An unkind note on sociobiology or evolutionary psychology

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After having argued for the crucial importance of social learning for the stimulus control of sexual behavior as well as for the motor patterns displayed during its execution, I will now briefly turn to the opposite point of view. Some scientists maintain that at least some sexual incentives are unconditioned, while other scientists seem to mean that most of them are so. With an unconditioned stimulus is, as mentioned many times already, understood a stimulus to which humans have an innate tendency to react in a predetermined way. This innate tendency was called an instinct until the concept came into bad repute many years ago. As we know, the main reason for the decline of the concept was that it does not explain anything at all in a satisfactory way. The postulation of an instinct typically answers the question 'why?' and, as we have seen, this question is no longer a part of science. When an animal or a human did something we could not easily explain and someone asked the question 'why did she react in that way?', the answer 'because of an instinct' seemed almost perfect, except for the fact it did not contain any useful information.

When the concept of instinct had spent a sufficiently long time in oblivion for a new generation to be unaware of its disrepute, an equivalent concept appeared. If someone still persisted in asking 'why did she react in that way?' the contemporary answer would be 'evolution has determined that she should do so because it is adaptive'. As was the case with the instinct explanation, the explanation in terms of evolution does not contain any useful information. However, just as was the case with the instincts, the explanation can never be refuted and it appears convincing to some. A meaningless answer to a meaningless question is perhaps always convincing. The revival of the notion of instinct under the cover name of sociobiology or evolutionary psychology has prompted some speculations concerning innate sexual incentives in the form of particular visual stimuli. Within the tradition of beliefs in innate reactions to some external stimuli we also find the hypotheses concerning sexual incentive properties of some chemicals, a subject already discussed and dismissed. Although I keep any idea of innate reaction tendencies as explanations for human behavior in low esteem, I feel obliged to make some mention of such ideas for the sake of completeness of the analysis of sexual incentives in the human.

In 1964, Hamilton proposed an explanation for the strange fact that most females in some species of hymenoptera (an order of insects including bees and ants, among others) are sterile and grant their entire life to the task of caring for their sisters (Hamilton, 1964a, 1964b). This apparently inadaptive behavior had always been explained as caused by some notion of 'good for the species'. This rather primitive teleology did not satisfy biologists and, when Hamilton brought the attention to the fact that the ants had more genes in common with their sisters than with their mother, and that caring for their sisters was a better way to assure survival of their own genes than having progeny, he solved a quite challenging problem. Another ant expert got the idea that if a principle of evolution, inclusive fitness, could convincingly explain an apparently incomprehensible aspect of ant behavior, then it should also be able to explain mysterious features of human behavior (Wilson, 1975). Indeed, Wilson launched a series of explanations of human behaviors inspired by the Darwinian theory of evolution. Other sociobiol-ogists focused their attention on aggression, sex, parental investment and male and female reproductive strategies (e.g. Trivers, 1972; see also Ruse, 1979, for a discussion). This latter focus has become particularly evident in the branch called evolutionary psychology (Buss, 2004, 2005).

Some of the central proposals in evolutionary psychology may be quite entertaining, as long as not taken seriously. Evolutionary psychologists suggest, for example, that since men make a modest investment in reproduction (a short copulation) compared to that of women (at least 9 months of pregnancy and some period of maternal care), it is most reasonable for a woman to take care of her child, while for a man it is more adaptive to impregnate as many women as possible. He will not care for the children anyway. Thus, a well-adapted woman should be a faithful housewife, caring for her children, while an equally well-adapted man should spend his time pursuing other women with the intention of having sex with them. Furthermore, he should not pursue just any woman, but preferably beautiful, young and healthy girls. Such women assure maximum health to their offspring and thereby maximize the probability of survival of the man's genes. Since the behavior patterns described above are the most adaptive, those individuals displaying them deposit more genes in the population than those not displaying them and, after a sufficient number of generations, those genes have become common to the entire humankind. Thus, all women are faithful housewives and all men are rotten bastards not because they want to be, but because evolution has decided that it is the way it must be.

