According to neo-Darwinian synthesis, evolutionary success is defined largely in terms of fecundity, or reproductive success, not just survival. It is the replication of the gene that matters most, not the organism. If reproductive success through genetic replication is the ultimate goal of evolution, then resource acquisition can be seen as merely a means to an end.

A great deal  of contemporary work on human social behavior, including religiosity, employs the “social evolution” framework outlined above. Of course genetic replication in human occurs through sexual reproduction and so significant features of human minds evolved, presumably for the purpose of attracting and securing mates.

Humans are heterogamous, meaning that genetic replication occurs with the fusion of two dissimilar gametes (sex cells). In heterogamous species like ours, females have larger gametes than males; indeed, this is what defines “femaleness”in biology. The average ovum in a human female is 150 µm while the average sperm is 2-3 µm wide and 5-7 µm long. With such relatively large gametes, females can only produce and store a finite number of eggs. On average, even though many more are present at birth, a female has 400 reproductive opportunities for genetic replication in a lifetime. In contrast, estimates are that the average human male produces over 500 bollion sperm in a lifetime, and can release between forty million and one billion sperm in a single ejaculation. So males can produce hundreds if not thousands of offspring in a lifetime, assuming they are able to convince a female to mate. And this is the key insight for understanding human behaviour. Since sperm are “cheap” and eggs are “expensive”, females choose and males woo.

In addition to the significant difference in reproductive opportunities between males and females, there are significant differences in reproductive costs. Women bare all of the biological burdens of gestation, birth and nursing, while males have little necessary direct parental investment. Should they choose to do so, in fact, soon after reproducing with one female, male could continue to reproduce with other females. In contrast, once pregnant, a female cannot reproduce until months later. Thus the record for the most children sired by a female is purported to be sixty-nine, sixty seven of whom survived infancy. In contrast, Mulai Ismail, the last Sharifian Empror of Moracco, is believed to have sired over 1,000 children.

Given thse biological realities, males and females employ different behavioural strategies. In general, females are choosier than men because the costs of reproduction are so high (there are only a few opportunities in a woman’s lifetime). What follows is an evolutionary “arms race”: inter-sexual competition, driven by female choice. Women want certain qualities in a mate, and men engage in behavioural displays which signal that they possess those desirable traits. Women in turn must judge whether the male’s displays are honest or deceitful. In other words, women know what they want, men claim to have it and women have to figure out if they are telling the truth. This is the evolutionary arms race between the sexes.

Moreover, human mating psychology is equipped for intra-sexual competition. Males compete with males for access to females, and females compete with females for access to desirable males. Given that female choice is central for heterogametic reproduction, intra-sexual competition is fiercest among males, which is why in most heterogamous species males have larger and more ornate displays. Growing large physical displays, such as a peacock’s tail, or engaging in costly behaviours, such as birdsong or bower building, is a strategy to handicap rivals. Only males with the highest quality genes can afford the costs of large plumage or risky behaviours, and costly displays are hard-to-fake signals of genetic quality.

These facts of evolutionary biology may ultimately explain all of human behaviour. Indeed, if genetic replication is the sole goal for which all organisms are designed, everything else is a means to that end, religiosity included. Religiosity may be a reproductive strategy. New research indeed suggests that it is.

Many contemporary scholars have put forth evolutionary explanations of religiosity based on the logic of sexual selection theory. The theory, in short, is that religiosity is display behaviour designed to solve adaptive problems relating to mating and reproduction. For example, a research found the stronger predictors of attending church were those related to sexual and family values, and thus attitudes about sex and family are causes, not effects, of religious attendance. Further, in an exprimental studies, people reported higher religiosity after looking at mating pools consisting of attractive people of their own sex compared with attractive opposite sex targets, suggesting that both men and women become more religious when seeing same sex competitors.

Conclusion: Marx was wrong when he claimed that “religion is the opium of masses.” The answer is this: low-status individuals might not be using religion as an opium for escape, but rather as an aphrodisiac for attraction.
Source: Jason Slone, The opium or the aphrodisiac of the people? Darwinizing Marx on religion.,in Mental Culture, edited by: Dimitris Xygalatas and William W. Mc Corkle Jr.