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The Trivers–Willard hypothesis sex ratio or investment?

Trivers hypothesisDec 26, 2017. Download citation The Trivers–Willard. The Trivers–Willard hypothesis has commonly been considered to predict two things. First, that a mother in good condition should bias the sex ratio of her offspring towards males if males exhibit greater variation in reproductive value. Second, tha. Explains that the Trivers-Willard hypothesis says that high-status parents favor sons over daughters while low-status parents favor daughters over sons. Examines whether the Trivers-Willard hypothesis is warranted by testing whether its predictions hold true among parents of adolescents in the United States. Finds little evidence to support the Trivers-Willard hypothesis. Next


Trivers–Willard hypothesis - Wikipedia

Trivers hypothesisThe Trivers–Willard hypothesis has been applied to resource differences among individuals in a society as well as to resource differences among societies. Empirical evidence is mixed with higher support in better studies This hypothesis has produced considerable debate within evolutionary biology. Here we use meta-analysis techniques to evaluate claims that nonhuman primate females facultatively adjust the sex ratio of their progeny in relation to their own dominance rank in a uniform way. The magnitude of the difference in birth sex ratios of high- and low-ranking females declines as sample sizes increase, and the mean difference in birth sex ratios of high- and low-ranking females is zero. These results suggest that the observed effects could be the product of stochastic variation in small samples. These findings indicate that presently we cannot reject the null hypothesis that maternal dominance rank is unrelated to birth sex ratios. Next


Conditions for the Trivers-Willard hypothesis to be valid A. - arXiv

Trivers hypothesisThe very insightful Trivers-Willard hypothesis, proposed in the early 1970s, states that females in good physiological conditions are more likely to produce male offspring, when the variance of reproductive success amongst males is high. The hypothesis has inspired a number of studies over the last three decades aimed at. Can shed light on cultural behavior, including the behaviors of composing and telling stories. Where Darwinists interested in literary narrative might differ, however, is in the definition of what should be included in the category of literary narrative:, i.e., does literary narrative refer only to the fine arts or are stories told in tribal societies also examples of literary narrative? Another place where such Darwinists differ is in their view of the function of literary narrative. Those who focus on literature as fine art argue that literary narrative has a cognitive function. 22), as one example, argues that literary narrative satisfies a need, namely a desire for cognitive order. Sugiyama, for example, has argued that by substituting verbal representations for potentially costly first-hand experience, narrative enables an individual to safely and efficiently acquire information pertinent to the pursuit of fitness in local habitats. Next


Sociobiology, Status, and Parental Investment in Sons and.

Trivers hypothesisThe application of this hypothesis to contemporary societies has been widely accepted by sociobiolo‐gists, although it has received little actual empirical scrutiny. The Trivers‐Willard hypothesis is tested in this study using two nationally representative surveys of American adolescents and their parents. Across several. Can shed light on cultural behavior, including the behaviors of composing and telling stories. Where Darwinists interested in literary narrative might differ, however, is in the definition of what should be included in the category of literary narrative:, i.e., does literary narrative refer only to the fine arts or are stories told in tribal societies also examples of literary narrative? Another place where such Darwinists differ is in their view of the function of literary narrative. Those who focus on literature as fine art argue that literary narrative has a cognitive function. 22), as one example, argues that literary narrative satisfies a need, namely a desire for cognitive order. Sugiyama, for example, has argued that by substituting verbal representations for potentially costly first-hand experience, narrative enables an individual to safely and efficiently acquire information pertinent to the pursuit of fitness in local habitats. Sugiyama recognizes that stories have an effect on social behavior, the focus of her studies largely has been on ecological effects. What follows is solely about stories that concern social behavior and on one aspect of stories told in traditional societies which has not been a focus of Sugiyamas elegant studies; namely the fact that the stories are retold generation after generation and, in many cases, they are retold with little variation made in the story or the style used to tell the story. Evolutionary theory can generate many specific predictions about exactly what forms of social behavior are likely to be encouraged in traditional stories (particularly those told to children), and how this encouragement might be accomplished. Next


Reconsidering the null hypothesis Is maternal rank associated with.

Trivers hypothesisAbstract. Trivers and Willard hypothesized that vertebrates adaptively vary the sex ratio of their offspring in response to the mother's physical condition Trivers, R. L. & Willard, D. 1973 Science 179, 90–92. This hypothesis has produced considerable debate within evolutionary biology. Here we use meta-analysis. At a theoretical level, the Trivers-Willard Sex Ratio Hypothesis applies to both avian species and mammals. This article, however, conjectures that at the statistical level, sex ratio effects are likely to produce sharper numerical variations among birds than among mammals. We explain this greater statistical variation should likely have beneficial implications for increasing the efficiency of world-wide poultry egg (and perhaps also meat) production. A 30-minute invited talk summarizing the contents of this article was presented on June 18, 2017 at the Binghamton NEEPS-2017 Conference. The Version-1 June 27 (2017) draft of this paper was similar to the 30-minute talk I gave at Binghamton University, and it was disseminated nine days after this talk. Next


Trivers–Willard hypothesis revisited Does heat stress peri.

