or hatching. Correcting Bateman’s views, Trivers argued that the sex that displayed low parental investment (not necessarily male) would have to compete for mating opportunities with the more investing sex. Differences in parental investment levels create a situation that favors mating biases.
direct and indirect benefits
The act of being selective was chosen as a way of assessing whether the contribution of a potential partner would be capable of producing and/or maintaining the viability of the offspring. Using these behaviors typically provides two types of benefits to the person who is selective:
- Direct benefits increase the fitness of the selected sex through direct physical gains or resources. These benefits include, but are not limited to, increased territory quality, increased parental care, and protection from predators. There is much support for the maintenance of mate choice by direct benefit  and this approach provides the least controversial model to explain discriminatory mating. 
- Indirect benefits increase genetic fitness for the offspring, and thus increase the inclusive fitness of the parents. When it appears that the selective sex does not receive a direct benefit from its mate, an indirect advantage may pay off for being selective. These indirect advantages may include having higher quality genes for their offspring (known as adaptive indirect advantages) or genes that make their offspring more attractive (known as arbitrary indirect advantages).
As of 2018 five proposed mechanisms address the evolution of mate choice:
- direct phenotypic advantage
- sensory bias
- runaway fisherman
- indicative symptoms
- genetic compatibility
Direct and/or indirect benefits drive the mating biases described in each mechanism. It is possible that these mechanisms co-occur, although the relative roles of each have not been adequately evaluated.
direct phenotypic advantage
A select mate has preferences for certain types of traits—also called phenotypes—that will make them an advantage in potential mates. These traits must be reliable, and must be commutative of something that directly benefits the chosen partner in some way.  Prioritizing intercourse in this situation is beneficial as it directly affects fertility. The direct benefits are widespread and empirical studies provide evidence for this mechanism of development.  
An example of a sexually selected trait with a direct advantage is the bright plumage of the northern cardinal, a common backyard bird in the eastern United States. Male northern cardinals have distinctive red plumage, while females have a more cryptic coloration. In this example, females are the selective sex and males will use feather brightness as a signal when choosing a mate – research shows that males with bright plumage feed their young more often than males with dull plumage .  This helps to take care of the children and takes some of the burden off the mother so that she can produce more children without any help.
Although this particular mechanism operates on the premise that all phenotypes must communicate something that directly benefits the chosen mate, such selected phenotypes may also have additional indirect benefits for the mother by benefiting the offspring. For example, with increasing aid in feeding their young with more feather-glow as seen in northern cardinals, the total amount of food given to the offspring increases – even if the mother has more babies.  Although females may choose this trait with the direct advantageous purpose of allowing more time and energy to be allocated to producing more offspring, it also benefits the offspring as there are two parents instead of one. provide food, which likely increases the total amount of food available to the offspring, despite a potential increase in the amount of offspring siblings.
The sensory-bias hypothesis states that a preference for a trait develops in a non-mating context and is then exploited by the less selective sex to obtain more mating opportunities. Competitive sex develops traits that take advantage of the pre-existing bias that the selective sex already possesses. This tantra is thought [ by whom? ] because it produces a divergence of signaling systems which are carried over reproductive isolation to explain notable trait differences in closely related species. 
Sensory bias has been demonstrated in guppies, freshwater fish from Trinidad and Tobago. In this mating system, female guppies prefer to mate with males with a more orange body-colour. However, outside one mating context, both sexes consciously prefer orange objects, which suggests that the preference originally evolved in another context, such as foraging.  It is rare that orange fruits fall in streams where guppies live. The ability to quickly locate these fruits is an adaptive trait that has developed outside of a mating context. Shortly after the attachment to orange objects was born, male guppies took advantage of this preference by adding large orange spots to attract females.
Another example of sensory exploitation is the case of the water mite Neumania papillator , an ambush predator that preys on copepods (small crustaceans) passing into the water column.  While hunting, N. The papillator adopts a distinctive stance called the “net stance”: it holds its first four legs in the water column, with its four hind legs resting on aquatic vegetation; This allows it to detect vibrational stimuli generated by swimming prey and to use it to orient and capture prey.  During courtship, males actively seek out females;  If a male finds a female, he slowly circles around the female while his first and second legs tremble near her.  Females (who were in a “pure stance”) are oriented toward the male and often hold onto the male, causing the male’s feet to tremble.  It does not harm the male or prevent further courtship; The male then deposits the spermatozoa and begins to fan vigorously and flick his fourth pair of legs over the spermatozoa, generating a stream of water that travels up the sperms and toward the female.  Sometimes the sperm-packet is lifted by the female.  Heather Proctor hypothesized that the vibrations of the male legs mimic those detected by the female swimming prey. This would trigger female prey-detection responses, causing the females to orient and then hold onto the males, mediating prey.  If this was true and males were exploiting female predator responses, then hungry females should be more receptive to male tremors. Proctor found that unfed captive females tend to orient and clutch at males than do captive females that are fed, consistent with the sensory exploitation hypothesis. 
