Sexual Selection Under Parental Choice

The Evolution of Human Mating Behavior

Menelaos Apostolou

• Publisher: Psychology Press
• Year: 2013
• ISBN:
  9781135009489
• Edition: 1
• Topic: Psychology
• Subtopic: Social Psychology
• Index: Psychology

Parents often disagree with their children over their choice of partner. Although the reasons may vary the outcome is very often one of conflict – a conflict peculiar to the human species. For the first time in one volume, Sexual Selection under Parental Choice employs an evolutionary perspective to understand this conflict and explore its implications.

Covering recent developments in the field of evolutionary psychology, Menelaos Apostolou reveals the extent of parental attempts to control the mating decisions of their offspring and investigates the qualities parents seek in prospective in-laws. Children's attempt to escape this control can lead to practices such as foot-binding and clitoridectomy or, in postindustrial societies, more subtle forms of coercion and manipulation. Apostolou demonstrates that much of human mating behavior has been shaped by parental choice and that parents have a significant influence in sexual selection: the traits they favour in their children's mates are selected and increase in frequency in the population.

Sexual Selection under Parental Choice will be ideal reading for researchers and advanced students of evolutionary, developmental and social psychology, as well as other related disciplines such as social anthropology, sociology and the biological sciences.

1

PARENT–OFFSPRING CONFLICT OVER MATING

The Evolutionary Roots of Romeo and Juliet's Story

In the popular Hollywood film Cocktail a young woman from a wealthy family (Elisabeth Shue) falls for a young and attractive bartender (Tom Cruise). This relationship meets with strong opposition from the woman's father who, not impressed by the young man's looks and upset by the low socioeconomic status of his prospective son-in-law, goes so far as to denounce his daughter in order to prevent the marriage. In Shakespeare's play Romeo and Juliet the titular protagonists, who are madly in love, meet a tragic end as a consequence of their families' fierce opposition to their relationship. In Samuel Richardson's novel Clarissa the main character is forced by her family to marry a man whom she finds physically repulsive.

These fictional stories reflect the reality that the mate choices of children do not always meet with the approval of their parents. In turn, this raises a question about the roots of this disagreement. One possible answer is that parents want the best for their children, who are young and inexperienced and thus prone to make the wrong choices. Parents, therefore, intervene in order to enable their daughters and sons to take corrective action.

At first, this explanation sounds plausible, and it certainly has a grain of truth. People, especially the young, make mistakes, and those who love and care for them point out these mistakes and prompt them to correct their ways. This being the case, however, we would expect parental involvement to primarily take the form of advice. This is generally the case in Western societies, but not in non-Western or historical ones. In particular, in the majority of preindustrial societies parents do not have a merely advisory role, but actively choose spouses for their children and force their choices upon them through the institution of arranged marriage (Apostolou, 2007b, 2010e). For instance, among the Naskapi foragers in Canada: “Parents gave away their daughters in marriage without any ceremony, and without much consideration for their wishes” (Jenness, 1977, p. 273).

This has also been the case in historical societies. For example, in pre-Victorian England:

Elizabeth, daughter of Agnes Paston, obstinately insisted in choosing her own husband. To bring her to heel, her mother put her in virtual solitary confinement, forbidden to speak either to visitors or to male servants. In addition, “she hath since Easter the most part been beaten once in the week or twice, and sometimes twice on a day, and her head broken in two or three places.”

(Stone, 1990, p. 130)

In marriage arrangements parents aim to form beneficial alliances, rather than choose the best spouses for their daughters and sons, and they employ a variety of methods in order to make control over mating possible, including some which are brutal, such as female circumcision and foot-binding (see Chapter 5).

It seems, then, that parents are not so much interested in advising their children as in controlling their mate choices. In turn, this hints that parents' and children's interests regarding mate choice do not overlap. Why is this so? The answer that I put forward in this chapter is based on evolutionary logic and the fact that parents and children are not genetically identical.

Parent—Offspring Conflict

In the evolutionary perspective, individual organisms are viewed as vehicles which transfer their genetic material across time (Dawkins, 1989); that is, genes are instructions to build bodies that increase the representation of these genes in future generations (termed ‘fitness’) To achieve this end, individuals need to survive and reproduce. Accordingly, our bodies can be understood as a collection of mechanisms or adaptations that are designed to interact with the environment so as to promote survival and reproduction.

In this respect, the human brain is also a collection of adaptations that produce behaviors which enable successful survival and reproduction. For example, feeling hungry is a behavioral adaptation which promotes the representations of the genes that code for it by motivating us to seek food when our bodies (which carry these genes) run out of fuel. The hunger mechanism increases fitness because it enables the organism to survive. Similarly, sexual desire promotes the representations of the genes that code for it by motivating us to seek sexual intercourse. In this case, fitness is increased by the higher number of offspring that result from frequent sexual intercourse.

