Social sciences are branches of biology
Satoshi Kanazawa, 2004.
3. Puzzles: wage penalty for motherhood, wage reward for fatherhood (and bigger reward from boys than girls)
In a recent study, Budig and England (2001) find that mothers earn less than non-mothers with similar characteristics. The negative effect of motherhood on wage is greater for married mothers than for unmarried mothers. Their finding is in stark contrast to Lundberg and Rose’s (2000) discovery that fathers earn more than non-fathers with similar characteristics. In other words, there appears to be a wage penalty for motherhood and a wage reward for fatherhood.
Both Budig and England (2001) and Lundberg and Rose (2000) use a statistical technique called the fixed-effect model. By using two data points for each individual, before and after parenthood, the fixed-effect model controls for all unobserved heterogeneity, and allows these authors to rule out the possibility of selection bias. In other words, Budig and England (2001) demonstrate that it is not because women with lower earning capacities are more likely to become mothers that mothers earn less than non-mothers, and Lundberg and Rose (2000) demonstrate that it is not because men with higher earning capacities are more likely to become fathers that fathers earn more than non-fathers. It is motherhood itself that reduces wages, and it is fatherhood itself that increases them.
Further, Lundberg and Rose (2002) find, once again using the fixed-effect model, that such ‘wage reward’ for fatherhood is greater if the men have boys than if they have girls. Men earn more, and work longer hours, in response to the birth of sons than to that of daughters. What accounts for these peculiar patterns? What explains the puzzling fact that motherhood carries a wage penalty but fatherhood carries a wage reward, and that such wage reward for fatherhood is greater if the men have sons than if they have daughters?
4. The meaning of life from the evolutionary psychological perspective
Throughout evolutionary history, offspring of men of higher social status and greater political power have had much better chance of survival to sexual maturity, because their fathers could use their status and power to protect them (Betzig, 1986). Women therefore competed to mate with men of higher status and power, and men competed to attain status and power to attract women. Throughout evolutionary history, status and power were men’s means of reproductive success, the ultimate goal of all biological organisms, whereas physically taking care of their children was women’s. In the current environment of capitalist market economy, however, both men’s quest for status and their investment in their offspring often involve material resources (such as money) because status and power often correlate positively with resources. I suggest that this is why men earn more and work longer hours when they become fathers, so that they can invest more in their children and attain greater reproductive success. By the same token, women earn less when they become mothers because accumulating material resources was not their means to reproductive success and women cannot physically take care of the children and earn as much as they did before motherhood, given their time and energy constraints. This is probably why Budig and England’s (2001) analysis shows that married mothers earn less than unmarried mothers. Unlike unmarried mothers, married mothers can depend on their husbands to earn the material resources to invest in their children.
Recall that evolved psychological mechanisms mostly operate beneath and behind conscious thinking. I am not necessarily arguing that this is how men and women think consciously. Whether they are consciously aware of the evolutionary logic behind their desires and preferences is immaterial to EP [Evolutionary Psychology]. I am arguing that men feel like working longer hours and earning more money after they become fathers, and women feel like spending more time taking care of their children. They are not necessarily privy to the evolutionary logic behind their desires and preferences. All the ‘thinking’ has already been done by evolution, so to speak, and it simply ‘equips’ humans with certain desires and preferences. Men and women simply do what they feel like doing or want to do.
[…] Sons’ expected reproductive success depends largely on parents’ wealth, so that sons from wealthy families are expected to attain much greater reproductive success than sons from poor families. This is because sons from wealthy families typically inherit the wealth from their fathers, and can in turn invest the resources in their offspring. Women prefer men with greater resources, and thus wealthy men throughout human evolutionary history have been able to attract a large number of high-quality mates (Betzig, 1986). […]
I suggest that this is why sons produce a greater reward for fatherhood than do daughters. Fathers with sons can increase their reproductive success if they accumulate more resources because they can then pass them on to their sons so that they can attract more mates. Fathers with daughters cannot similarly increase their reproductive success because their daughters’ (and thus their own) reproductive success hinges on factors largely independent of wealth (youth and physical attractiveness). The Trivers-Willard effect also explains why couples with sons are less likely to divorce than couples with only daughters (Morgan, Lye and Condran, 1988; Katzev, Warner and Acock, 1994). Fathers’ parental investment is far more important for sons’ future reproductive success than daughters’. Once again, all of this happens largely unconsciously. Fathers fell like working longer hours and making more money, or staying longer in marriage, when they have a son than when they have a daughter, but they usually don’t know why.
5. What makes us happy ?
If this biological view of humans is correct, then attaining reproductive success should increase our subjective happiness. Throughout evolutionary history, finding a mate has always been a significant adaptive problem for our ancestors (Buss, 1994), and many men, in particular, ended their lives without finding any mate. Once our ancestors found a mate and ‘got married’ (by forming a long-term pair-bond), however, reproductive success (having children) followed as a necessary and immediate consequence of regular mating. In the absence of reliable means of contraception, regular copulation and reproduction in the ancestral environment were essentially the same thing (Kanazawa, 2003), except for the few who were biologically infertile, but we are not descended from them and thus have not inherited their psychological mechanisms.