Trivers hypothesisObjective. To test the hypothesis that heat stress peri–insemination skews towards female the secondary sex ratio in dairy cattle. In addition, the effect of heat stress peri–insemination on birth weight of resultant calves was investigated. Methods. Data on the date of insemination and sex and birth weight of the resultant calf. This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. While some dismiss sociobiological theories as untestable, post hoc explanations, this article argues that sociologists should instead increase their efforts to identify and engage those theories that have novel empirical implications. Regarding parental investment, Triv‐ers and Willard use Darwinian reasoning to hypothesize that high‐status parents favor sons over daughters and that low‐status parents favor daughters over sons. The application of this hypothesis to contemporary societies has been widely accepted by sociobiolo‐gists, although it has received little actual empirical scrutiny. The Trivers‐Willard hypothesis is tested in this study using two nationally representative surveys of American adolescents and their parents. Across several different measures of investment, little evidence of the predicted parental investment behaviors is found. This article seeks not only to contribute to settling the empirical point at issue but also to encourage a renewed and empirically focused dialogue between sociologists and sociobiologists. Next


The Trivers–Willard hypothesis of parental investment No effect in.

Trivers hypothesisThe Trivers–Willard hypothesis TWH predicts that parents will bias their sex ratio toward sons when in good condition and toward daughters when in poor condition. Many human studies have tested the related hypothesis that parents' bias allocation of resources to existing sons and daughters according to the same. Formally proposed by Robert Trivers and Dan Willard, suggests that female mammals are able to adjust offspring sex ratio in response to their maternal condition, for example it may predict greater parental investment in males by parents in "good conditions" and greater investment in females by parents in "poor conditions" (relative to parents in good condition). The reasoning for this prediction is as follows: assume that parents have information on the sex of their offspring and can influence their survival differentially. While pressures exist to maintain sex ratios at 50%, evolution will favor local deviations from this if one sex has a likely greater reproductive payoff than is usual. Trivers and Willard also identified a circumstance in which reproducing individuals might experience deviations from expected offspring reproductive value—namely, varying maternal condition. In polygynous species males may mate with multiple females and low-condition males will achieve fewer or no matings. Parents in relatively good condition would then be under selection for mutations causing production and investment in sons (rather than daughters), because of the increased chance of mating experienced by these good-condition sons. Mating with multiple females conveys a large reproductive benefit, whereas daughters could translate their condition into only smaller benefits. An opposite prediction holds for poor-condition parents—selection will favor production and investment in daughters, so long as daughters are likely to be mated, while sons in poor condition are likely to be out-competed by other males and end up with zero mates (i.e., those sons will be a reproductive dead-end). Next


Trivers–Willard hypothesis - Infogalactic

Trivers hypothesisIn evolutionary biology and evolutionary psychology, the Trivers–Willard hypothesis, formally proposed by Robert Trivers and Dan Willard, suggests that female. The ability of parents to vary the sex ratios of their offspring is one of the most controversial topics in modern evolutionary and behavioral ecology. Part of my graduate research involves testing the predictions of a hypothesis that attempts to explain why deviations from a 50/50 sex ratio may occur. In many species, variance in reproductive success is greater in males than females. Under such conditions, Trivers and Willard suggested natural selection could favor deviations from a 50/50 sex ratio when maternal condition influences condition of young and when these differences carry over into adulthood and affect reproductive success. Females in superior condition are expected to favor sons, whereas females in average or poor condition should invest in daughters in order to contribute the maximum number of grandchildren to the following generation. Numerous studies in mammals have supported these predictions, but only recently has this hypothesis been applied to birds. Although recent studies suggest a relationship between maternal body condition and brood sex ratios in some passerine birds, there have been no manipulative or confirmatory experiments published. Therefore, my objective is to test Trivers and Willard’s hypothesis by manipulating body condition in female burrowing owls ( Burrowing owls are an excellent species to test the Trivers and Willard hypothesis because they lay large clutches (up to 12 eggs), which provides desirable statistical properties for detecting skews in sex ratios, and these owls nest in artificial burrow systems (ABS) in my study area, the Snake River Birds of Prey Area, which provides easy access to owls and their nests for measurements. Next