Other examples of sensory-bias mechanisms include traits in oxtails,  wolf spiders,  and mankins.  More experimental work is needed to reach a full understanding of the prevalence and mechanisms of sensory bias. 
fisherman runaway and sexy-son hypothesis
This creates a positive feedback loop in which a particular trait is desired by a female and is present in a male, and the desire and presence of that particular trait is reflected in their offspring.  If this mechanism is strong enough, it can lead to a type of self-reinforcing co-evolution.  If runaway selection is strong enough, it may incur significant costs, such as increased visibility for predators and the energetic cost to maintain full expression of the trait. Hence the peacock’s extraordinary plumage, or any number of leks, displays mating. This model does not predict genetic advantage; Rather, the reward is more companionship.
In a study on great reed warblers, models based on the polygyny threshold and the Sexy-Son hypothesis predict that females should have an evolutionary advantage in this mating system, either in the short-term or long-term. Although the importance of female choice was demonstrated, the study did not support the hypothesis. [ citation needed ] Other studies, such as those on long-tailed widowbirds, have demonstrated the existence of female choice. [ citation needed ]Here, females chose males with longer tails, and even preferred males whose tails were experimentally longer than shorter tails and naturally occurring lengths. Such a process would suggest how female choice through Fischerian runaway selection can lead to exaggerated sexual traits.
Indicative traits indicate a good overall quality of life. Traits considered attractive must reliably indicate broad genetic quality for selection in their favor and for preference to evolve. This is an example of indirect genetic advantages obtained by selective sex, as mating with such individuals will result in higher quality offspring. The indicator trait hypothesis is divided into three highly related subthemes: the constraint theory of sexual selection, the good gene hypothesis, and the Hamilton–Zuck hypothesis.
People rate the importance of certain traits differently when referring to themselves or others as ideal long-term partners. Research shows that women consider traits indicating genetic fitness to be more important to their mate, while preferring traits that provide an advantage to others over their sister’s ideal mate. 
Indicative symptoms are situation-dependent and have associated costs. Therefore, individuals who can handle these costs well ( cf. “I can do X [here, I can survive] with a hand behind my back”) are desired by the selector sex for their superior genetic traits. should be. This is known as the constraint theory of sexual selection . 
The good gene hypothesis states that the finicky sex will mate with individuals who possess traits that indicate overall genetic quality. In doing so, they gain an evolutionary advantage for their offspring through indirect advantage.
The Hamilton-Zuk hypothesis holds that sexual ornaments are indicators of parasite- and disease-resistance.  To test this hypothesis, red jungle-chicken males were infected with a parasitic roundworm and monitored for growth and developmental changes. Female preference was also assessed. The researchers found that the parasite influenced the development and final appearance of ornamental traits and that females preferred males who were not infected. This supports the idea that parasites are an important factor in sexual selection and mate choice. 
One of the many examples of suggestive traits is the position-dependent patches of red feathers around the face and shoulders of the male house finch. This patch varies in brightness between individuals because the pigments that produce the red color (carotenoids) are confined in the environment. Thus, males that have a high quality diet will have bright red plumage. In a manipulation experiment, female house finches were shown to prefer males with bright red patches. In addition, males with naturally bright patches proved to be better fathers and exhibited higher offspring-feeding rates than dull males.  This study is cited heavily in the literature and provides solid support for the indicator-symptom hypothesis that there is a direct benefit.
Genetic compatibility refers to how well the genes of two parents work together in their offspring. Choosing a genetically compatible mate allows the offspring to be better fit and may notably affect reproductive fitness. However, the genetic compatibility model is limited to specific traits due to complex genetic interactions (for example the major histocompatibility complex in humans and mice). In order to select a suitable mate the select sex must know its own genotype as well as the genotype of potential mates.  This makes testing components of genetic compatibility difficult and controversial.
