Persistence of polymorphism in a population as a function of Ne generations. Average of 500 simulations. Simulations were run until one allele was lost due to genetic drift. Numbers on lines indicate model numbers

Persistence of polymorphism in a population as a function of Ne generations. Average of 500 simulations. Simulations were run until one allele was lost due to genetic drift. Numbers on lines indicate model numbers

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Homosexuality has been documented throughout history and is found in almost all human cultures. Twin studies suggest that homosexuality is to some extent heritable. However, from an evolutionary perspective, this poses a problem: Male homosexuals tend to have on average five times fewer children than heterosexual males, so how can a phenomenon asso...

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... Fourth, a few studies have found that in traditional societies, females with MTF siblings have higher fertility (e.g., Iemmola and Ciani, 2009;Vanderlaan et al., 2011), or receive other fitness-enhancing benefits (Vasey et al., 2007). Theoretical modelling suggests that such an effect could maintain the genes required for a non-reproductive caste of MTF over time (e.g., Chaladze, 2016). However, because of their apparent increasing frequency in modern 4. Anthropological and Evolutionary Demography societies (Leinung and Joseph 2020), important future life history research should also examine the role and possibly adaptive nature of FTM individuals in human cooperative breeding kin groups. ...
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Human evolutionary demography is an emerging field blending natural science with social science. This edited volume provides a much-needed, interdisciplinary introduction to the field and highlights cutting-edge research for interested readers and researchers in demography, the evolutionary behavioural sciences, biology, and related disciplines. By bridging the boundaries between social and biological sciences, the volume stresses the importance of a unified understanding of both in order to grasp past and current demographic patterns. Demographic traits, and traits related to demographic outcomes, including fertility and mortality rates, marriage, parental care, menopause, and cooperative behavior are subject to evolutionary processes. Bringing an understanding of evolution into demography therefore incorporates valuable insights into this field; just as knowledge of demography is key to understanding evolutionary processes. By asking questions about old patterns from a new perspective, the volume—composed of contributions from established and early-career academics—demonstrates that a combination of social science research and evolutionary theory offers holistic understandings and approaches that benefit both fields. Human Evolutionary Demography introduces an emerging field in an accessible style. It is suitable for graduate courses in demography, as well as upper-level undergraduates. Its range of research is sure to be of interest to academics working on demographic topics (anthropologists, sociologists, demographers), natural scientists working on evolutionary processes, and disciplines which cross-cut natural and social science, such as evolutionary psychology, human behavioral ecology, cultural evolution, and evolutionary medicine. As an accessible introduction, it should interest readers whether or not they are currently familiar with human evolutionary demography.
... The persistence of gay genes in human population represents an evolutionary puzzle due to obvious reproductive disadvantage. It is possible that being a carrier of gay genes provides some reproductive benefits (Chaladze, 2016), but the exact nature of these benefits remains to be established. ...
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The presence of homosexual behavior in the human population represents an evolutionary puzzle, as such behavior leads to obvious reproductive disadvantages. Recently, it was revealed that the length of telomeres inherited by offspring is determined, among other things, by the age of father. Older fathers pass longer telomeres to their children. The length of telomeres is generally considered as one of the factors determining the individual life span, which suggests that children of older fathers live longer. This phenomenon may provide a plausible explanation for the persistence of homosexuality among humans. Homosexuality is a partially inheritable trait. As homosexual males do not actively pursue reproductive sex, they are much likelier to become fathers later in life, if they reproduce at all. Through delayed reproduction, homosexual and bisexual subpopulations contribute to the increasing mean length of telomeres in population, which results in the gradually increasing life span. However, longer telomeres inherited from homosexual father are passed together with the genes predisposing to homosexual behavior, which helps to sustain a substantial pool of “gay genes” despite their reproductive disadvantage. The described effects are likely to be small but may results in a significant demographical shifts (increased longevity and sustained presence of homosexual sub-population) over multiple generations. The introduction of effective contraception (and the consequent serious increase of the mean age of fathering the children) may provide a similar mechanism for extending the mean telomere length in population, with consequences for longevity and general health.
... Na základě výsledků výše uvedených studií lze říci, že přímá genetická evidence pro lokalizaci genetické komponenty mužské sexuální orientace na chromosomu X tedy zůstává sporná. Chaladze (2016) konstatuje, že některé dosud rozporné výsledky při prokazování genetického podkladu homosexuality mohou plynout z faktu, že do heterosexuální skupiny byli zařazeni muži s genetickou predisposicí k homosexualitě, u nichž se ovšem tato predisposice neprojevila. ...
