Evolution and Culture: Parent Preferences: Sons or Daughters?

There are a number of societies in which a parent preference for sons has, on the whole led, to a large discrepancy in the male and female populations. Infanticide, neglect, or, more recently, abortion were the means of expressing this male preference. It was once easy to conclude that this was merely the result of peculiar cultural practices that had developed in a particular region. Sarah Blaffer Hrdy, in her book: Mother Nature: Maternal Instincts and How They Shape the Human Species, tells us that the situation is actually much more complicated, and deeply associated with fundamental biological imperatives.

The fundamental principle of motherhood is to produce offspring that will survive long enough to themselves reproduce. This is an inevitable result of natural selection. The major determinants of survivability are resource availability, and security. A mother can adjust both the number and sex of offspring in response to her perceived expectations for survivability. Lack of resources will convince mothers to limit the number of offspring by either smaller broods or by killing or abandoning the excess. Many animals have been observed to alter the sexual content of the brood produced depending on the prospects of survival. Experiments have determined that for some species there exist innate mechanisms that provide this degree of control. Humans seem to behave similarly in response to the same concerns about survivability, but they await the birth of the child before decisions are made about the viability of the infant.

In species that live in organized societies there are also social or cultural effects in play as well as resource availability.

In societies where resources are limited and rank is acquired from the female, species such as baboons, high ranking mothers will prefer to produce more females because females will benefit most from their mother’s rank. Conversely, lower ranking females will produce more males because males are more likely to survive the disadvantages of low rank and successfully breed than females. If the same species exist in a resource-rich environment, then the population will grow faster, the breeding limitations imposed by rank are less restrictive, and the sexual preference for infants can switch. A high ranked mother can decide that it is more advantages to produce males because males have a greater capacity for reproduction given that they are capable of inseminating many females and more females are now available.

In humans, the fact that males have evolve to be bigger and stronger than females due to the physical competition over mate selection, has generally produced a survival bonus associated with their sex. This was not always necessarily the case. Studies of the earliest hunter-gatherer societies available for observation indicate a wide variety of social arrangements. Nevertheless, as societies evolved to more sedentary structures and domesticated agriculture produced goods and properties that constituted wealth that had to be preserved, patriarchal structures became more dominant. Males were more capable of the critical role of protecting wealth from predators. Male dominance, however, does not necessarily lead to female infanticide. There was a need for a son to carry on the family name and family wealth, but here were many variations on how to deal with other infants.

There are certain preconditions that seem to be necessary for societies such as in India to develop extreme gendercide practices. It is the fragility of the economic health of the society that creates such a social response.

"In a world fraught with economic peril, recurring droughts, famines, and warfare, the best hope for long-term persistence of a lineage was concentration of resources in a strong, well-situated male heir with several wives or concubines. If family circumstances make this tactic doubtful, a daughter or two provide insurance against total extinction of the family line. If a family is truly wretched, the best it can hope for is that daughters will be able to, as slaves, wives or concubines, move up the social scale into positions where their children might possibly survive."

This human behavior is predicted by a hypothesis produced by Robert Trivers and Dan Willard to describe animal behavior.

"Trivers and Willard proposed that parents in good condition should prefer sons, those that were disadvantaged, daughters. They even specified that this logic would be found in socially stratified human societies, where women marry up the social scale, whenever the ‘reproductive success of a male at the upper end of the scale exceeds his sister’s, while that of a female at the lower end of the scale exceeds her brother’s. A tendency for the female to marry a male whose socioeconomic status is higher than hers, will, other things being equal, tend to bring about such a correlation’."

Note that this social construct renders females born at the top of the social structure useless, and males born at the bottom relatively useless.

"Eliminating daughters at the top of the hierarchy produces a vacuum sucking up marriageable girls from below, and creating a shortage at the bottom. Families don’t pay dowries to place daughters in the same or lower status than their own. They demand payment for them instead. At the bottom of the heap, sons whose families cannot cough up the required brideprice remain celibate. Far from calamities, daughters are the most valuable commodities low-status families possess."

Hrdy emphasizes that such societies are not the result of some genetic imperative, but merely a response to a particular environment, one that can change as the environment changes.

"In nineteenth century Rajasthan, where periodic droughts and famines were a certainty, survival of family lines required extreme measures. Heartless? Definitely. And ruthless. But prevailing rules for deciding which sex offspring will contribute most to family ends were devised over generations. Outcomes of successive trial and error, observation of the trial of others, imitation of those who succeed—these became codified as preferences for particular family systems. Adaptive solutions were retained as custom because families that followed these rules survived and prospered."

India is a tremendously diverse country and the incidence of direct or indirect infanticide varies considerably from one region to the other. India was the focus here because it has been the subject of most research. In terms of the ratio of male to female children produced it, as a whole, is far from being the worst offender.

Modernization is changing the ruthless calculus that created the practice of gendercide, but changing a culture is a complex process. As India and China become wealthier, one would expect the practice to die away—gradually.  That has yet to occur on a broad scale.

There is one exceedingly positive data point provided by South Korea. Twenty years ago that country had one of the highest ratios of male children to female children in the world. With the dramatic economic and educational improvements that have occurred throughout the nation in the interim, that country now produces children at near the nominal male to female ratio of about 1.05. An article in The Economist provides this data:

Humans are animals, but they are animals capable of controlling their environment. Better environments produce better behaviors.