Analysis of a large sample of single and fraternal twins, living in the UK, allowed us to estimate the degree of heritability (genetic conditions) differences in conscious preferences in choice of marriage partner. We studied the relationship of people to the 13 selection criteria (kindness, intelligence, health, attractiveness, education, religiosity, etc.).
It turned out that about 20% of individual differences in the evaluation of these criteria are determined by genes and not environment.
In another study on Australian twins, it was shown that the realized heritability of mating preferences on such criteria, is negligible.
It turns out that genes affect our desires are stronger than their implementation — probably because the acquisition of the perfect marriage partner one desires is not enough. The findings are preliminary, and should not be extended to all selection criteria for a life partner.
Sexual selection leads not only to the development of adaptations that provide sex appeal and success in competition for sexual partners. An equally important aspect is the evolution of the matrimonial preferences, i.e. criteria by which individuals choose their partners. For these preferences to evolve, they must be subject to genetic variation.
Oddly enough, we still know very little about such variability in natural populations of animals. In most studies, like the default that the preferences of all individuals "choosing" sex (typically females) are approximately equal, and the task is to identify and describe.
Meanwhile it is known that mating preferences are mutable: they can vary not only from individual to individual, but one and the same individual depending on age, phase of reproductive cycle, the physical and mental state .
The question of to what extent the variability of mating preferences depends on genes and environment and life experience, almost unknown. And without any assessment of the impact of sexual selection on the evolution of the studied population will be at best inaccurate.
To fill this gap one of the most convenient features is a man — not least due to the fact that people can just ask about their preferences, instead of having cumbersome and costly behavioral experiments or long-term monitoring of animals in nature (the results of which, incidentally, is not always be more reliable than survey data). The reliability of the conclusions in these studies greatly depend on the sample size, and interview 4,000 people immeasurably easier than, for example, to monitor the mating behavior of peacocks 4000.
To clarify the question of the heritability of mating preferences in humans biologists and psychologists from the UK and Australia have used the classical twin method. Estimated the so-called "heritability in the broad sense" (broad-sense heritability), that is, the proportion of variability in the studied trait due to genetic differences between individuals, and not by the environment and random factors .
Twin method is based on a comparison of the trait in pairs of identical (monozygotic) and nonidentical (dz) twins. Identical twins have identical genes, non-identical absolutely identical on average, only half of the genome, and the second half can be the difference. Therefore, if variation in this trait has a genetic component, identical twins should be on average more similar to each other in this trait than non-identical.
There is a very sophisticated, elaborated and repeatedly proven statistical methods based on the comparison of correlations in identical and non-identical twin pairs to decompose the observed variability into three parts, each assessing quantitatively:
1) variability-dependent genes (this is, in fact, is the desired value of heritability of the trait),
2) variability, depending on environmental factors common to twins, one pair (this includes the conditions of fetal development, and in the family environment and the influence of parents),
3) variability, depending on environmental conditions, different for twins from the same pair, and from all sorts of random factors, including errors made by researchers when measuring trait .
The authors have studied a large sample of twins living in the UK. The study involved 4586 twins, including 1763 full and 1060 pairs of "individuals" whose sisters or brothers, for whatever reasons were not included in the sample. Singles such studies are useful to improve the accuracy of some statistical indicators. Identical and non-identical twins in the sample were roughly equal. The majority (88%) of the participants were women (those twins originally picked up to explore some female hereditary diseases). Data for men and women were treated separately because there was no reason to assume that the heritability of mating preferences should be the same in both sexes. Opposite-sex couples was only 16, and the twins from these pairs was seen as a "loner".
All participants were asked to rank the 13 qualities of a potential partner in the descending order of their importance. In the task it was emphasized that we are talking about criteria of choosing a spouse or partner for a lasting relationship, not a fleeting connection. Characteristics were the following:
kindness and understanding, flexible, easy character, intelligence, health, attractiveness, brightness of personality, the desire to have children, the ability to earn good money, creativity, artistry, thrift, good genetics, University degree, religiosity.
One of the drawbacks of the technique is that it is not always possible to understand the direction of preferences. For example, in the case of health, this direction is obvious: a healthy companion of life is certainly preferable to the patient for most respondents. However, in the case of religiosity and the desire to have children, the situation is not so obvious.
Then the order in which participants placed these signs, is generally consistent with the results of many studies performed in different countries. Both sexes considered the most important criterion of "kindness and understanding". For both sexes important was the ease of character, intelligence, health and attractiveness, while good heredity, University education and religiosity did not receive high ratings.
Statistical analysis revealed significant differences between male and female estimates of some criteria. More important for women than for men, such a quality partner as kindness, desire to have children and the ability to earn good money. Men give more importance to visual appeal, thrift, creative inclinations and brightness of personality.
The assessment of many traits changes with age. The older the Respondent, the higher on average he values in a partner kindness, religiosity (or lack thereof), thrift, good heredity, earning capacity, intelligence and health. The importance of easy nature and bright personality decreases with age. Evaluation of some characteristics different changes with age in men and women. For example, attractiveness becomes less important for women but not for men. Good heredity and the ability to earn with age become more important in the eyes of women and lose value in the eyes of men. The importance of the desire to have children and thrift increases with age in men but remained constant in women.