By some peculiar coincidence, the behaviors that evolution has found most adaptive correspond to the stereotypes of womanly and manly that are, at least tacitly, dominant among the American white, protestant middleclass (see e.g. Garcia, 1983; Sprecher et al., 1987; Gagnon and Simon, 2002, for a discussion of social prejudice or stereotypes). There is no reason to make a sociological or cultural analysis of this fact here. This is a task for social scientists. Nevertheless, it may be convenient to remember that explanations in terms of final cause or purpose, teleological explanations, such as those behind the sex differences mentioned above, are always arbitrary. There exists a myriad of possible answers to the questions of 'why?' and 'what for?' are men more promiscuous than women. The answer we choose is inevitably determined by our personal beliefs. If we believe that male promiscuity indeed is adaptive, we can always create an evolutionary argument for that. Evolutionary arguments are, anyway, untestable, so we do not risk much. We may even invent an algorithm and perform complex calculations showing that the argument works. On the contrary, if we believe that male promiscuity is a result of social learning, we can find excellent arguments for that, and perhaps also some supporting data. The reason for the ease of finding multiple and contradictory explanations is that the initial question is meaningless. 'Why?' and 'what for?' have no place in science. It would be far more useful to find out how sexual motivation and copulation are activated, which constraints society has imposed on their expression, and so on. Then, if someone finds sex differences in promiscuity worth studying, men and women could be compared on relevant variables.

Sociobiology, under the name of evolutionary psychology, has become a frequent topic in popular magazines and in some psychology courses. This unfortunate state of affairs obliges me to dwell on the subject a little more. In addition to the criticisms of the analysis of alleged male promiscuity versus female purity already made, I will mention another popular notion in sociobiology that is equally entertaining and equally illustrative of the role of social stereotypes: the ideal of female beauty or attractiveness. The most attractive female body has a waist to hip ratio of 0.70 (Singh, 1993) according to sociobiology. The body shape associated with that ratio is assumed to be indicative of good health, which in turn is a result of good genes. The crucial importance of that figure for female attractiveness has been confirmed in a couple of empirical studies (e.g. Furnham et al., 1998).

The obvious question is whether a waist to hip ratio of 0.70 is attractive because of evolutionary mechanisms or because of social stereotypes. An examination of one of the most important American periodicals, Playboy, could perhaps shed some light on this issue. The young ladies who expose themselves in that publication with an impressive monthly regularity frequently have a waist to hip ratio of 0.70. It has not changed between 1978 and 1998 according to one study (Katzmarzyk and Davis, 2001) and not between 1953 and 2003 according to another (Seifert, 2005). This latter study has also quantified the girls' bust to hip ratio during the same period, without finding any change. Interestingly, although basic body shape had not evolved there was a tendency for the playmates to be more slender in recent years. Slightly different results were obtained from another study of the same photos (Voracek and Fisher, 2002). Body mass index and bust to hip ratio decreased while waist to hip as well as waist to bust ratio increased. The conclusion was that the playmates body mass index has descended below corresponding population levels, whereas the waist to hip ratio has changed in the opposite direction, approaching population levels.

The studies mentioned so far have limited themselves to an analysis of the girls' body shapes without placing them in any wider social context. A different approach to the physical characteristics of playmates has been taken in social psychology. Here, an effort was made to relate the body shape of the Playmate of the Year to social and economic factors that same year. Among the factors included were unemployment rate, disposable personal income, consumer price index, birth rate and marriage rate. It turned out that Playmates of the Year in difficult years were older and taller and had a larger waist to hip ratio than those selected in good years (Pettijohn and Jungeberg, 2004). This might suggest that the ideals of beauty are influenced by socioeconomic factors rather than evolutionary pressures.

There may be many explanations for the real or imaginary changes in Playboy girls' appearance from the 1950s to the 2000s. Perhaps Hugh Hefner's choice of playmates has always been determined by changing evolutionary pressures of which he himself probably is unaware. Another alternative is that he and his staff have a sense of what sells, an intuitive knowledge of social stereotypes and their evolution over time. Whatever the answer to that question may be, Hugh Hefner should be quite flattered by the attention his magazine has attracted from so many scientists. Please note that I have only cited a fraction of the many studies of Playboy's centerfold girls. While reading some of those papers, I almost started to consider the possibility of covering the walls of my office with the kind of photographic materials employed in them, for purely scientific purposes. Social stereotypes would associate such pictures with mechanical workshops or the men's section of a luxury public convenience, but by claiming that they are research materials they would nicely fit into any university office.