Role of the major histocompatibility complex
A controversial but well-known experiment shows that human females use body odor as an indicator of genetic compatibility. In this study, men were given a plain T-shirt to sleep on for two nights to provide a sample of the smell. The college women were then asked to rate the smell from several men, some with similar MHC (Major Histocompatibility Complex) genes and others with different genes. The MHC gene codes for receptors that identify foreign pathogens in the body so that the immune system can respond and destroy them. Since each different gene in the MHC codes for a different type of receptor, It is therefore expected that females would benefit from mating with males who have more divergent MHC genes. This will ensure better resistance to parasites and disease in the offspring. The researchers found that females had higher rates of smell if the male’s genes differed more from their own. They concluded that odors are influenced by the MHC and have consequences for mate choice in the human population today.
Similar to humans in the odor-rating experiment, animals also choose mates based on genetic compatibility, as determined by evaluating the body odor of their potential mate(s). Some animals, such as rats, assess a mate’s genetic compatibility based on their urine odor. 
In an experiment studying three-spined sticklebacks, researchers found that females preferred to mate with males that share a greater diversity of the major histocompatibility complex (MHC) and in addition to fighting the common parasite Gyrodactylus salaris . They also have specific MHC haplotypes.  Partners that have different MHC genes from each other will be better off when breeding with regards to parasite resistance, body condition, and reproductive success and survival. 
Animal genetic diversity and life reproductive success (LRS) at the MHC level are optimal at intermediate levels rather than at their maximum,   despite MHC being one of the most polymorphic genes.  In one study, researchers found that mice heterozygous at all MHC loci were less resistant to Salmonella than mice homozygous at all loci, therefore displaying many different MHC alleles due to increased loss of T-cells was disadvantageous.  that aid an organism’s immune system and trigger its appropriate response. 
MHC diversity may also correlate with MHC gene expression. As long as a genetic component is present in the expression pattern, natural selection is able to act on the trait. Therefore, gene expression for MHC genes may contribute to the natural selection processes of some species and may indeed be evolutionarily relevant. For example, in another study of the three-spined stickleback, exposure to a parasitic species increased MHC class IIB expression by more than 25%, proving that parasitic infection increases gene expression. 
MHC diversity in vertebrates can also be generated by recombination of alleles on the MHC gene. 
sex role reversal in animals
In species where mating biases exist, females are generally the sex selective because they provide greater parental investment than males. However, there are some instances of sex role reversal where females must compete with each other for mating opportunities with males. Species that exhibit parental care after the birth of their offspring have the ability to overcome gender differences in parental investment (the amount of energy that each parent contributes per offspring) and Leads to a reversal of sexual roles.  The following are examples of male mate choice (sex role reversal) in many taxa.
- Fish: Male fish generally display a high degree of parental care (see pipefish, scissortail sergeant, and seahorses). This is because females deposit their eggs in a special brooding pouch that is held by the male. She does not participate in parental care after this incident. The male then has the burden of raising the offspring on his own which requires energy and time. Thus, males in these species must choose from among competing females for mating opportunities. Surveys of several species of pipefish suggest that gender differences in the level of parental care may not be the only reason for the reversal. The mating system (EI monogamy and polygamy) can also significantly affect the appearance of male mate choice. 
- Amphibians: Male poison-arrow frogs ( Dendrobates auratus ) play a very active parenting role. Males attract females to breeding sites where they deposit their eggs. The male fertilizes these eggs and accepts the burden of protecting and caring for them until they become independent. Since the male contributes a higher level of parental investment, females must compete for opportunities to release their eggs with the limited available males. 
- Birds: Bird species are usually biphasic in care, and can also be maternal, like the Guyanese cock-of-the-rock. However the reverse may also be true. Male jacans provide all parental care after the female has laid the eggs. This means that the male incubates the eggs and guards the nest for a long time. Because males put a lot of time and energy into the offspring, females are very competitive for the right to lay their eggs in an established nest. 
- Mammals: There are no confirmed cases of the sex role of the inverted mammal, but the female spotted hyena has a peculiar anatomy and behavior that has received a lot of attention.  Female spotted hyenas are much more aggressive than males due to higher levels of androgens during development. Increased male hormones during development contribute to an increased pseudopenis that is involved in mating and birth.  Although anatomical and behavioral roles differ from accepted norms, spotted hyenas do not perform sex role reversal because females do not compete with each other for mates. 
For many years it has been suggested that sexual isolation caused by differences in mating behavior is a precursor to reproductive isolation (lack of gene flow), and consequently species in nature.  The behavior of mate choice is regarded as important forces that can result in speciation events because the forces of selection for attractive traits are often very strong. Specificity by this method occurs when the preference for certain sexual traits is altered and creates a pre-zygotic barrier (preventing fertilization). With recent advances in genetic modeling these processes have become difficult to test.  Species by sexual selection are gaining popularity in the literature with an increase in theoretical and empirical studies.