Between the estimates of certain characteristics showed a weak correlation: those who highly value attractiveness, on average, give slightly smaller values of kindness and the importance of the mind is positively correlated with the importance of University education. But all the found correlation is very weak, so the authors considered the 13 symptoms as independent.
For all 13 indicators in women and 12 in men, the similarity of identical twins was higher than for non-identical (the only exception is the rating of the importance of the criterion of "goodness" of men). This suggests the presence of hereditary (genetic) component to variability in mating preferences.
Thoroughly statistical analysis revealed significantly non-zero heritability of female preference on kindness, health, physical attractiveness, brightness of personality and ability to earn. The maximum heritability (0,30) are shown for the relationship of women to the physical attractiveness of the partner. Relation to the other criteria, most likely, also depends on genes, but to the level of statistical significance these results are "not held". Of the 13 criteria less genes affect women's attitudes towards thrift partner (the heritability of 0.05). But the attitude towards thrift, and the partner's mind, the small but significant influence of the family (for other preferences, the influence of the family turned out to be false).
Men have a preference, apparently, are also partly hereditary, but due to the small number of men in the sample a level of statistical significance was reached only in two cases (economic and religious). Significant effect of family on the marriage preferences of men were not identified.
If you combine all 13 signs in one complex, it turns out that the heritability of mating preferences in women 0.20 (high confidence level), in men and 0.19 (on the verge of reliability). The differences in accuracy in this case is clearly not determined by different heritability, and the fact that men in the sample was 8 times less than women.
This study is largely innovative. The authors have invaded an area hitherto almost unknown. For final conclusions and reliable interpretations will need many more such works. Nevertheless, the authors first received convincing data on the existence in humans of genetic variation in several criteria of choice of marriage partner. In addition, they showed that the relative importance of the different criteria also may be subject to genetic variation: some more appreciate the mind, than beauty, someone-on the contrary, these differences are also partly determined by genes.
This result is obtained for the first time not only for humans but for all animals. It is known that animals when choosing a mate, usually take into account not one but many different criteria.
However, models that take into account several selection criteria, only starting to be developed by specialists in sexual selection. For such models, the obtained result is of great importance.
In 2011 on a large sample of Australian twins and their spouses were studied realized heritability of mating preferences (Zietsch et al., 2011). In other words, compared not abstract desire twins, as in the work being discussed, and their real spouses.
The comparison was performed on the set of attributes: height, weight, education, income, personality traits, religiosity, attitude to different social problems. The heritability for most of the criteria were close to zero. That is, the husbands of identical twin sisters were not more similar to each other on all these grounds than men non-identical sisters.
It turns out that a hereditary component is present in the mating preferences and identified in the work being discussed, almost never seen when it comes to real marriages. This is understandable: because in order to get the "perfect" husband, one desire is not enough.
Any kind of who are inclined to monogamy, the creation of breeding pairs is influenced by the preferences of both parties, and the extent to which each of them corresponds to the preferences of the other. Little to dream about the intelligent and kind husband, you also need to possess those qualities that are valued intelligent and kind men.
Of course, in a real marriage affects many other factors in addition to personal qualities and preferences of the partners. We should not forget that preferences may change depending on circumstances .
One of the clear patterns identified in the 2011 (and also in some earlier studies), is a positive assortatively marriages, that is, the tendency of people to marry partners similar to them on a number of grounds (such as age, religiosity, education, height, weight, attitude toward birth control, immigrants from Asia, etc.). Many of these symptoms partly depend on genes. For example, the heritability of body weight in the Australian sample is equal to 0.68, the education level and 0.43, religiosity and attitude to different social problems around 0.30. It has been shown that increased similarity of spouses on these grounds largely due to the initial choice than "re-education" in the process of living together.
You may notice that between the positive assortatively marriages on hereditary characteristics and the lack of realized heritability of mating preferences is a contradiction. It would seem that from the first it follows that in the selection of a spouse must also be a hereditary component. We hope that further studies will clarify this confusing issue, the study of which is only beginning.
In order to assess the strength and nature of sexual selection in modern human populations, you must also find out whether individual differences in mating preferences on reproductive success. You may think that zero realized heritability of preferences excludes the possibility of such influence, but it is not. Even if the actual choice of a spouse do not depend on genetically determined preferences, they still may depend on the quantity and quality of children. For example, it is known that females of some animals invest in offspring less of their resources or allocate resources unevenly between sons and daughters, if children are conceived by poor quality or unsuitable male .
To avoid incorrect interpretations it is necessary to understand that it shows the magnitude of heritability of the trait. It shows, does it depend on the genes available in the population variability in this trait, not a symptom at all."
The sign itself (e.g. the tendency of people to appreciate in a partner kindness) can be hard enough already "written" in the genome, but the genes influencing this trait, may be the same for all modern people. In this case, the characteristic will have a zero heritability. Such sign may not evolve here and now, but that doesn't mean it hasn't evolved in the past. On the contrary, low genetic variation should be characteristic of the signs that strongly influence the adaptation because selection favours variants of one sign and eliminating the other, systematically reduces genetic variation. The variability, after which it will remain in the population, will depend largely on the environment, not from genes.
Therefore, the most important of our signs, and were subjected to intense selection in our ancestors, in modern humanity may have zero heritability.
This means that the results of the research in question helps to understand how sexual selection operates in contemporary human populations, but for the reconstruction of past evolutionary events can be applied only with great caution.published