Evolutionary psychological logic thus predicts that both men and women should be much happier if they are married than if they are not, because marriage (finding and keeping a regular mate) signifies the solution of the most difficult obstacle toward reproductive success. Further, the same logic would predict that, because high social status is an effective means to men’s reproductive success, the accumulation of material resources, which highly correlates with and predicts men’s social status in the capitalist market economy, should increase men’s happiness. In contrast, since social status is not an effective means to women’s reproductive success, the accumulation of material resources should not increase women’s happiness. Men should be far more single-minded in their pursuit of material resources than women are (Browne, 2002). Of course, income and economic welfare are prerequisite for health, which is crucial for motherhood and the subsequent health of the baby. However, in advanced societies like the contemporary United States, from which my data come, virtually everyone, even the poorest person, meets the minimum requirement for physical health and welfare. Very few Americans today have health problems because they are too poor.
Table 1 presents an analysis of data from the General Social Survey (1972-98). I present the empirical data here only for illustrative purposes, not as a rigorous empirical test of competing hypotheses. Because the dependent variable measuring happiness is ordinal (1 = ‘not too happy’, 2 = ‘pretty happy’, 3 = ‘very happy’), I use ordinal regression (McCullagh, 1980). The results in Table 1 show that, controlling for age, race (black = 1), education and survey year, being currently married significantly (ps < 0.001) increases both men’s and women’s happiness. This finding is consistent with earlier reports of the strong positive effect of marriage on happiness (Waite and Lehrer, 2003). The interaction between being currently married and having children is also significant for both men (p < 0.01) and women (p < 0.001), suggesting that being married with children significantly increases the respondent’s happiness.
In addition, the respondent’s income (measured in 12 ordinal categories) significantly (p < 0.001) increases men’s happiness, but it has no effect on women’s happiness. Both of these patterns are consistent with the evolutionary psychological predictions. Incidentally, the strongly significantly (p < 0.001) negative effect of survey year on women’s happiness demonstrates that women have gradually become less and less happy in the United States over the last quarter-century, when men’s happiness has marginally significantly (p < 0.10) increased over the same period.
There is one anomaly in the ordinal regression results presented in Table 1, however. While, consistent with my evolutionary psychological prediction, both being currently married (the main term) and being married with children (the interaction term) have significantly positive effects on happiness, for both men and women, the main term for parenthood has an equally significantly negative effect for both men and women (ps < 0.001). The negative coefficient for the main term for parenthood is highly larger than the positive coefficient for the interaction term for both men and women, suggesting that, whether they are married or not, having children actually reduces the respondents’ absolute levels of happiness. How could this be? If, as I argue, the ultimate goal of all biological organisms is reproductive success, and if emotions are designed to induce organisms to engage in behaviour that helps them achieve this goal, how can individuals with children be less happy than their childless counterparts?
I believe that this anomalous finding may point to the potential limits of EP as an explanation of human behaviour in the current environment. As I note above (in section 2), all evolved psychological mechanisms are adapted to (and thus assume that we still live in) the EEA (Kanazawa, 2002, 2004). To the extent that our current environment is different from the EEA, our evolved psychological mechanisms often malfunction and misfire.
Parents today must raise their children in a radically different environment from the EEA [Environment of Evolutionary Adaptadness]. They must drive them to and from daycare centres and soccer practices, they must put them through compulsory school and pay for their higher education, they must feed, clothe and shelter them in their adolescence and early adulthood (when they would have been economically independent in the EEA soon after puberty), they must purchase computers, cars and other expensive gadgets for them, etc. The list is endless. I suspect that having to raise children in an evolutionarily novel environment might suspend the operation of evolved psychological mechanisms (and the preferences, desires and emotions they engender) and allow other mechanisms to kick in and influence their happiness. Economic and sociological theories are indispensable in explaining these other mechanisms that might overtake and supersede evolved psychological mechanisms in the current environment.
For instance, Becker (1991, pp. 135-78) presents a microeconomic model of the demand for children which not only provides alternative explanations for phenomena that EP can also explain, such as why mothers spend more time and effort taking care of their children than fathers do (see above), but can also explain phenomena for which, to my knowledge, EP has not been able to provide satisfactory explanations, such as why rural fertility is typically higher than urban fertility or why there has been a steady decline in fertility throughout the world in the last couple of centuries. (In fact, what the demographers call the ‘demographic transition’ and the current apparent equilibrium on the two-child family are two of the great mysteries to EP.) Becker’s microeconomic model can offer satisfactory explanations to these phenomena from a rational-choice, cost-benefit perspective, with only four independent variables: price, income, demand and supply.
Given all of this, and in the current state of development of EP, it is difficult to refute Becker’s contention that ‘To be sure, the Darwinian theory is highly relevant to nonhuman species and, modified to include cultural selection, may also be relevant to some primitive human societies … However, the analysis developed here is far more suited to explaining fertility changes in Western countries during the last few centuries and in developing countries during this century’ (Becker, 1991, p. 137). What Becker is unwittingly yet very presciently pointing to may be the distinction between the EEA and the current environment.
Of course, Becker himself is an unabashed reductionist like me, and thus socioeconomists who are critical of reductionism may have other objections to or concerns with my call to subsume social sciences under evolutionary biology and psychology. In particular, such critics may point to the inherent difficulty in figuring out precisely what the EEA was like, tens and hundreds of thousands of years before the present, and what its implications are for human behaviour today.
Analyse Economique 