Playmates and porn stars usually have large breasts, either naturally or with the help of appropriate surgery and plastic materials, and large breasts are more attractive than small ones (Gitter et al., 1983; Singh and Young, 1995; Furnham et al., 1998). Sociobiology, just as the German philosopher Schopenhauer did more than 150 years ago (Schopenhauer, 1844), tells us that it is because large breasts assure abundant food for the infant. Schopenhauer also discussed the role of other characteristics of the female body contributing to its attractiveness, including what we now would call the body mass index. Within sociobiology, the body mass index is an indicator of good genes competing in importance with the waist to hip ratio (Tovee et al., 1999, 2002; Furnham et al., 2005). If nothing else, the similarity between the ideals of beauty or attractiveness put forth by an 19th century philosopher and present day sociobiologists shows that they are firmly rooted in Western culture. Moreover, the fact that Schopenhauer proposed that these characteristics were associated with inclusive fitness, although he did not use that expression, shows that the purported association between physical appearance and favorable qualities is by no means a derivative of evolutionary theory. Darwin's On the origin of species appeared 15 years after Schopenhauer had published Die Welt als Wille und Vorstellung. Social stereotypes or popular beliefs probably exerted a more profound influence than evolutionary theory ever did on the philosopher's thinking. It might also be illuminating to think about the title Schopenhauer gave to the chapter where he analyzes female attractiveness, The Metaphysics of Sexual Life. As a philosopher, he was aware of the fact that his arguments were purely teleologi-cal and he put them into the category where such arguments belong, metaphysics. Not all sociobiologists show this exemplary modesty.

The preceding paragraphs should have made it clear that there is a coincidence between social ideals of beauty or attractiveness and the sociobiological notion of favorable human characteristics that evolution has made us like. This coincidence may have many causes. One is that evolution, in fact, has determined what individuals in Western societies are attracted to. Another is that beauty or attractiveness are socially determined, in other words that social learning determines what we find attractive or beautiful. This is just one more example of the eternal and certainly meaningless question of whether our behavior is determined by our genes or by our environment. There is, as always, abundant evidence for each of these positions, and what each one of us believes is undoubtedly determined by personal inclination rather than by some process of reason. Fortunately, there is no need and no way to answer the question in the way it is posed. It is in itself based on many assumptions about the causation of behavior, and we do not know if any of these assumptions is supported by data or not. One of the basic assumptions behind the idea that evolution has made a certain shape of the female body more attractive than other shapes is that the attractive shape is associated with some biological qualities making that body a better mate than other bodies. With better mate is either understood a mate that can transmit genes carrying resistance to disease and all kinds of favorable characteristics or a mate whose maternal behavior will ensure larger survival of the offspring than other mates would ensure or, in the best of cases, a mate that possesses both qualities at the same time.

If we believe that the quest for reproductive success has determined how the individual with whom we prefer to reproduce should look, we need to make some assumptions:

1 Potential mates must provide reliable signs indicating their degree of fertility and the likelihood that they will produce multiple and healthy offspring.

2 These signs must vary in intensity or quality between and within individuals according to the individual's degree of fertility and likelihood of producing multiple and healthy offspring.

3 Potential mates must provide reliable signs indicating their capacity to assure survival of the offspring, ideally until they reach sexual maturity. These signs must have predictive value since the care of offspring will become of importance days, weeks, months or years after the moment of fertilization, depending on the length of gestation and obligatory maternal care.

4 The signs must function as unconditioned incentives, insofar as they must be able to activate approach behaviors on the part of individuals from the opposite sex, and they must do so without any previous experience with them.

This series of assumptions, or conditions necessary for any choice of mate to be meaningful in the sociobiological sense, has the advantage of being, at least in principle, testable in contrast to the question as it was initially posed: is the attractiveness of a certain body shape socially or genically determined? (I use the adverb genically rather than genetically, since the latter word stems from the noun genetics, the science studying heredity, while we do not refer to this science but to genes.) However, as we soon shall see, although the assumptions are all testable in principle, some are not in practice. In the following discussion, I will use the waist to hip ratio as an example of attractive body shape. Exactly the same arguments that will be mentioned can be applied to any characteristic supposedly attractive, be it large feet, small eyes, prominent nose or a loud voice.