Trivers–Willard hypothesis revisited

Trivers hypothesisTrivers–Willard hypothesis revisited Does heat stress peri–insemination alter secondary sex ratio in crossbred dairy cattle? Physical attractiveness is heritable, then it follows that, over time, women become physically more attractive than men. The logic of the generalized Trivers-Willard hypothesis (g TWH) suggests that physically more attractive parents are more likely to have daughters than physically less attractive parents. As I explain in earlier posts, the data from both the National Longitudinal Study of Adolescent Health (Add Health) in the United States and the National Child Development Study (NCDS) in the United Kingdom confirm this prediction. Physically more attractive parents are significantly more likely to have a daughter as their first child than physically less attractive parents. physical attractiveness is heritable (such that beautiful parents beget beautiful children and ugly parents beget ugly children), then it logically follows that, over many generations in the course of human evolution, the average level of physical attractiveness among women should gradually increase and the average level of physical attractiveness among men should gradually decrease. No matter what the initial sex difference in physical attractiveness (whether men were more attractive than women, women were more attractive than men, or there were no sex differences in physical attractiveness), , the outcome should be that women are on average more physically attractive than men are. Earlier studies indeed show that women are on average physically more attractive than men both in Japan and in the United States. The analysis of the NCDS data replicates the sex difference in physical attractiveness in the United Kingdom. As the following graph shows, 85.5% of girls in the NCDS sample are described by their teachers at “attractive” at age 7, whereas only 83.1% of boys are. Next


Trivers-Willard hypothesis

Trivers hypothesisTHE TRIVERS-WILLARD HYPOTHESIS. "In species with a long period of parental investement after birth of young, one might expect biases in parental behavior toward offspring of different sex, according to the parental condition; parents in better condition would be expected to show a bias toward male offspring.". From an evolutionary point of view, sex differences in intergenerational transmission of income may be influenced by the Trivers-Willard (T-W) effect: Low status parents should invest more in daughters, whereas high status parents are expected to invest more in sons. This bias in parental investment may result in status-dependent sex biased parental support for higher education and educational attainment and should therefore affect the level of intergenerational income transmission for the sons and daughters. We used the data from the Wisconsin Longitudinal Study (WLS) to model the effect of parental financial investment on the child's income and educational attainment controlling for the number of siblings. The observed sex differences in intergenerational income transmission demonstrate that sons profited more from parental income and education in terms of their own income than daughters. Furthermore, we showed that fathers with a high socioeconomic index (SEI) invest more in their sons' education in terms of completed years of education and financial support during college. In contrast daughters of low SEI fathers completed more years of education and received more financial support than sons of low SEI fathers. However, the pattern in intergenerational income transmission might be better explained as a product of sociological factors and reproductive trade-offs in later life rather than as a consequence of the T-W effect. In modern western societies, access to resources is mainly determined by wealth that in turn is generated by income and to some degree by inheritance. Next


THE TRIVERS-WILLARD HYPOTHESIS -

Trivers hypothesisTHE TRIVERS-WILLARD HYPOTHESIS "In species with a long period of parental investement after birth of young, one might expect biases in parental behavior toward. The Trivers–Willard hypothesis (TWH) predicts that parents will bias their sex ratio toward sons when in good condition and toward daughters when in poor condition. Many human studies have tested the related hypothesis that parents' bias allocation of resources to existing sons and daughters according to the same principle. The present study used time diary and self-report data from the parents of 3200 children in the US to test the hypothesis that as status increases, parents will allocate more resources to sons vs. It finds no evidence that higher-status parents invest more in sons or that lower status parents invest more in daughters. This finding illustrates the specificity of situations in which the TWH effects should be expected. Only certain types of parental investment — such as protection and a bias in the sex ratio — may have been selected to vary according to parental condition. Optimal allocation of resources after the child is born, however, is achieved not by the simple bias predicted by the TWH, but by allocating resources among offspring in ways that yield the largest marginal inclusive fitness gains. Next