... Novější výzkumy jednovaječných dvojčat, která jsou geneticky identická, ukazují, že pravděpodobnost, se kterou bude sourozenec se svým dvojčetem sdílet neheterosexuální orientaci, je okolo 20 % (Bailey et al., 2000;Langstrom et al., 2010). Na tento nedostatek předchozích modelů odpovídá Chaladze (2016). Podle něj by i jednolokusový model mohl být stabilní, pokud by nositel homosexuální alely měl jen 20% či 50% pravděpodobnost rozvinutí homosexuality. ...
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Regarding the fact that gay men leave less offspring than straight men, it is appropriate to raise a question by which means is male homosexuality maintained in a population and what could eventually be its evolutionary role. The aim of this paper is to summarize theories that try to explain male homosexuality within the framework of evolution. Furthermore, it aims to critically evaluate the results of empirical research that support particular theories or give evidence against them. In the first part, the paper provides a review of knowledge about the genetic and immunological origins of male homosexuality which consequently serves as a theoretical base for the main part of the paper that pursues the five most influential evolutionary theories of male homosexuality.
... It is thus suggested that greater fecundity and fertility of female relatives of homosexual men can explain the persistence of a nonadaptive form of male sexuality through sexually antagonistic selection (e.g., Ciani and Pellizzari 2012;Zietsch et al. 2008). In other words, sexually antagonistic genes can bring advantages for one sex (e.g., higher fecundity in women) but can be principally disadvantageous for the other sex (e.g., can cause exclusive homosexuality in men).However, as shown by recent models, the frequency of only female carriers cannot explain a stable proportion of exclusive male homosexuals in the population but a large proportion of both nonhomosexual female and male carriers can (Chaladze 2016). Based on behavioral genetic studies, a considerable proportion of men carrying the homosexual genes are not exclusively or predominantly homosexual. ...
... Similarly, in India, many nonheterosexual individuals live in forced marriages to avoid social stigma and bear children biologically (Gwalani 2015;Jain, 2015). Being homosexual doesn't mean that the individual cannot reproduce; however, male homosexuals tend to have five times fewer children compared to male heterosexuals on average (Chaladze, 2016). ...
... A study involving individual-based modeling (IBM), which used population genetics models, showed that male homosexuality can be maintained in a low to stable frequency in a population if "roughly more than half of the females and half of the males" are carriers of genes that predispose a male to be homosexual (Chaladze, 2016). A major question that arises here is whether such carrier males and females exist in a population. ...
... Even if the degree of altruism required to offset reproductive benefits is rarely or never realized in the human population, the 33% increase in fecundity of ascending females on the maternal side of gay and bisexual men, relative to heterosexuals, might be able to offset the direct benefits of reproduction and hence not selected against by natural selection (Camperio-Ciani et al., 2004Iemmola & Camperio ciani, 2008). Simulation models proposed by Chaladze (2016) that explain such propagation by male and female carriers further supports this observation. ...
Article
Since the 20th century, multiple studies have linked the variations in human sexual orientation, from heterosexuality to bisexuality or homosexuality, to a wide range of biological factors. However, a clear mechanism that leads to the development of these variations has not been established yet. This review consolidates various comprehensive studies on the possible biological factors in the fields of genetics, epigenetics, uterine environment, hormones , neuroanatomy, and neurobiology that lead to these variations. One intriguing question that 'homosexuality phenotype' faces is its ability to avoid elimination by Darwinian selection. This review tries to explain why natural selection is not eliminating the genetic factors associated with homosexuality even at the cost of the evolutionary fitness of homosexual individuals. Studies supporting certain strong candidates for alternative sexual orientation (ASO) are highlighted, which can become new research avenues for investigators in this field. Further, a novel speculation is proposed that might be contributing to the development of variation in human sexuality.
... It is thus suggested that greater fecundity and fertility of female relatives of homosexual men can explain the persistence of a nonadaptive form of male sexuality through sexually antagonistic selection (e.g., Ciani and Pellizzari 2012;Zietsch et al. 2008). In other words, sexually antagonistic genes can bring advantages for one sex (e.g., higher fecundity in women) but can be principally disadvantageous for the other sex (e.g., can cause exclusive homosexuality in men).However, as shown by recent models, the frequency of only female carriers cannot explain a stable proportion of exclusive male homosexuals in the population but a large proportion of both nonhomosexual female and male carriers can (Chaladze 2016). Based on behavioral genetic studies, a considerable proportion of men carrying the homosexual genes are not exclusively or predominantly homosexual. ...
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Este livro foi pensado para ser um primeiro texto introdutório às bases ecológicas e evolutivas do comportamento humano, voltado para o ensino ao nível de graduação. Embora cada capítulo possa ser lido em qualquer ordem, organizamos de modo que a sequência sugerida permita ao aprofundamento paulatino dos diferentes conceitos e disciplinas dedi- cadas aos estudos do comportamento humano.