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Geodakyan's evolutionary theory of sex

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Geodakyan evolutionary theory of sex (ETS) was proposed by Vigen Geodakyan in 1960–80s. This theory has many components related to systemic effects in sex ratios, shapes of phenotypic distributions in male and female phenotypes, sexual dimorphism, mutation rates in genotypes, sex differences in birth ratios, mortality rates, and in susceptibility to new diseases.[1][2][3][4][5][6] Geodakyan started working on the theory in 1965.[7] Two main hypotheses of this theory that complement each other are: the principle of conjugated subsystems and the theory of asynchronous evolution. These hypotheses relate to the paradox of sexual reproduction[8] and suggest an explanation of why sexual reproduction became the most common way of reproduction among three types of reproduction known in biology: asexual, hermaphrodite reproduction and sexual reproduction. The paradox of sexual reproduction (discussed more on the page evolution of sexual reproduction) notes that hermaphrodite reproduction gives the highest diversity of configurations and an easier mating process than bi-sexual reproduction (such as in humans, when half of the members (males) can’t reproduce and can only diversify the genes). Since in bi-sexual reproduction members of species can mate only with the opposite sex, there are fewer opportunities for mating and a lower diversity of outcome of their gene recombinations, in comparison to hermaphrodites. Meanwhile bisexual species still have to share food and other resources with members who don’t reproduce (males). In spite of these disadvantages of bi-sexual reproduction, paradoxically, most plants and animals shifted from hermaphroditism and gonochorism to sexual dimorphism. Why? (Figure 1). (for comparison of types of reproduction see the review:[9] In 2001, Vladimir Iskrin began refining and expanding on Geodakyan's theory.[10]

File:ETS-3reproduc.jpg
Figure 1. Comparison of three types of reproduction: hermaphroditism did not expand in evolution even though apparently it yells a higher diversity of phenotypes

In order to explain this paradox, the ETS has two main hypotheses that complement each other: the principle of conjugated subsystems and the theory of asynchronous evolution.

The principle of conjugated subsystems[edit]

The first hypothesis analyses the sex differences of the shapes of phenotypic distributions. Since Darwin it has been noticed that within one species, and among related species, males often differ from each other to a higher degree than females,[11][12] creating a wider distribution of phenotypes. In other words, male phenotypes are more different from each other, and female phenotypes are more alike. A wider distribution of male phenotypes (high male variability) means an overrepresentation of males at the extremes of the phenotypic distribution, i.e. that there are more males on both tails of the distribution (for example with respect to intelligence, more mentally challenged and more geniuses) than females. In terms of heights, males show more extremes than women among the tallest and the shortest people on Earth. Such differences have been especially discussed in relation to human intelligence (see Variability hypothesis) but Geodakyan was focused on other sex differences in plants and animals The phenomenon of greater male variability was found in primates and humans with respect to physical characteristics[12][13] intelligence,[14][15][16] personality traits,[17] temperament traits,[18] in semantic perception,[19] physical aggression[20] and other psychological characteristics.[21] This phenomenon coincides with the common understanding that male sex (i.e. sex differentiation) emerged and was used by species in mostly variable environments.[22][23] Computer simulations indeed showed that variability and unpredictable behaviour by a part of a group optimize results for the whole group.[24]

Geodakyan suggested that sex dimorphism gives a species the benefit of having two functional partitions, or subsystems. The male sex is considered an operative, variation subsystem, while the female sex is a conservative one. Sex differentiation allows a species to use the male partition to try out various genetic changes, including parasitic and cooperative co-existence for possible inter-species co-evolution and expansion of ecological niches. In Geodakyan's terms, species use males as an experimental partition of sex and use another partition (female) to maintain the features of the species that were proven to be beneficial.[1][2][3][4][25][26][27]

Geodakyan suggested that several mechanisms were developed during different stages of sex evolution to provide this specialization. Compared to females, males have a higher birth rate but also higher mortality, experience more mutations, inherit fewer properties of their parents, have narrower reaction norm (Figure 2), higher aggressiveness, riskier behavior and other properties that can expand ecological niches of their species.[28]

File:ETS-distribution2.jpg
Figure 2. . Shapes of distribution of phenotypes and functional roles of two sex partitions of species. (A): Evolutionary Theory of Sex points out to the evolutionary value of the bisexual system (males expand and females conserve the beneficial characteristics of their species), reflected in sex differences in the shape of distribution (B) and sex-specific behaviour

.

Theory of asynchronous evolution[edit]

The second hypothesis, the theory of asynchronous evolution, describes a phylogenetic "distance" between the sexes. According to this hypothesis, genetic changes appear asynchronously in the two sexes. At the initial, divergent phase, evolutionary changes in a trait emerge primarily in males, as in a testing partition of the species. In subsequent generations the trait evolves in both sexes.[5][29][30][31][32][33][34][35][36][37][38][39][40] A similar theory was described later by other authors.[41]

The hypothesis was published in more than 150 scientific publications (mostly in Russian), covering different aspects of sex related questions—longevity, differentiation of brain and hands, sex chromosomes, mechanisms of sex ratio regulation, heart diseases and other illnesses. The theory was included in the textbooks,[42][43] college study programs,[44][45] was covered in newspaper and magazine articles[46][47][48] and TV programs.[49][50][51]