Robert Trivers - Wikipedia

Trivers hypothesisTrivers–Willard hypothesis; References External links. Wikiquote. Robert Trivers Official website; Rutgers School of Arts and Sciences. So I was surprised when, on August 27, a deputy managing editor of the National Review—a conservative magazine that has published numerous evolution deniers—cited evolutionary theory as a reason that women should vote for Willard Mitt Romney for president. Williamson wrote, “It is a curious scientific fact (explained in evolutionary biology by the Trivers-Willard hypothesis—Willard, notice) that high-status animals tend to have more male offspring than female offspring, which holds true across many species, from red deer to mink to Homo sap.” Williamson notes that Romney has five sons, a bunch of male grandsons and is “basically a tribal chieftain.” And Barack Obama? Of the Trivers-Willard hypothesis and numerous other groundbreaking propositions that have made Trivers a legendary character in evolutionary theory and “one of the great thinkers in the history of Western thought,” according to experimental psychologist and popular author Steven Pinker of Harvard University. But most Americans do not accept evolution, and the percentage is even lower among conservatives. And fallopian tubes.” Based on the sex ratios of the two men's progeny, he then concludes, “From an evolutionary point of view, Mitt Romney should get 100 percent of the female vote. He should get Michelle Obama's vote.” So I called Robert Trivers. I told Trivers that Williamson's article tried to make the case from Trivers-Willard that all women should vote for Romney. ” In their 1973 paper Trivers and Willard sum it up: “Natural selection should favor parental ability to adjust the sex ratio of offspring produced according to parental ability to invest,” with investment including all care for the progeny, from fertilized egg to independence. “The best evidence was in red deer,” Trivers explained on the phone, “where dominant females produce 60 percent sons. They're two different decisions.” Just as an exercise, Trivers did some analysis of Trivers-Willard in regard to Romney and Obama: “There's no way of looking at the sex ratios of progeny of these two couples and predicting anything about their relative superiority over time. But investment in mammals has a simple logic because usually the male ain't doing s—.” In this polygynous species, where a single male's harem can number 20 females, a dominant female's strong sons have a big advantage over weaker males that may spend their lives nookie-free. It would be better put as an evolutionist arguing about the five-versus-two ratio [of the total number of children born to each candidate]. That's so obvious we don't need to talk about the sex ratio of the progeny. When he stopped laughing, Trivers continued, “Maybe the guy should be saying that all women should try to f— [Romney]. But then he [Williamson] wants to double down: hey, he [Romney] produced five sons, so that proves he's the ultimate on that side of the coin. But by the same logic there's an ultimate on the other side of the coin who's a female specialist. If Obama had five girls, then we could line it up and see that they [the total number of progeny over the long term] are identical.” Williamson's invocation of Trivers-Willard would thus allow for a more balanced analysis if Romney were running for mayor of Anatevka against Fiddler on the Roof's Tevye “I have five daughters” the Milkman. Next


The Trivers-Willard hypothesis - The Panda's Thumb

Trivers hypothesisAug 23, 2004. One of the most debated hypotheses in evolutionary biology received new support today, thanks to a study by a scientist at the University of Nevada, Reno. Elissa Cameron, a mammal ecologist in the Department of Natural Resources and Environmental Science, has helped to disprove critics of a scientific. That her reproductive organs also know best may come as more of a surprise. But that is what two evolutionary biologists, Robert Trivers and Dan Willard, hypothesised nearly four decades ago. Boys, they reasoned, will thrive reproductively when they have grown big and strong in resource-rich environments. Girls, by contrast, will do reasonably well across the board and thus have a comparative advantage over their brothers in poorer situations. Parents, meanwhile, have a genetic incentive to see their progeny do well. Give a mother abundant resources, then, and her body should favour sons. Place her in difficult conditions and she should have more daughters. The Trivers-Willard theory has been tested with success in several species of wild animal. Showing it to be true in people, however, has proved difficult. Next


Probably Overthinking It Does Trivers-Willard apply to people?

Trivers hypothesisMay 17, 2016. Today I am working on another "one-day paper", although this one is a bit of a cheat, since I'm a few hours past the deadline. Nevertheless, the question of the day is whether the Trivers-Willard effect applies to people. According to Wikipedia, the Trivers-Willard hypothesis ".suggests that female mammals. The Trivers–Willard hypothesis (TWH) predicts that parents will bias their sex ratio toward sons when in good condition and toward daughters when in poor condition. Many human studies have tested the related hypothesis that parents' bias allocation of resources to existing sons and daughters according to the same principle. The present study used time diary and self-report data from the parents of 3200 children in the US to test the hypothesis that as status increases, parents will allocate more resources to sons vs. It finds no evidence that higher-status parents invest more in sons or that lower status parents invest more in daughters. This finding illustrates the specificity of situations in which the TWH effects should be expected. Only certain types of parental investment — such as protection and a bias in the sex ratio — may have been selected to vary according to parental condition. Next


The Trivers-Willard hypothesis of parental investment No effect in.