There is evidence of early speciation through mate preference in guppies. Guppies are located in several different streams in Trinidad and male color patterns vary geographically. Female guppies have no color scheme, but their preferences for these color patterns also vary from place to place. In a mate choice study, female guppies were shown to prefer males with color patterns that are specific to their domestic stream.  This preference can result in reproductive isolation if the two populations come into contact again. There is a similar trend shown in two species of wood white butterfly, L. reali and L. mustard. female L. sinapisIt controls mate choice by engaging in specific mating only, while males attempt to mate with any species. The choice of this female mate has encouraged the speculation of the two wood gourds. 
The black-throated blue songbird, a North American bird, is another example. Asymmetric recognition of local and non-local songs has been found among two populations of black-throated blue warriors in the United States, one in the northern United States (New Hampshire) and the other in the southern United States (North Carolina). Males in northern populations respond strongly to local male songs but relatively weakly to non-local songs of southern males. In contrast, Southern men react equally to both local and non-local songs. The fact that northern males exhibit differential identity indicates that northern females do not mate with “heterosexual” males from the south; Thus it is not necessary for the northern men to vigorously respond to the song of the southern challenger. Female choice results in a disruption of gene flow from south to north, which may eventually lead to speciation.
mate selection in humans
In humans, males and females differ in their strategies for obtaining mates and focusing on certain traits. There are two main categories of strategies that are used by both genders: short-term and long-term. Human mate choice depends on a variety of factors, such as ecology, demographics, access to resources, rank/social status, genes and parasitic stress.
While some common mating systems are observed in humans, the amount of variation in mating strategies is relatively large. This is because of how humans evolved over a wide variety of geographically and ecologically diverse regions. This diversity, as well as cultural practices and human consciousness, have all led to a large amount of variation in mating systems. Below are some broad trends in female partner choice.
female partner choice
However, in humans, both males and females are selective in who they decide to mate with, as seen in nature, females tend to choose a greater mate choice than males. However, relative to most other animals, female and male mating strategies are found to be more similar to each other than to be distinct. According to Bateman’s theory of lifespan reproductive success (LRS), human females exhibit the least variance of the two sexes in their LRS due to their high compulsive parental investment, which is a gestational period of nine months, with Also breastfeeding after birth is in order. To feed the offspring so that their brain can grow to the required size. 
Human female sexual selection can be examined by looking at the ways in which males and females are sexually dimorphic, in particular traits that serve some other evolutionary purpose. For example, male traits such as the presence of a beard, overall low voice pitch, and average high height are considered sexually selected traits because they provide an advantage either to the females who select for them or to their offspring. Huh. Experimentally, women have reported a preference for men with beards and low voices.  
Female mate choice hinges on several different matching male traits, and trade-offs between many of these traits need to be assessed. However, the most important traits for female human mate choice are parental investment, resource provision, and the provision of good genes to the offspring. Many phenotypic traits are chosen because they serve as an indication of one of these three dominant traits. The relative importance of these traits when considering mate selection varies depending on the type of mating arrangement females have. Human females typically employ long-term mating strategies when selecting a mate, although they also engage in short-term mating arrangements, so their mate choice preferences vary depending on the type of arrangement being performed. 
short term mating strategies
Females do not always seek and engage in long-term mating arrangements. This is evidenced by factors such as an evolved male propensity to seek multiple sexual partners—a trait that could not have developed if females had not historically been involved in short-term arrangements  —and by the tendency of some females to follow. Tendency to do affairs outside of their long-term pairings.
David simply outlines several hypotheses as a function of women’s short-term mate choices:
- Resource Hypothesis: Females may engage in short-term mating to obtain resources that they may not be able to obtain from a long-term partner, or a long-term partner may not be able to provide consistently. These resources may be food, protection for the female and her children from aggressive males who may seize or sexually coerce them, or to obtain status by granting the female high social status. Females may also benefit from multiple short-term mating arrangements through paternity illusion – if the paternity of her offspring is not certain, she may be able to accrue resources from multiple males as a result of this uncertainty. 
- Genetic advantage hypothesis: Females are likely to engage in short-term mating arrangements if their long-term partner is infertile, to obtain better genes for their long-term mates, to aid in conception, or to obtain different genes for those option can be selected. Increase in the genetic diversity of her mate and her offspring. This is related to what is known as the sexy son hypothesis; If a female inherits genes from a higher quality male, her offspring will likely have higher mate value, resulting in increased reproductive success. 
