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Direct reciprocity was proposed by Robert Trivers as a mechanism for the evolution of cooperation. [1] If there are repeated encounters between the same two players in an evolutionary game in which each of them can choose either to "cooperate" or "defect", then a strategy of mutual cooperation may be favoured even if it pays each player, in the short term, to defect when the other cooperates.
Therefore, parents allot equal investment of effort in both sexes. More generally, the expected sex ratio is the ratio of the allotted investment between the sexes, and is sometimes referred to as Fisherian sex ratios. However, there are many examples of organisms that do not demonstrate the expected 1:1 ratio or the equivalent investment ratio.
The McDonald–Kreitman test [1] is a statistical test often used by evolutionary and population biologists to detect and measure the amount of adaptive evolution within a species by determining whether adaptive evolution has occurred, and the proportion of substitutions that resulted from positive selection (also known as directional selection).
The tertiary sex ratio is equivalent to the adult sex ratio (ASR), which is defined as the ratio of adult males to females in a population. [ 6 ] [ 7 ] The operational sex ratio (OSR) is the ratio of sexually active males to females in a population, and is therefore derived from a subset of the individuals included when calculating the ASR. [ 7 ]
Fisher's principle is an evolutionary model that explains why the sex ratio of most species that produce offspring through sexual reproduction is approximately 1:1 between males and females. A. W. F. Edwards has remarked that it is "probably the most celebrated argument in evolutionary biology". [1]
The Trivers–Willard hypothesis has been applied to resource differences among individuals in a society as well as to resource differences among societies.Investigations in humans pose a number of practical and methodological difficulties, [6] but while a 2007 review of previous research found that empirical evidence for the hypothesis was mixed, the author noted that it received greater ...
In biology, the idea of an unbeatable strategy was proposed by W.D. Hamilton in his 1967 paper on sex ratios in Science. [1] [2] In this paper Hamilton discusses sex ratios as strategies in a game, and cites Verner as using this language in his 1965 paper [3] which "claims to show that, given factors causing fluctuations of the population's primary sex ratio, a 1:1 sex-ratio production proves ...
These are direct phenotypic benefits, sensory bias, the Fisherian runaway hypothesis, indicator traits and genetic compatibility. In the majority of systems where mate choice exists, one sex tends to be competitive with their same-sex members [ 4 ] and the other sex is choosy (meaning they are selective when it comes to picking individuals to ...