Trivers hypothesisSep 1, 2001. The Trivers-Willard hypothesis TWH predicts that parents will bias their sex ratio toward sons when in good condition and toward daughters when in poor condition. Many human studies have tested the related hypothesis that parents' bias allocation of resources to existing sons and daughters according. Is renowned for its ability to change color from a sparkling emerald to a deep brown. Surprisingly, we don’t really know what factors determine whether a particular lizard chooses to be green or brown at a particular time. 279-281; I’ve omitted most references here): “In theory, we might expect green anoles to match their background, turning green when in vegetation and brown when against a woody surface. Although widely believed, this idea is not strongly supported (reviewed in Jenssen et al., , 1990] for an opposite result). Indeed, males of green species often adopt a bright green coloration when in the survey posture, although a darker appearance would almost surely be more cryptic against a woody background; this tendency suggests the possibility that skin color is being used to make the lizards more, rather than less, conspicuous (e.g., Macedonia’s work on on the Japanese island of Chichi-Jima has tried to take this further. By noting the color of 169 anoles encountered in the field, Yabuta and Suzuki-Watanable tried to look for correlates of color. Next


Trivers-Willard Hypothesis - Journal of Dairy Science

Trivers hypothesisAccording to the Trivers-Willard hypothesis, maternal condition at or around conception affects the secondary sex ratio in mammals. However, there are little or no data available on indicators of maternal condition in dairy cows on the sex of the resultant offspring. A total of 76,607 body condition score BCS; scale of 1 to 5. The sample size consisted of 740 British nulliparous women (i.e., yet to have any children) who agreed to provide detailed information about their diets at three stages, namely preconception (covering one year), and early and late gestation. Johnson, and Andrew Neil investigated women's diets prior to falling pregnant to gauge whether it might have an effect on the sex of the offspring. It is important to note that the mothers did not know the sex of their babies except a few who found out this information through amniocentesis or because of abnormal scans. That said this information only occurred later in the pregnancy so for the preconception and early pregnancy data, women were indeed blind to the sex of their child (and hence they did not alter their diets as a response to such information). The goal was to test the Trivers-Willard hypothesis, which posits that depending on specific parental and/or environmental conditions, natural selection should favor: (1) biased offspring sex ratio; (2) biased differential investment in sons and daughters postnatally. Note that the Trivers-Willard hypothesis posits that given the greater reproductive variance of males, when conditions are good, it makes evolutionary sense to have biased investments toward males. paper, the objective was to test whether the richness of a woman's diet would augment the likelihood of producing sons (i.e., a biased offspring sex ratio). I shall only report on the preconception data for they are the ones relevant to testing biased offspring sex ratio. The nutritional data was factor-analyzed and two key factors emerged, namely factor 1 captured diets possessing high nutrient levels (protein, fat, Vitamin C, folate, and several minerals including iron, zinc, and potassium) whereas factor 2 corresponded to diets rich in Vitamin A (retinol) and Vitamin B12. Next


Sociobiology, Status, and Parental Investment in Sons and. - Jstor

Trivers hypothesisStatus parents favor sons over daughters and that low-status par- ents favor daughters over sons. The application of this hypothesis to contemporary societies has been widely accepted by sociobiolo- gists, although it has received little actual empirical scrutiny. The. Trivers-Willard hypothesis is tested in this study using two. Mother's milk may be the first food, but it is not created equal. In humans and other mammals, researchers have found that milk composition changes depending on the infant's gender and on whether conditions are good or bad. Understanding those differences can give scientists insights into human evolution. Researchers at Michigan State University and other institutions found that among 72 mothers in rural Kenya, women with sons generally gave richer milk (2.8 percent fat compared with 0.6 percent for daughters).* Poor women, however, favored daughters with creamier milk (2.6 versus 2.3 percent). These findings, published in the American Journal of Physical Anthropology in September, echo previous work that showed milk composition varying with infant gender in gray seals and red deer and with infant gender and the mother's condition in rhesus macaques. The new study also follows findings that affluent, well-nourished moms in Massachusetts produced more energy-dense milk for male infants. Together the studies provide support for a 40-year-old theory in evolutionary biology. The Trivers-Willard hypothesis states that natural selection favors parental investment in daughters when times are hard and in sons when times are easy. Next


