Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with, and compete with members of the same sex for access to members of the opposite sex. These two forms of selection mean that some individuals have greater reproductive success than others within a population, for example because they are more attractive or prefer more attractive partners to produce offspring. Successful males benefit from frequent mating and monopolizing access to one or more fertile females. Females can maximise the return on the energy they invest in reproduction by selecting and mating with the best males.
Peafowl is a common name for two bird species of the genus Pavo and one species of the closely related genus Afropavo within the tribe Pavonini of the family Phasianidae. Male peafowl are referred to as peacocks, and female peafowl are referred to as peahens.
A lek is an aggregation of male animals gathered to engage in competitive displays and courtship rituals, known as lekking, to entice visiting females which are surveying prospective partners with which to mate. It can also refer to a space used by displaying males to defend their own share of territory for the breeding season. A lekking species is characterised by male displays, strong female mate choice, and the conferring of indirect benefits to males and reduced costs to females. Although most prevalent among birds such as black grouse, lekking is also found in a wide range of vertebrates including some bony fish, amphibians, reptiles, mammals, and arthropods including crustaceans and insects.
Behavioral ecology, also spelled behavioural ecology, is the study of the evolutionary basis for animal behavior due to ecological pressures. Behavioral ecology emerged from ethology after Niko Tinbergen outlined four questions to address when studying animal behaviors: What are the proximate causes, ontogeny, survival value, and phylogeny of a behavior?
The handicap principle is a disputed hypothesis proposed by the Israeli biologist Amotz Zahavi in 1975. It is meant to explain how "signal selection" during mate choice may lead to "honest" or reliable signalling between male and female animals which have an obvious motivation to bluff or deceive each other. The handicap principle suggests that secondary sexual characteristics are costly signals which must be reliable, as they cost the signaller resources that individuals with less of a particular trait could not afford. The handicap principle further proposes that animals of greater biological fitness signal this through handicapping behaviour, or morphology that effectively lowers overall fitness. The central idea is that sexually selected traits function like conspicuous consumption, signalling the ability to afford to squander a resource. Receivers then know that the signal indicates quality, because inferior-quality signallers are unable to produce such wastefully extravagant signals.
Fisherian runaway or runaway selection is a sexual selection mechanism proposed by the mathematical biologist Ronald Fisher in the early 20th century, to account for the evolution of ostentatious male ornamentation by persistent, directional female choice. An example is the colourful and elaborate peacock plumage compared to the relatively subdued peahen plumage; the costly ornaments, notably the bird's extremely long tail, appear to be incompatible with natural selection. Fisherian runaway can be postulated to include sexually dimorphic phenotypic traits such as behavior expressed by a particular sex.
Disassortative mating is a mating pattern in which individuals with dissimilar phenotypes mate with one another more frequently than would be expected under random mating. Disassortative mating reduces the mean genetic similarities within the population and produces a greater number of heterozygotes. The pattern is character specific, but does not affect allele frequencies. This nonrandom mating pattern will result in deviation from the Hardy-Weinberg principle.
Assortative mating is a mating pattern and a form of sexual selection in which individuals with similar phenotypes or genotypes mate with one another more frequently than would be expected under a random mating pattern.
Stalk-eyed flies are insects of the fly family Diopsidae. The family is distinguished from most other flies by most members of the family possessing "eyestalks": projections from the sides of the head with the eyes at the end. Some fly species from other families such as Drosophilidae, Platystomatidae, Richardiidae, and Tephritidae have similar heads, but the unique character of the Diopsidae is that their antennae are located on the stalk, rather than in the middle of the head as in all other flies. Stalked eyes are present in all members of the subfamily Diopsinae, but are absent in the Centrioncinae, which retain unstalked eyes similar to those of other flies. The stalked eyes are usually sexually dimorphic, with eyestalks present but shorter in females.
Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior. In other words, before an animal engages with a potential mate, they first evaluate various aspects of that mate which are indicative of quality—such as the resources or phenotypes they have—and evaluate whether or not those particular trait(s) are somehow beneficial to them. The evaluation will then incur a response of some sort.