The first assumption is that a waist to hip ratio of 0.70 is associated with larger fertility than other waist to hip ratios. This is absolutely necessary, because if the genes carrying the characteristic of being attracted to that waist to hip ratio are to be established in the population, the men having them must have more offspring than men not having them. That, in turn, means that the women having the best ratio also must have more offspring than other women. This is an empirical question. We could, for example, determine if the Playboy playmates have more children than women depicted at the before side in advertisements of dieting products. Or we could measure the waist and hip in thousands of young women and determine how many children they have 25 years later. However, such fascinating studies would not answer the question. Contemporary women have the habit of using contraceptives, or they may ask their men to do so. Evidently, the women may also use contraceptives because their man has asked them to. The use of contraceptives could easily bias the results. We know that contraceptive use is influenced by education, income, place of residence, racial belonging, and so on.

Many of the factors determining the frequency of use of contraceptives may also affect the waist to hip ratio. One way to avoid the bias would be to forbid the participants in our study to use contraceptives, but such an approach appears slightly unrealistic. In fact, the worldwide use of contraceptives has made impossible an unbiased study comparing the fertility of women with a waist to hip ratio of 0.70 to that of women with larger or smaller waist to hip ratios. A solution to this could be to use historical data from a time before contraceptives were introduced. Many countries have kept excellent birth registers for centuries. The only problem is that these birth registers do not normally include the waist to hip ratio. It is doubtful whether any do it. Perhaps some old photographs could be used for estimating this crucial ratio, but it is uncertain. In former times people had the unex-plainable habit of being dressed when they went to the photographer and on the occasions where photographs were taken, like weddings or birthdays. Clothing makes any estimate of waist to hip ratio uncertain. Fortunately, this problem was not encountered by those using Playboy photographs. It is a tragedy for science that Hugh Hefner's grandfather didn't launch the magazine. In conclusion, there is no easy way and probably no way at all to correlate the fertility of long since dead women with their waist to hip ratio. Since it is also impossible to do it with contemporary women, we are faced with the conclusion that it is not possible directly to verify the hypothesis. Nevertheless, those favoring it have tried to obtain some indirect evidence in its favor, but again, this indirect evidence rests on some assumptions of unknown veracity.

One of these assumptions is that determinations of fertility could be replaced by determinations of health. The reasoning is that good health may be associated with a long and fertile life, thereby offering the opportunity to have many children and to raise them properly. Furthermore, good health must be dependent on good genes, and healthy women must have better genes than unhealthy women, at least according to sociobiological reasoning. The results from studies of the association between indices of health and the waist to hip ratio are mixed (Ho et al., 2003; Martin et al., 2003; Bigaard et al., 2004) and there is no evidence that a ratio of 0.70 is a reliable indicator of better health than other ratios. When a sociobiological prediction exceptionally is confronted with data, it is not confirmed. After all, why should it be? Social prejudices are rarely based on reality. One example of this appears, in fact, in a study of the waist to hip ratio and incidence of ovarian cancer (Andersson et al., 2004). Whereas the waist to hip ratio was a useless predictor, intense physical activity was associated with an increase in the risk. Social prejudice would have it that intense physical activity is good for your health.

The conclusion must inevitably be that the waist to hip ratio's value as an indicator of fertility is unknown and even impossible to get to know. Approximations, like considering the ratio as an indicator of good health rather than high fertility, have been tested and have failed to confirm the predictive value of it. Consequently, are we forced to conclude that the basic notion of the role of this ratio is not only unfounded but openly false. I could end the discussion of the waist to hip ratio here, since no more arguments are necessary to lay it dead. However, this analysis is not limited to that particular hypothesis, although I systematically use it as an example. We proceed, therefore, with a discussion of assumption number 2 on the list.

Women are fertile only a day or so around the moment of ovulation. There is no reason to believe that the waist to hip ratio substantially or even noticeably changes according to phase of the menstrual cycle. Therefore, it is not a reliable indicator of current fertility. This default can be made less important imagining that women with a convenient waist to hip ratio will form a stable couple with the man attracted to them. For how long have humans formed stable couples? And how stable are they? This last is an important point and it is associated with the question of the predictive value of the waist to hip ratio. Although the ratio does not change during the menstrual cycle, it certainly changes during a lifetime. A favorable ratio at the time a couple is established should predict the fertility of the woman for the entire duration of the couple. If we assume that male-female couples have been long lasting for the last thousands of years and, if we assume that primitive man formed a couple when very young, then the waist to hip ratio at an early age should predict the woman's fertility for a long time ahead. We do not know if this is the case and I cannot imagine any way it could possibly be known with certainty.