Trivers-Willard sex ratio or investment

Trivers hypothesisThe Trivers–Willard hypothesis has commonly been considered to predict two things. First, that a mother in good condition should bias the sex ratio of her offspring towards males if males exhibit greater variation in reproductive value. Second, that a mother in good condition should invest more per son than per daughter. Partible paternity, the belief that a child can have more than one biological father, is widespread in lowland South America. An analysis of demographic data sets from four lowland tribes (Aché, Barí, Ese Eja, and Surui) reveals a systematic variation in the sex ratios of live births with respect to the number of fathers to whom the births are attributed. Births attributed to only one father show a sex ratio that is unexceptional for South America; births with two fathers are highly male biased, while children with three or more are female biased. This pattern may be a manifestation of a phenomenon predicted by the Trivers-Willard hypothesis, which proposes that, in many circumstances, females in good condition might bias their offspring toward males, while those in poor condition would produce a preponderance of females. If, as suggested below, a woman with a husband and a single extramarital lover tends to be better cared for before and during a pregnancy than other women, this difference might result in the improved maternal condition required by the Trivers-Willard hypothesis for excess males, while women who accept two or more lovers might be preponderantly those who are already in distress, thus tending to produce female biased offspring. Next


A Trivers-Willard Effect in Contemporary Humans Male-Biased Sex.

Trivers hypothesisJan 14, 2009. Natural selection should favour adaptive variation in offspring sex ratio if alterations maximise the offspring's potential reproductive success Trivers-Willard hypothesis, TWH; 1. For species where one sex has more variable reproductive success males in polygynous species, the TWH predicts that 1 a. The Trivers-Willard hypothesis (TWH) predicts that parents will bias their sex ratio toward sons when in good condition and toward daughters when in poor condition. Many human studies have tested the related hypothesis that parents' bias allocation of resources to existing sons and daughters according to the same principle. The present study used time diary and self-report data from the parents of 3200 children in the US to test the hypothesis that as status increases, parents will allocate more resources to sons vs. It finds no evidence that higher-status parents invest more in sons or that lower status parents invest more in daughters. This finding illustrates the specificity of situations in which the TWH effects should be expected. Only certain types of parental investment - such as protection and a bias in the sex ratio - may have been selected to vary according to parental condition. Optimal allocation of resources after the child is born, however, is achieved not by the simple bias predicted by the TWH, but by allocating resources among offspring in ways that yield the largest marginal inclusive fitness gains. TY - JOURT1 - The Trivers-Willard hypothesis of parental investment T2 - Evolution and Human Behavior AU - Keller, Matthew C. AU - Hofferth, Sandra PY - 2001/9/1Y1 - 2001/9/1N2 - The Trivers-Willard hypothesis (TWH) predicts that parents will bias their sex ratio toward sons when in good condition and toward daughters when in poor condition. Many human studies have tested the related hypothesis that parents' bias allocation of resources to existing sons and daughters according to the same principle. Next


What Is The Trivers-Willard Hypothesis? What Evide.

Trivers hypothesisThe Trivers-Willard Hypothesis was stated in 1973 by R. L. Trivers and D. E. Willard which stated that- " In species with a long period of parental investement after birth of young, one might expect biases in parental behavior toward offspring of diffe. view the full answer. According to popular belief, whether you have a baby girl or boy is purely a matter of chance. And yet, a study published several years ago shows that mothers in stressful jobs, for instance, give birth to more girls than boys. The correlation between such shifts in the offspring sex ratio and the mother's overall state is something that evolutionary biologists are familiar with from other animal species. One influential hypothesis puts natural selection as an explanation for the imbalances observed. Strong males with high reproductive success The Trivers-Willard hypothesis states that it is beneficial for mothers to be able to adjust the sex of their offspring in response to their own state of health. Accordingly, a female in good condition should give birth to more male offspring. This is because successful males have the potential to produce more children in their lifetime than successful females. By producing strong sons, healthy mothers increase the probability of their own genes being widely distributed. Next


The Trivers-Willard hypothesis

Trivers hypothesisThe Trivers-Willard hypothesis states that when conditions are good, parents have more male offspring; and when conditions are poor, parents have more female offspring. Luke Jostins reported this from a conference last year, so not too surprising. Evidence of widespread selection on standing variation in Europe at height-associated SNPs. Let me jump to the summary: In summary, we have provided an empirical example of widespread weak selection on standing variation. We observed genetic differences using multiple populations from across Europe, thereby showing that the adult height differences across populations of European descent are not due entirely to environmental differences but rather are, at least partly, genetic differences arising from selection. Height differences across populations of non-European ancestries may also be genetic in origin, but potential nongenetic factors, such as differences in timing of secular trends, mean that this inference would need to be directly tested with genetic data in additional populations. Next