- Mate Removal and Mate Switching: Females may engage their long-term partner in a short-term mating arrangement to end their relationship; In other words, to facilitate the break-up. Women can also use short-term mating if their current partner has depreciated in value, and they want to ‘trade-up’ and find a mate they believe is of higher value. 
- Short-term to long-term goals: Women may use short-term sexual relations to assess a partner’s value as a long-term partner, or in the hope that a short-term arrangement will result in a long-term . 
long term mating strategies
While there has been evidence and research to support the existence of short-term intercourse in women, it has still been shown that women prefer long-term partners over short-term mates. This preference is due to the investment tendency of women and the need for more energy for parenting. In long-term mating arrangements, females typically seek males who provide a high level of parental investment, and who can provide resources to the female or her offspring. [ citation needed ]The provision of economic resources, or the ability to acquire multiple economic resources, is the most obvious indication of a man’s ability to provide resources, and has been shown experimentally to evaluate their importance to women in the United States. has gone. Partner’s financial status higher than that of men. However, several other traits exist that may serve as an indication of a male’s ability to provide sexually selected resources throughout the evolutionary history of females. These include older age – older men have more time to acquire resources – diligence, dependence and stability – for her and her offspring if a woman’s long-term partner is not emotionally stable or trustworthy The provision of resources is likely to be inconsistent. Additionally, the costs associated with an emotionally unstable partner such as jealousy and manipulation may outweigh the benefits associated with the resources they are able to provide. 
Choosing a female partner is not as straightforward as selecting a partner who displays all her desired qualities. Often, potential mates will have some qualities that are desirable and some that are not, so women must assess the qualities of their potential partners and the relative costs and benefits of the ‘trade-off’. Female mate choices will also be constrained by the context in which they are making them, resulting in conditional mate choices.  Some of the conditions that influence female mate choice include the female’s own perceived attractiveness, the female’s personal resources, mate imitation, and parasitic stress. 
male partner choice
In general, it is unusual for males to be the selective sex within a species. There are many reasons for this. In humans, after sexual reproduction, the female is bound to endure nine months of pregnancy and childbirth.  This means that females naturally provide more paternal investment to offspring than males.   Human males have a greater number of gametes than females, which are replenished at a rate of about 12 million per hour. In contrast, female humans are born with a certain amount of egg cells, which are not shed for a lifetime.  This gives males more opportunities for mating and reproduction than females, so females are generally more selective.
Although not generally gender selective, human males can be influenced by certain traits of females when making decisions about potential mates: 
short term mating strategies
When looking for a short-term mate, men place the utmost importance on women with sexual experience and physical attractiveness.  Men seeking short-term sex are more likely to avoid women who are interested in commitment or require investment.
Examples of short-term mating strategies in men:
- Multiple sexual partners: When looking for short-term sexual relationships, men want as little time between each partner as possible.  When having sex with multiple partners, it is important to know that there may be an increased risk of contracting a sexually transmitted disease if contraception is not used.
- Physical attractiveness: Men who are interested in short-term sexual relationships are more likely to prioritize information about potential partners’ bodies rather than their faces.  When looking for a woman for a short-term relationship compared to a long-term relationship, men are less likely to prioritize factors such as commitment.
- Relaxation of standards: It has been reported that men are more likely to have sex with women who have low levels of intelligence, independence, conscientiousness, generosity, athleticism, responsibility and cooperativeness, when the relationship is short-lived.  Men may generally accept lower standards more than they like, because they are not entering into a long-term relationship with this person.
- Sexual Experience: Many men believe that women who have had sexual experiences before are more likely to have a higher sex drive than women who have not.  These females may also be more accessible and require less courtship.
long term mating strategies
Although females are usually the selective sex from an evolutionary standpoint, if a human male has the desire to reproduce he may look for certain qualities in a potential mate who may be the mother of his offspring. Humans have the ability to rely on biological cues of reproductive success and non-biological cues, such as the female’s readiness to marry.  Unlike many animals, humans are not able to consciously display physiological changes to their bodies when they are ready to mate, so they have to rely on other forms of communication before consensual relationships can occur. .
Males can find:
- Commitment and Marriage: A human male may be interested in having intercourse with a female who wishes to marry.  This is because the female has exclusive sexual access to her, so any offspring born in the relationship will be genetically related to her (unless the female mates with another male outside of marriage). This increases the chances of surety of paternity. The more two married parents invest in the offspring, the greater their chances of survival; Therefore the male’s DNA will be passed on to the children of his offspring. Also, a man who is interested in working with a woman may be more attractive to potential mates. A man who can promise the investment of resources and future parents is likely to be more attractive to women than a man who is not committed to her.