The sexy son hypothesis in evolutionary biology and sexual selection, proposed by Patrick J. Weatherhead and Raleigh J. Robertson of Queen's University in Kingston, Ontario in 1979, states that a female's ideal mate choice among potential mates is one whose genes will produce males with the best chance of reproductive success. This implies that other benefits the father can offer the mother or offspring are less relevant than they may appear, including his capacity as a parental caregiver, territory and any nuptial gifts. Fisher's principle means that the sex ratio is always near 1:1 between males and females, yet what matters most are her "sexy sons'" future breeding successes, more likely if they have a promiscuous father, in creating large numbers of offspring carrying copies of her genes. This sexual selection hypothesis has been researched in species such as the European pied flycatcher.
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), vocalizations, mechanical sound production, or displays of beauty, strength, or agonistic ability.
The antagonistic pleiotropy hypothesis was first proposed in a 1952 paper on the evolutionary theory of ageing by Peter Medawar and developed further in a landmark paper by George C. Williams in 1957. Their original hypotheses have since spurred a huge and fruitful literature on the evolutionary explanation for senescence. Pleiotropy is the phenomenon where a single gene influences more than one phenotypic trait in an organism. It is one of the most commonly observed attributes of genes. A gene is considered to exhibit antagonistic pleiotropy if it controls more than one phenotypic trait, where at least one of these traits is beneficial to the organism's fitness and at least one is detrimental to fitness.
Competitive altruism is a possible mechanism for the persistence of cooperative behaviors, specifically those that are performed unconditionally. The theory of reciprocal altruism can be used to explain behaviors that are performed by a donor who receives some sort of benefit in the future. When no such compensation is received, however, reciprocity fails to explain altruistic behavior.
A biological ornament is a characteristic of an animal that appears to serve a decorative function rather than a utilitarian function. Many are secondary sexual characteristics, and others appear on young birds during the period when they are dependent on being fed by their parents. Ornaments are used in displays to attract mates, which may lead to the evolutionary process known as sexual selection. An animal may shake, lengthen, or spread out its ornament in order to get the attention of the opposite sex, which will in turn choose the most attractive one with which to mate. Ornaments are most often observed in males, and choosing an extravagantly ornamented male benefits females as the genes that produce the ornament will be passed on to her offspring, increasing their own reproductive fitness. As Ronald Fisher noted, the male offspring will inherit the ornament while the female offspring will inherit the preference for said ornament, which can lead to a positive feedback loop known as a Fisherian runaway. These structures serve as cues to animal sexual behaviour, that is, they are sensory signals that affect mating responses. Therefore, ornamental traits are often selected by mate choice.
Major histocompatibility complex (MHC) genes code for cell surface proteins that facilitate an organism's immune response to pathogens as well as its ability to avoid attacking its own cells. These genes have maintained an unusually high level of allelic diversity throughout time and throughout different populations. This means that for each MHC gene, many alleles consistently exist within the population, and many individuals are heterozygous at MHC loci.
Genic capture is a hypothesis explaining the maintenance of genetic variance in traits under sexual selection. A classic problem in sexual selection is the fixation of alleles that are beneficial under strong selection, thereby eliminating the benefits of mate choice. Genic capture resolves this paradox by suggesting that additive genetic variance of sexually selected traits reflects the genetic variance in total condition. A deleterious mutation anywhere in the genome will adversely affect condition, and thereby adversely affect a condition-dependent sexually selected trait. Genic capture therefore resolves the lek paradox by proposing that recurrent deleterious mutation maintains additive genetic variance in fitness by incorporating the entire mutation load of an individual. Thus any condition-dependent trait "captures" the overall genetic variance in condition. Rowe and Houle argued that genic capture ensures that good genes will become a central feature of the evolution of any sexually selected trait.
Sexual selection in birds concerns how birds have evolved a variety of mating behaviors, with the peacock tail being perhaps the most famous example of sexual selection and the Fisherian runaway. Commonly occurring sexual dimorphisms such as size and color differences are energetically costly attributes that signal competitive breeding situations. Many types of avian sexual selection have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signaling adaptations ensure that sexually selected ornaments such as plumage coloration and courtship behavior are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviors.
Parasite-stress theory, or pathogen-stress theory, is a theory of human evolution proposing that parasites and diseases encountered by a species shape the development of species' values and qualities, proposed by researchers Corey Fincher and Randy Thornhill.
In humans, males and females differ in their strategies to acquire mates and focus on certain qualities. There are two main categories of strategies that both sexes utilize: short-term and long-term. Human mate choice, an aspect of sexual selection in humans, depends on a variety of factors, such as ecology, demography, access to resources, rank/social standing, genes, and parasite stress.