Still, an individual's genetic material is not only found inside their own body, but also inside the bodies of their relatives. Based on this fact, Hamilton (1964) proposed that evolution favors traits which enable an organism's genes to increase in frequency in future generations, regardless of whether this organism produces offspring directly; that is, an organism can increase the representation of the genes it carries in future generations by helping genetic relatives, such as siblings who carry part of its genetic material, to survive and reproduce. Thus, any gene that predisposed a person to be ‘nice’ to their relatives would have had some chance of benefiting copies of itself inside those relatives, and its copies would have been favored by natural selection. For example, a gene that predisposes an individual to help their nieces and nephews will benefit the copies of itself which are found inside the bodies of those nieces and nephews.

In effect, this disposition indirectly increases fitness by enabling an individual's relatives to survive and reproduce. The sum of direct and indirect fitness effects is called inclusive fitness (Hamilton, 1964). Evolution, then, should have endowed organisms with behavioral mechanisms or adaptations which enable them to maximize their inclusive fitness (Dawkins, 1989).

Trivers (1974) realized that striving to increase one's own inclusive fitness inevitably results in conflict between parents and their children. The reason for this is that the two are not genetically identical: All children's genes come from their parents, but not all of the parents' genes are inside their children. For instance, when parents have a limited resource such as food, they maximize their inclusive fitness by splitting it equally between their children, with whom they share¹ an equal number of genes. However, from the children's point of view, this behavior does not maximize their inclusive fitness because they share only 50% of their genes with their siblings, and so, unavoidably, some of the parents' allocation of resources benefits genes which are not their own. Children, then, prefer to have more than their fair share of parental resources, but their parents prefer to give them only their fair share. As a consequence, the two parties are in conflict over how to split parental resources. In Trivers' formulation, then, parents and children frequently disagree, with the nature of this disagreement being genetic.

Is Parent—Offspring Conflict Possible?

The theory of parent—offspring conflict was criticized by Alexander (1974) as being logically flawed: Any advantage gained by children will be lost when they become parents. To go back to the parental investment example, a gene which enables individuals to get more than their fair share when they are children, at the expense of their parents' total reproductive output, will increase their chances of survival. Nevertheless, they will pay the penalty when they become parents themselves, as their own children will tend to inherit the same gene and will therefore also take more than their fair share of resources. Thus, any advantage gained by children is lost when they become parents (Alexander, 1974). For this reason it is immaterial to talk about parent—offspring conflict as individuals are potentially both children and parents at different times in their life.

The error of Alexander's argument becomes apparent when the perspective moves from that of the individual to that of the gene (Dawkins, 1989; Godfray, 1995). In each generation competition occurs between conflicting alleles (e.g., a disposition to prefer more than the fair share of parental investment) and non-conflicting alleles (e.g., a disposition to prefer only the fair share of parental investment) at the same locus; the conflictor prevails because in each generation the individuals who carry it tend to obtain more advantages (Dawkins, 1989; Godfray, 1995). In Dawkins' words:

Genes in juvenile bodies will be selected for their ability to outsmart parental bodies; genes in parental bodies will be selected for their ability to outsmart the young. There is no paradox in the fact that the very same genes successively occupy a juvenile body and a parental body.

(1989, p. 137)

Accordingly, parent—offspring conflict over mating makes sense when it is viewed from the perspective of the gene rather than that of the individual. In a later publication Alexander (1979, p. 39) acknowledged that his original argument was erroneous.

In-Law Versus Mate Preferences

The Evolution of Mate Preferences

The logic of parent—offspring conflict also applies to mate choice: Children prefer to mate with individuals who maximize their own inclusive fitness and not the inclusive fitness of their parents. This is not going to find agreement with the latter, who prefer to have in-laws who maximize their own inclusive fitness. In effect, there should be a divergence between in-law and mate preferences in respect of traits that give unequal benefits to parents and their children. Before I discuss preferences divergence, however, it would be fruitful to first examine what a preference is.

Let me start by making the assumption that individuals have a blank slate type of mind (i.e., they do not have any innate preferences) and their cognitive functions do not actively engage in mating decisions. As a consequence, mate choice is random. For instance, a man is as likely to choose to mate with a woman who is 20 years old as with a woman who is 60 years old. Now let us assume that a genetic mutation—say, a mutated version of a single gene—predisposes the man who carries it to prefer younger women to older women. What will happen to this gene? The answer is that it will spread rapidly in the population because those who have it gain a selective advantage over those who do not.

The reason for this is that those with the mutated version will divert their limited resources toward attracting young—and thus fertile—women and, as a result, they are likely to have many children who also carry copies of this gene. On the other hand, those who do not have this gene, and thus do not have the preference for youth, are as likely to attract young and fertile women as to attract older and infertile ones and will, therefore, end up having a lower level of reproductive success. Consequently, in the second generation, there are going to be more men who carry the youth-preference gene, who, in turn, are likely to have more children than those who do not have it. This process will continue until those who have the gene replace those who do not in the population.