- Facial Symmetry: Symmetrical faces are judged to indicate good general health and a woman’s ability to withstand adverse environmental factors such as illness. 
- Femininity: A feminine face can be a sign of puberty, which in turn indicates a strong reproductive value.  As a woman ages, her facial features become less feminine as she ages. Femininity may also be linked to increased immunity and higher estrogen levels, which are factors that suggest reproductive value to a potential mate.
- Physical beauty: Observable characteristics of a woman may indicate good health and ability to reproduce, qualities that are likely to be desired by a man. This may include smoother skin, absence of sores, increased muscle tone, longer hair and higher energy levels. 
- Resources: Men who are looking for a long-term partner may strive to obtain higher status or resources, such as their own home or job promotion.  This may increase their chances of attracting the mate they want.
- Waist-to-Hip Ratio: A waist-to-hip ratio of 0.7 is an indicator of fertility, low long-term health risk, and indicates that a woman is not already pregnant.  A male is likely to desire these qualities in a mate, as this will increase the chances of any offspring living together.
- Breasts: Men generally prefer women with bigger breasts as it is a sign of age between 20-24 years. A woman in this age group is considered more fertile, sexually mature and reproductively healthy. Large breasts are also an indicator of having a higher body fat percentage, which saves more energy during gestation to provide nutrients to the fetus as well as increase the productivity of breastfeeding. Although breast size is important for male attractiveness because it is so prominent, the areola pigment is also found to be important. As women get older and participate in more pregnancies, their circle becomes darker in pigment. So, Darker areoles look more attractive because they indicate that the woman is capable of successfully giving birth to healthy babies. Although it is considered attractive only in women with large breasts. If a woman’s breasts are small or medium-sized, a lighter areola is preferred by men because it becomes lighter as a woman goes through puberty. As such, she is still viewed as fertile, cannot be considered sexually mature and reproductively healthy as a woman with larger breasts and a darker areola.
- Puberty: Both young and old are attracted to women in their twenties.   Younger-looking faces are generally perceived by men as more attractive.  This may include a clear-skinned face and lack of wrinkles, as well as white eyes and red cheeks and lips.  A woman who appears younger is more likely to be attractive to her mates, as it suggests that she has a higher reproductive value than alternative, older women. As a female celebrates her twentieth birthday, her reproductive value steadily declines until about the age of fifty.
Parasitic stress on mate choice
The parasitic stress theory, otherwise known as pathogen stress, states that parasites or diseases emphasize the development of organisms, leading to a change in the appearance of their sexually attractive traits. In societies with a high prevalence of parasites or pathogens, members of that society derive a greater evolutionary advantage from the selection of physical attractiveness/good looks of their potential mates than members of a society with a low prevalence of parasites or diseases. Less emphasis on physical attractiveness. This indicates that physical attractiveness serves as a method by which humans can determine resistance to parasites, as it is believed that parasites and disease reduce the ability of those people to portray attractive traits. will provide those who are suffering from or are suffering from a disease, and will also limit the number of high quality pathogen resistant cohorts.
The Hamilton–Zuck hypothesis  (see Indicative traits) has greatly influenced research into human mate choice. Preliminary research has shown that, within a species (brightly colored birds), there is greater sexual selection for males that have brighter plumage (feathers). Furthermore, Hamilton and Zuck showed that, among many species, there is greater selection for physical characteristics in species under greater parasitic stress. In cultures where parasitic infection is particularly high, members of that society use the signals available to them to determine the physical health status of a potential mate.  Regardless of wealth or ideology, women from areas of society that are at higher risk or have higher rates of parasites and diseases will regard masculinity as a higher priority.
Hamilton-Zuck hypothesis in humans
- Scarification: In pre-industrial societies, body markings such as tattoos or scarification are predicted to be a way by which an individual can attract potential mates by indicating an individual’s reproductive quality. Meaning, markings on the body may be viewed by potential mates as evidence that an individual has overcome parasites and thus is more attractive to potential mates.  Research examining this hypothesis (Singh and Bronstad 1997) found that in cases of increased pathogens, the only anatomic area with evidence of scarification in females was found on the abdomen, with no evidence for male scarification. . 
- Masculinity: In societies that have high levels of parasites or diseases, women in that society, as the overall health of its members declines, begin to place more emphasis on masculinity over their mates.  Specifically, women look for increased signs of masculinity in areas such as men’s voices, face, and body shape.  The face, in particular, may bear several cues for parasite resistance  and has been the subject of most fascination research. 