The Trivers–Willard hypothesis sex ratio or investment? - NCBI - NIH

Trivers hypothesisApr 18, 2016. The Trivers–Willard hypothesis has commonly been considered to predict two things. First, that a mother in good condition should bias the sex ratio of her offspring towards males if males exhibit greater variation in reproductive value. Second, that a mother in good condition should invest more per son. The Trivers–Willard hypothesis (TWH) predicts that in a polygynous mating system, when fitness of male offspring is more variable than fitness of female offspring, mothers should invest more heavily in the sex with the highest marginal fitness returns. Females in good condition or high social rank should benefit by investing in sons, and females in poor condition or low social rank should benefit by investing in daughters. Many empirical studies have tested different aspects of the TWH, but no study has tested the assumptions and predictions in a single polygynous species using measures of maternal condition and maternal social rank, while accounting for random effects that can also influence offspring growth and survival. Here, we followed individuals in an isolated population of pronghorn on the National Bison Range, Montana, over multiple generations and tested the assumptions and predictions of the TWH. Pronghorn females who were in good condition or were socially dominant weaned larger fawns that were in better condition, but this advantage did not increase male fawn survival or reproductive success. Next


Trivers hypothesisTheory. The concept of "reciprocal altruism", as introduced by Trivers, suggests that altruism, defined as an act of helping another individual while incurring some. The Trivers-Willard hypothesis states that when conditions are good, parents have more male offspring; and when conditions are poor, parents have more female offspring. The thinking behind this is that in favourable conditions males will be able to mate with many females before they die and have a greater chance of passing on their genes; and when conditions are poor males will not be able to mate with as many females and are more likely to be out-competed, and therefore a female will have more chance of passing on genetic material than any particular male. The Trivers-Willard hypothesis seems to hold true for human beings. In a study of the Forbes Billionaires List it was found* that the children of billionaires were 60% male, and if only male billionaires were considered then this percentage rose to 65%. The effect was the same whether the billionaires were self-made or had inherited their fortunes, suggesting that if there was a biological reason for success in business it was not relevant in selecting the sex of offspring. Next


The Maternal Dominance Hypothesis Questioning Trivers and Willard

Trivers hypothesisThirty years ago, Trivers and Willard 1973 hypothesized that parental “condition” could be central in influencing the sex ratio of offspring, “good condition” being associated with the conception of males. However, I argue that “condition” is a distraction in this otherwise useful hypothesis, because it is merely a frequent. Mother's milk may be the first food, but it is not created equal. In humans and other mammals, researchers have found that milk composition changes depending on the infant's gender and on whether conditions are good or bad. Understanding those differences can give scientists insights into human evolution. Researchers at Michigan State University and other institutions found that among 72 mothers in rural Kenya, women with sons generally gave richer milk (2.8 percent fat compared with 0.6 percent for daughters).* Poor women, however, favored daughters with creamier milk (2.6 versus 2.3 percent). These findings, published in the American Journal of Physical Anthropology in September, echo previous work that showed milk composition varying with infant gender in gray seals and red deer and with infant gender and the mother's condition in rhesus macaques. Next


Trivers–Willard hypothesis Zoology

Trivers hypothesisA presentation about the Trivers–Willard hypothesis in english. by melinte_andrei_1 One of the most debated hypotheses in evolutionary biology received new support today, thanks to a study by a scientist at the University of Nevada, Reno. Elissa Cameron, a mammal ecologist in the Department of Natural Resources and Environmental Science, has helped to disprove critics of a scientific theory developed in 1973. At that time, ecologist Bob Trivers and mathematician Dan Willard said that large healthy mammals produce more male offspring when living in good conditions, such as areas where there is an ample food supply. Conversely, female mammals living in less desirable conditions would tend to have female offspring. She conducted an analysis of 1,000 studies that examined the Trivers-Willard hypothesis and sex ratios in mammals. Her study found that female mammals that were in better body condition during the early stages of conception were more likely have male offspring. Body fat and diet can affect levels of glucose circulating in a mammal’s body, and Cameron suggests that the levels of glucose around the time of conception could be influencing the sex of the animal’s offspring. “A high-fat diet can result in higher levels of glucose, thereby supporting the hypothesis that glucose may be contributing to the sex of the mammal’s offspring,” Cameron said. Evolutionary theory predicts that mothers of different condition should adjust the birth sex ratio of their offspring in relation to future reproductive benefits. Next


The Trivers-Willard Hypothesis - YouTube

Trivers hypothesisDec 9, 2016. An investigation of sex ratios at birth for humans Final Project for SLS 12 Understanding Darwinism. PROBLEM: In 1973, evolutionary biologists Robert Trivers and Dan Willard famously posited that parents prefer their sons when times are good and their daughters when times are tough. Few studies, however, have put forth biological proof to support this hypothesis. METHODOLOGY: Researchers led by Michigan State University's Masako Fujita assessed the breast milk and feeding frequencies of 83 Kenyan mothers who raise around six children, on average, and live in villages where men can have multiple wives. They controlled for several factors, including age and dietary fat intake. RESULTS: The moms with less land and fewer livestock produced fattier milk for their daughters than for their sons, and also fed them more frequently. Wealthier mothers, on the contrary, appeared to favor their sons over their daughters. CONCLUSION: Poor mothers place a larger biological investment in their daughters than their sons. IMPLICATION: As Trivers and Willard previously suggested, less privileged moms may provide more resources to their daughters, since they stand a greater chance of increasing their status through their child's marriage this way. Next