Predictions and observations[edit]

In the 1965–85 Geodakian conducted an analysis of sex ratios, of dispersion patterns, sex dimorphism in different mutation levels, phenotypic and genotypic diversity of two sexes, feedback control of sex ratios, rates of birth, rates of mortality, and, susceptibility to new diseases.[1][2][3][4] In 1973 he predicted a wider reaction norm of females, as a "conservative" partition that secures beneficial features of a species.[52][53][54] About twenty anthropological characteristics of humans for which the data on both sexual dimorphism and ontogenetic dynamics were obtained were analysed in perspective of the ETS, such as relative length of legs, forearm, fingers, head index, tooth arch, epicanthus, aquiline nose, erythrocyte concentration in the blood, pulse frequency, brain asymmetry, norm and time of reaction, olfaction, and perception of bitter taste of phenylthiourea. This data was in line with the predictions of the ETS.[55][56]

Moreover, if the hypothesis is valid, the differences between monozygotic female twins must be greater than between male monozygotic twins. At the same time in dizygotic twins like in common siblings, the opposite must be true. This can be explained as following: diversity of phenotypes is composed from a genotype-related variance (that in turn, includes (1) reaction norm (i.e. typical features of species, such as humans having two legs and two arms) plus (2) genetic deviations from this norm) and (3) environment-related variance. Geodakyan suggested that males differ from females by having a wider genetic deviations (i.e. (2) component) whereas females have a wider (1) component reaction norm and are more sensitive to environmental adjustment (component (3)):

  • M [===(1)===] [=====(2)=====] [==(3)==]
  • F [=====(1)=====] [==2==] [====3====]

In monozygotic twins the impact of genotypes (i.e. factors (1) and (2) is much stronger than in dizygotic twins. A higher (stronger) contribution of a genetic component (2) in males and a stronger contribution of the component (3) in females, hypothesized by Geodakyan, are expected to emerge as a higher similarity in male monozygotic twins but weaker similarity (higher diversity) in dizygotic male twins, in comparison to females.

Rusalov (1993) in his analysis of sex differences in temperament[57] found that females scored significantly higher on temperament scales measuring verbal-social endurance and tempo and males scores higher on physical endurance and tempo scales. Rusalov suggested that the verbal superiority of females is in line with Geodakyan's view about the function of the female partition of a species as designed to synchronize the norms and values of the community. Trofimova[58][59] reviewed the most consistent psychological and behavioural sex differences and linked them to the Geodakyan's (ETS). She suggested a pattern of consistent sex differences in physical, verbal and social dis/abilities is in line with the ETS’ idea about functional differentiation of a species into conservational, and variational partitions. In females, superiority in verbal abilities, rule obedience, socialisation, empathy and agreeableness was presented as a reflection of the systemic conservation function of the female sex. Male superiority in risk- and sensation seeking, physical abilities, higher rates in physical aggression, psychopathy, dyslexia, autism, schizophrenia, higher birth and accidental death rates was a reflection of the systemic variational function (testing the boundaries of beneficial characteristics) of the male sex. As a result, psychological sex differences might be influenced by a global tendency within a species to expand its norm of reaction, but at the same time to preserve the beneficial properties of the species.

Criticism and upgrade[edit]

Gavrilov and Gavrilova, in their analysis of sex differences in longevity reviewed Geodakyan's ETS.[60] They pointed out that even though females indeed live, in average, longer than males, when it comes to extreme cases of longevity, it is males, and not females who represent the majority of people with exceptionally long lives. They recommended to investigate further molecular-genetic mechanisms of (statistically speaking) longer life in females. Over-representation of males among the oldest centenarians is in line with the interpretation of the male variability phenomenon by the ETS: males have wider distribution of longevity than females, and therefore the extreme cases should be represented by males more than by females.

Trofimova[58] suggested a "redundancy pruning" hypothesis as an upgrade of ETS theory. She pointed out that the variational function of the "male partition" might also provide irrelevance/redundancy pruning of an excess in a bank of beneficial characteristics of a species, in spite of resistance from the norm-driven conservational partition of species. This might explain contradictory sex differences, allocating a high drive for social status/power in the sex with the least abilities for social interaction. The higher the rates of communicative disorders and psychopathy in males, the easier it is for them to disengage from normative expectations and to act under social disapproval.

Comparison with other theories[edit]

  • As noted by Trofimova,[58] the ETS coincides with the theories suggesting that the emergence of sex assisted the fight against pathogens (see Red Queen hypothesis).

References[edit]

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  2. 2.0 2.1 2.2 Geodakyan, V. A. (1987). "Sexual Dimorphism is a Consequence of any Selection". Towards a New Synthesis in Evolutionary Biology. Proc. Intern. Symp. Praha. Czech. Acad. Sci. pp. 168–170. Search this book on Amazon.com Logo.png
  3. 3.0 3.1 3.2 Geodakyan, V. A. (1991). "The Evolutionary Theory of Sex". Priroda. 8: 60–69.
  4. 4.0 4.1 4.2 Geodakyan, V. A. (1996). "Sex Chromosomes: What Are They For? (A New Concept)". Dokladi RAN. 346 (4): 565–569.
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