The problems caused by the lack of association between the waist to hip ratio and instant fertility can be summarized in the following way: any characteristic needs a long time to become the norm in a species through natural selection. Therefore, we must assume that a waist to hip ratio of 0.70 has been attractive for quite some time. Since it does not vary with instant fertility, its effectiveness must be based on the existence of stable couples. We have, and cannot have, any idea of whether primitive man formed stable couples or not. Furthermore, if stable couples existed for a substantial proportion of the fertile lifetime, the waist to hip ratio must have had predictive validity. This is not known and it cannot become known.

With regard to the potential relationship between waist to hip ratio and the capacity to care for the young we are in a state of ignorance of about the same kind as with regard to the relationship between this ratio and fertility. I do not know of any study showing that mothers' waist to hip ratio of 0.70 is associated with lower infant or child mortality than any other waist to hip ratio. Likewise, I do not know of any study showing that infant or child morbidity is lower in children of women with a waist to hip ratio of 0.70 than in other women. Extensive searches of many databases have failed to illuminate the issue and there is apparently no way to escape from the conclusion that we do not know anything about this.

The last assumption behind the idea that a certain waist to hip ratio is attractive because of some evolutionary mechanism is that its attractiveness does not depend on learning. If it did, then it would be socially and not evolutionary determined. This means that a certain waist to hip ratio must function as an unconditioned sexual incentive. It has never been shown that any waist to hip ratio has unconditioned sexual incentive properties. This excludes, evidently, any possibility for maintaining that a ratio of 0.70 is superior to other ratios. There are few scientists who have speculated about unconditioned sexual incentives in the human. The few that have taken the trouble to do so maintain that there is none (Hardy, 1964; Baldwin and Baldwin, 1997). All sexual incentives are, according to that point of view, conditioned. Mechanical stimulation of the genitalia is intrinsically rewarding and reinforcing, they argue. Any neutral stimulus that is present when genital stimulation occurs can become associated with the pleasure provoked by that stimulation, thereby acquiring the capacity to function as conditioned incentives. The notion of no unconditioned sexual incentive is most parsimonious and scientifically unobjectionable, but most problematic for the hypothesis of a waist to hip ratio of 0.70 as being not only an unconditioned incentive but also superior to other waist to hip ratios.

As we now have seen, none of the basic assumptions behind the idea that a certain waist to hip ratio is attractive because of an evolutionary process is supported by any experimental data. On the contrary, the limited amount of data available indicates that they are unfounded and simple logical reasoning shows that most of them, if not all, are beyond the reach of scientific evaluation. Their justification is entirely teleological and this at a very low level of abstraction.

An explanation of human behavior in terms of purpose or goal is entirely legitimate, since the human may have a representation of the goal and this representation functions as a cause for behavior. In this case, a waist to hip ratio of 0.70 would need to evoke a representation of a child being born and raised to puberty by an able and healthy mother. This representation may in fact exist in the head of a man in some overly romantic movies or best selling novels by Danielle Steele, but it is probably not a major force in most sexual encounters. Nevertheless, it nicely illustrates one of the possible sources of sociobiological teleology: social prejudice, or the conservative middle-class dreams of the ideal life.

Many notions of sociobiology, like the attractiveness of a waist to hip ratio of 0.70, are rather similar to numerous notions of psychoanalysis. Not in content, but in the way that they provide an explanation of the world around us that intuitively makes sense. This, combined with the employment of pseudoscientific arguments and apparent logic, makes such notions very attractive for informed laymen and the popular scientific magazines. It even attracts some behavioral scientists, particularly from the cognitive sciences. They feel probably at home with loose terminology, speculative arguments and sweeping generalizations.

My concern for understanding behavior in terms of cause-effect rather than in terms of hypothetical function as well as a predilection for experiments rather than speculations makes me unfit for appreciating the contributions of sociobiology. To persist in teleological explanations certainly assures continuity from antiquity and on but it can hardly point to the future. Molecular biology has revealed how our genes direct the synthesis of proteins and biochemistry has told us something about what these proteins do. The spectacular progress in these areas is based on experimental studies of cause-effect relationships, not on vain conjectures about final causes.

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