- Polygamy: Tropical regions were originally associated with polygamous societies and this was a result of the surrounding environment being ecologically rich and homogeneous.  However, while tropical regions were associated with polygamy, pathogen strain is considered a better indicator of polygamy and is positively correlated with it. In addition, during human evolution, areas that had high levels of parasite-stress shifted the polygamy threshold and increased the presence of certain types of polygamy in society. 
Gangstad & Buss (2009) say that research indicates that parasitic stress affects mate choice only through females searching for “good genes” that show parasite resistance, in areas where The spread of parasites is high.  John Cartwright also points out that females can only protect themselves from parasite transmission rather than selecting males with good genes, and females seek out more than just parasite-resistant genes. 
MHC-correlated mate choice
The major histocompatibility complex (MHC) or, in humans, human leukocyte antigen (HLA) produces proteins that are essential for the functioning of the immune system. The genes of the MHC complex have extremely high variability, which is thought to be the result of frequency-dependent parasite-driven selection and mate choice. It is believed to promote heterozygosity thereby improving the chances of survival of the offspring.
In experiments using rats, mate choice involving the MHC indicated that odor cues played a role.  In humans, there is conflicting evidence about whether men and women will perceive the smell of the opposite sex as more pleasant if the potential mate has an MHC-dissimilar antigen.  Although women on birth control pills perceive the smell of MHC-identical men as more pleasant, it is unknown why women on birth control pills smell this way. It was found that MHC-like odors were processed faster when processed. Contrary to these findings, other studies have found no association between attractiveness and odor by testing men’s odor preferences over women’s odors. The study concludes that dissimilar HLA proteins have no association in attractiveness between men and women.  Research on a southern Brazilian student population resulted in similar findings that found significant differences in men’s sweat and attractiveness ratings given the MHC-difference. 
Human facial preferences have been shown to correlate with both MHC-similarity and MHC-heterozygosity.  Research into MHC-similarity in relation to facial attractiveness is limited, but research so far suggests that women looking to have long-term relationships will choose men who are MHC-like.  While facial asymmetry has not been correlated with MHC-heterozygosity, there appears to be perceived healthyness of the skin.  It appears that only MHC-heterozygosity and no other genetic markers are correlated with facial attractiveness in males  and it has been shown that no correlation has been found in females so far.  Slightly different from facial attractiveness, facial masculinity has not been shown to correlate with MHC asymmetry (a common measure of immunogenicity). 
A review article published in June 2018 concluded that there is no association between HLA and mate choice.  In addition to assessing previous studies to identify errors in their research methods (such as small population sizes) on HLA-mate choice analysis, the study collects a large set of data and revisits the analysis of previous studies. drives. By using large data sets to analyze 30 couples of European descent, they produce findings in contrast to previous studies that identified significant deviations in mate choice according to HLA genotyping. Additional studies have been conducted on African and European populations together showing a correlation of MHC divergence only in European but not African populations. 
Mate Choice for Cognitive Symptoms
In the late 19th century, Charles Darwin proposed that cognition, or “intelligence,” was the product of two combined evolutionary forces: natural selection and sexual selection.  Research on human mate choice has shown that intelligence is sexually selected, and highly regarded by both sexes.   Some evolutionary psychologists have suggested that humans developed larger brains because the cognitive abilities associated with this increase in size were able to attract mates, resulting in increased reproductive success: the brain was able to produce It is metabolically expensive and an honest indication of mate quality. , 
Cognition may function to attract mates by extending beyond humans.  If having higher cognitive skills increases a male’s ability to gather resources, then females may directly benefit from choosing more intelligent males, either through courtship feeding or allofeeding.  Considering that cognitive skills are to some extent hereditary, females may also benefit indirectly through their offspring.  Additionally, cognitive ability has been shown to vary significantly both within and between species, and may result under sexual selection. Recently, researchers have begun to ask the extent to which individuals assess the cognitive abilities of the opposite sex when choosing a mate.  In fruit flies, the absence of sexual selection was accompanied by a decline in male cognitive performance. 
in non-human vertebrates
Female preference for males with increased cognitive ability “may be reflected in successful males’ courtship displays, attractive displays, courtship feeding or diet-dependent morphological traits.”  However, there are few studies that assess whether women can discriminate between men through direct observation of cognitively demanding tasks. Instead, researchers typically examine female choice because of morphological traits related to cognitive ability.