Testing the Trivers-Willard Hypothesis - Frontiers

Trivers hypothesisFrom an evolutionary point of view, sex differences in intergenerational transmission of income may be influenced by the Trivers-Willard T-W effect Low status parents should invest more in daughters, whereas high status parents are expected to invest more in sons. This bias in parental investment may result in. Examples of memes are tunes, ideas, catch-phrases, clothes fashions, ways of making pots or of building arches. Just as genes propagate themselves in the gene pool by leaping from body to body via sperms or eggs, so memes propagate themselves in the meme pool by leaping from brain to brain via a process which, in the broad sense, can be called imitation. Humphrey neatly summed up an earlier draft of this chapter: `... If a scientist hears, or reads about, a good idea, he passed it on to his colleagues and students. If the idea catches on, it can be said to propagate itself, spreading from brain to brain. memes should be regarded as living structures, not just metaphorically but technically.(3) When you plant a fertile meme in my mind you literally parasitize my brain, turning it into a vehicle for the meme's propagation in just the way that a virus may parasitize the genetic mechanism of a host cell. And this isn't just a way of talking -- the meme for, say, "belief in life after death" is actually realized physically, millions of times over, as a structure in the nervous systems of individual men the world over.' So far, I have not talked much about man in particular, though I have not deliberately excluded him either. Part of the reason I have used the term `survival machine' is that `animal' would have left out plants and, in some people's minds, humans. Next


Trivers willard hypothesis definition of

Trivers hypothesisDefinitions of trivers willard hypothesis, synonyms, antonyms, derivatives of trivers willard hypothesis, analogical dictionary of trivers willard hypothesis English In its broad sense, the term "evolutionary psychology" stands for any attempt to adopt an evolutionary perspective on human behavior by supplementing psychology with the central tenets of evolutionary biology. The underlying idea is that since our mind is the way it is at least in part because of our evolutionary past, evolutionary theory can aid our understanding not only of the human body, but also of the human mind. In this broad sense, evolutionary psychology is a general field of inquiry that includes such diverse approaches as human behavioral ecology, memetics, dual-inheritance theory, and Evolutionary Psychology in the narrow sense. The latter is a narrowly circumscribed adaptationist research program which regards the human mind as an integrated collection of cognitive mechanisms that guide our behavior and form our universal human nature. These cognitive mechanisms are supposed to be adaptations—the result of evolution by natural selection, that is, heritable variation in fitness. Next


Trivers-Willard hypothesis Psychology

Trivers hypothesisTrivers and Willard also identified a circumstance in which reproducing individuals might experience deviations from expected offspring reproductive value namely, varying maternal condition. In polygynous species males may mate with multiple females and low-condition males will achieve fewer or no matings. The very insightful Trivers-Willard hypothesis, proposed in the early 1970s, states that females in good physiological condition are more likely to produce male offspring when the variance of reproductive success among males is high. The hypothesis has inspired a number of studies over the last three decades aimed at its experimental verification, and many… Variation in gmax, the maximum value of g at which the T strategy can go to ®xation, as a function of R. The four different curves correspond to d 1:5 (solid diamond), d 2:0 (solid square), d 3:0 (solid triangle) and d 5:0 (cross). Next


A comprehensive test of the Trivers–Willard hypothesis in pronghorn.

Trivers hypothesisOct 28, 2015. Abstract. The Trivers–Willard hypothesis TWH predicts that in a polygynous mating system, when fitness of male offspring is more variable than fitness of fem. The thrifty phenotype hypothesis says that reduced fetal growth is strongly associated with a number of chronic conditions later in life. This increased susceptibility results from adaptations made by the fetus in an environment limited in its supply of nutrients. The thrifty phenotype is a component of the Fetal Origins Hypothesis. These chronic conditions include coronary heart disease, stroke, diabetes, and hypertension. Proponents of this idea say that in poor nutritional conditions, a pregnant woman can modify the development of her unborn child such that it will be prepared for survival in an environment in which resources are likely to be short, resulting in a thrifty phenotype (Hales & Barker, 1992 The thrifty phenotype hypothesis suggests that early-life metabolic adaptations help in survival of the organism by selecting an appropriate trajectory of growth in response to environmental cues. Next