A similar process takes place for other traits that have fitness consequences, with the end result being a population of individuals who are equipped with well-defined preferences which enable them to find the most beneficial mates. In this respect, mate preferences constitute innate predispositions that have evolved to solve problems associated with mate choice. Of course, the expressed preferences are not solely the outcome of innate predispositions, as higher order cognitive functions also play a significant role (this will be discussed in detail in Chapter 8).

To summarize, evolutionary logic mandates that our minds are equipped with specific preferences that enable us to solve the problem of finding the optimal mate. This logic further mandates that these preferences are contingent upon the sex of the mate-seeker. In particular, because men and women are biologically different, the traits that determine an ideal wife are not the same as the traits that determine an ideal husband. For instance, there is a strong negative relationship between age and fertility for sexually mature women. Therefore, it is beneficial for men to evolve to prefer women who are young. However, this relationship is much weaker for men, for whom there is a strong positive relationship between age and control of resources—i.e., older men control more resources than younger ones. For women, then, the optimal solution is to prefer older rather than younger men (Symons, 1979). As a result, men and women differ in what they prefer in a spouse.

The evolutionary framework, by making specific predictions, has triggered considerable research on mate preferences. The most extensive work in the area has been completed by David Buss and his colleagues. In particular, he and an extensive team of international collaborators asked participants in 37 countries to rate a set of traits in a prospective mate (Buss et al., 1990). They found that people placed traits such as mutual attraction/love, good health, and dependable character high in their hierarchy of preferences. In the middle of their preferences hierarchy were traits such as sociability, ambition/industriousness, and good looks. Finally, they placed traits such as chastity and similar religious background at the bottom of their hierarchy of mate preferences.

Traits were not rated the same in a man as in a woman. In particular, qualities such as ambition/industriousness, good financial prospects, and good earning capacity were valued more highly in a man than in a woman, while traits such as good looks and chastity were valued more highly in a woman than in a man (Buss, 1989). Substantial research has been conducted on exploring mate preferences, and the interested reader should consult David Buss's excellent book The Evolution of Desire.

Overall, evolution has endowed individuals with preferences that enable them to find optimal mates. Still, as I will explain below, the theory of parent—offspring conflict mandates that the optimal mates for children are not the optimal in-laws for their parents. In turn, this indicates that the preferences of parents differ from the respective preferences of their children (see Chapter 8 for a more detailed discussion of the evolution of in-law preferences). The specific areas of divergence between in-law and mate preferences will be discussed next.

Disagreement Over Beauty

Based on the evolutionary perspective, I hypothesized that one area of parent—offspring disagreement over mating is that of genetic quality (Apostolou, 2007a). More specifically, we are a sexually reproducing species, which means that in order to produce viable offspring we need to share our genes with the genes of mates of the opposite sex. As the fate of one's genes depends upon the quality of the mate's or the in-law's genes, individuals should have evolved to prefer spouses and in-laws of good genetic quality because this trait enables the building of strong, healthy and attractive bodies that can deal effectively with the challenges of survival and reproduction.

Accordingly, a gene that predisposes an individual to select a spouse or an in-law of good genetic quality is positively selected because it enables copies of itself to be found in bodies that have a good chance of surviving and reproducing. These copies enjoy an increased probability of representation in future generations relative to competing alleles that are neutral toward good genetic quality. Therefore, good genetic quality is beneficial both in a spouse and in an in-law. The crucial point, however, is that it is more beneficial in the former than in the latter.

In order to better understand the reason for this asymmetry, we need to employ the degree of genetic relatedness (r), which measures the probability that any two individuals share the same gene because they inherited it from the same common ancestor. In this respect, as individuals share half of their genetic material with their children (r = .5), a gene that predisposes an individual to prefer a spouse of good genetic quality is selected because there is a 50% chance that it will find itself in a body which has good chances of survival and reproduction. Similarly, as individuals share a quarter of their genetic material with their grandchildren (r = .25), a gene that predisposes an individual to prefer an in-law of good genetic quality is selected because there is a 25% chance that it will find itself in a body which has good chances of survival and reproduction. Thus, from a gene's perspective, good genetic quality is more beneficial in a spouse than in an in-law, which means that different evolutionary pressures are exercised upon in-law preferences and mate preferences.

In particular, evolutionary forces working on individuals when they act as mate-seekers positively select genes that predispose them to attach considerable weight to the good genetic quality of a prospective mate. Nevertheless, because the benefit is half as much when good genetic quality is found in an in-law, the optimal weight attached to this preference is lower. Hence, evolutionary forces operating upon individuals when they act as parents will positively select genes that ascribe less weight to the genetic quality of a prospective in-law. As a result, there should be a divergence in preferences between parents and their children over genetic quality, with this trait being valued mor...