- Budgerigars: Direct observation of problem-solving skills to increase male attractiveness in this species of parrot.  In a two-stage experiment test for female preference, initially less-favorite male budgerigars were preferred when females solved them extractive foraging problems, while initially preferred males failed problem-solving. This shift in preference suggests that women discriminate between men through direct observation of cognitively demanding tasks. 
- Zebra Finches: Researchers conducted a problem-solving experiment similar to the one described above.  However, male problem-solving performance was not found to affect female mating preferences. Instead, females had a significant preference for males with better forging efficiency. There is no evidence that women indirectly assess male cognitive ability through morphological traits. By selecting for males with higher forage capacity, females received a direct feeding advantage. 
- Satin bowerbirds: Bowerbirds are famous for their complex male courtship, in which they use a few colored decorations.  This suggests that male bowerbirds with enhanced cognitive abilities should have a selective advantage during male courtship.  In one study testing problem-solving skills, the general cognitive performance of male satin bowerbirds was found to be related to mating success, making them more sexually attractive.  However, a more recent study evaluated bowerbirds on six cognitive tasks, and found little correlation between them. In a more recent study, bowerbird performance in six cognitive tasks was positively correlated with mating success, but no general cognitive ability was found because the correlations between performance on each task were weak. Instead, mating success can be independently predicted through the male’s performance on most tasks; This demonstrates the complexity of the link between cognitive ability and sexual selection. 
- Red Crossbill: An experimental study has shown that female red crossbills prefer males with higher foraging efficiency.  After watching two males simultaneously remove seeds from the cones, the females spent more time in the proximity of the wild animals more rapidly. Although females may benefit directly and indirectly through their preference for faster foragers, the potential link between foraging efficiency and cognitive abilities was not investigated.  
- Mountain chickadees: In this monogamous bird species, spatial cognition is important because mountain chickadees rely on the retrieval of previously stored food caches to nourish themselves during the winter.  Spatial memory has been shown to be correlated with reproductive success in mountain chicks.  When females mate with males who have increased spatial cognition, they have larger screws and give birth to larger babies, when females have worse spatial cognition than females who mate with females. Therefore, when mating with higher quality males with increased spatial skills, females may attempt to obtain an indirect, genetic advantage by increasing their reproductive investment.
- Guppy: When assessing male cognitive ability through maze experiments, females preferred males who learned the two mazes at a faster rate.  However, women did not directly look at men during their learning tasks. Although females could discriminate between males by assessing orange saturation – a morphological characteristic that is weakly related to learning rate – females did not find males with bright orange spots more attractive. Instead, women may use an unknown visual attribute to discriminate between men and their cognitive abilities. 
- Meadow voles: In this species of rodent, female preference for male spatial ability was examined.  Before females were given a choice between two males, male spatial ability was measured using a series of water maze tests.   Although women did not directly see men completing spatial-ability tasks, they preferred men with advanced spatial skills. This preference may explain why grasshopper brain regions associated with spatial ability are sexually dimorphic: spatial ability may serve as an conscientious indication of male quality because of the metabolic costs associated with brain development.
Although there is some evidence that females assess male cognitive ability when selecting a mate, the effect of cognitive ability on survival and mating preference remains unclear.  A number of questions need to be answered in order to be able to better understand the effect of cognitive traits in mate choice. Some discrepancies also need to be corrected. For example, in 1996, Catchpole suggested that in Songbirds, females preferred males with larger song repertoires. The learned song repertoire was correlated with the size of the High Vocal Center (HVC) in the brain; The women can then use the song repertoire as an indicator of general cognitive ability. However, a recent study found the learned song repertoire to be an unreliable indicator of cognitive ability. Instead of a general cognitive ability, male songbirds were found to have specific cognitive abilities that were not positively associated.
As of 2011, more research was needed into the extent to which cognitive abilities determine success or courtship displays, the extent to which behavioral courtship depends on learning through practice and experience, the extent to which cognitive abilities determine survival and mating. influence success, and which indicator traits can be used as indicators of cognitive ability.  Researchers have begun to explore the relationship between cognition and personality; Certain personality traits such as boldness or neophobia can be used as indicators of cognitive ability, although more evidence is needed to characterize personality-cognition relationships. As of 2011, the empirical evidence for both direct and indirect benefits for choosing mates with enhanced cognition is weak. A possible research direction would be on the indirect benefits of mating with males with enhanced spatial cognition in mountain chicks.   Research on developmental and environmental influences on cognitive ability requires additional attention, as such factors have been shown to influence song learning and may therefore influence other cognitive traits.