Four Observations About Mating

I have been too busy to do much reading recently, so here is something from my Human Nature course.  I offer four observations that lay out one of the general theories of sociobiology. 

Observation 1: Males are larger, stronger, better armed, and more aggressive, across a wide range of species. 

This is not universally true.  Spiders are a conspicuous exception.  There the reproductive machinery resists reduction in size.  Ask a black widow male what he thinks about this.  It is however true of a vast number of species including elk, gorillas, walruses, and human beings.  Why? 

Observation 2: Males compete with other males for reproductive opportunities. 

In most species that I am aware of, almost all of the females can successfully mate.  They may compete with other females for access to the most competitive males, but they get to mate with someone.  By contrast, males will often go without mating opportunities at all.  This is especially true in harem species, where males enjoy access to a considerable number of mates so long as they can defend their position against other males. 

In harem species the sexual dimorphism is rather large.  In promiscuous species, larger males may not enjoy exclusive access but they often enjoy the first opportunity to mate with a fertile female.  In some monkey species, the males compete not with size and offensive weapons like antlers, but with large testes, the better to flush out the work of the last suitor.  In yet another strategy, males compete by features that attract females, such as color or flamboyant tail features. 

In the case of harem species, female choice is limited but not extinguished.  A female may cry out to arouse the dominate male if an interloper appears.  She doesn’t want to mate with the Johnny-come-lately unless he can stand his ground.  Where females can easily flee, female choice is accordingly increased.  Hence the colorful male birds. 

In all such cases, males with weapons leave more offspring than males without or with lower caliber weapons.  Accordingly, they sire sons with the same weapons. 

Observation 3: females are choosy but males are eager. 

Across a wide range of species, males will take any opportunity to mate that they can get, whereas females will resist any suitor that they regard as unsuitable.  While female choice will be more or less constrained depending on the mating system, they will exercise as much choice as possible.  Males will mate with anything that looks vaguely female.  Mount a female turkey’s head at the appropriate level and a male turkey will move behind it and try to mate. 

Observation 4: sperm is cheap; eggs are expensive.  

 The male’s minimal investment in a single reproductive act is often very minimal.  For most males, each mating is chance to sire more offspring.  Hence eagerness to mate is selected for.  For females of many species, the minimal investment in a single reproductive act is very large.  Indeed, the universal definition of female in biology is the sex with the largest sex cell. 

We can see this spread across a number of mating systems.  Where the female lays eggs to be fertilized externally by the male, her investment is relatively small for a female.  However, it is still larger than the males.  In hermaphrodite fish, where each individual produces both eggs and sperm, the eggs are more precious.  This fact results in a social contract called parceling.  When two such fish meet, each lays a parcel of eggs for the other to fertilize and then they repeat the exchange.  A fish that managed to fertilize all the eggs of another without giving up any of its own eggs would be able to cheat many other fish before he/she finally released his/her own cache of eggs. 

Females that develop an egg within their own bodies must devote a lot of time and resources to each reproductive opportunity.  Those that allow the young to develop to live birth must devote even more. 

The result is that the minimal cost of each reproductive act for females is much larger than it is or can be for the male.  More coupling does not result in more offspring.  Accordingly, the female is inclined to make sure that each coupling counts and that means being choosy (when she can) about whom to mate with. 

Thus the four basic observations can be arranged so that each one helps to explain the previous one.  Males are better armed because they compete with other males; they compete because males are choosier than females; males are choosier because their minimal investment is less.  Given Darwinian theory, we can now understand a lot about the sexual behavior of elk and the guys down at the Elks Lodge. 

The Evolution of Marriage

Larry Arnhart discusses the biological roots of marriage in a recent post.  I am sorry to report that I agree with Larry on the basic issues.  I am happy to report some skepticism regarding a secondary issue. 

Larry is responding to Sherif Girgis, Ryan Anderson, and Robert George, who argue that marriage should be restricted to a monogamous, heterosexual relationship.  He tells us that the authors make two points: one, that marriage is an institution rooted in human biology and two, that if homosexual marriage is legalized this will effectively destroy heterosexual marriage. 

Larry agrees with the first point but thinks that it is inconsistent with the second point.  If heterosexual marriage is indeed rooted in nature, then it should survive any changes in legal norms.  I am inclined to agree. 

Allow me to add some of my own reflections.  Marriage is rooted in a simple biological dimorphism: women know who their children are while men do not.  When an infant issues from her mother, the mother knows that the infant is hers.  The father must rely, let us say, on less direct evidence.  How confident can he be that he is the biological father?  This has Darwinian implications, in so far as his natural instincts move him to invest in his offspring. 

The problem is widely shared among animals and has had enormous consequences for their evolution.  Males of many species try to secure paternity by keeping other males away from their mates.  Some jealously guard their harems.  Canines have evolved a mechanism called a “copulatory lock”.  When the male enters the female, his organ expands and locks him in place.  He cannot engage until sometime after ejaculation, which makes it more likely that the female will be safely impregnated.  That is the tie that binds. 

Security for paternity encourages the male to invest his time and other resources in his offspring.  Of course there is a trade-off.  If the male is fooled, he will waste his resources on the offspring of some other male.  Likewise, he will be tempted to hedge his bets by siring offspring with other females, perhaps with false promises of support.  Such is the soap opera of mammalian biology.  If male parental investment is to be maintained against or supported by selection pressure, some means of securing paternity have to be available to the male. 

The human institution of marriage was built on these biological foundations.  Marriage offers the male some assurance of paternity in exchange for his promise of investment.  That contract is reinforced by the larger community, which recognizes his authority over his sons and daughters.  See Aristophanes Clouds.  It also puts a disproportionate weight on the fidelity of the wife. 

However, marriage is not a product of biology even if it rests on biological foundations.  It arises and is maintained because it is one of the conditions for human flourishing in social conditions.  The telos, or purpose of marriage, was not reproductive success in a Darwinian sense.  It was to promote societies that are more stable and satisfying, given our evolved inclinations.  Human institutions cannot for long act against natural selection; however, they exist to serve us and not our genes. 

Given that brief consideration of the biological foundations of marriage, what does it mean to extend the institution to include homosexual couples?  It means only that an institution that has been developed for one purpose has been employed for another.  This is a commonplace in both biological and cultural history.  In the ubiquitous beetles, a second set of wings evolved into a retractable coat of armor.  Clothing likely emerges as a remedy for discomfort in hostile climates; however, it comes to serve other purposes such as displaying wealth and status, inviting seduction, providing pockets, etc. 

While heterosexual marriage evolved to serve purposes connected with biological reproduction and familial stability, there is no reason to suppose that it cannot serve other purposes.  Some have argued that same sex marriage can promote monogamy among male homosexuals, which might well be a good thing.  Whether it can really do that remains to be seen.  I have my doubts.  

I am in favor of legal same sex marriage for a rather simple reason.  When two persons of the same sex form a stable relationship, analogous to heterosexual marriage, the two partners should enjoy the same privileges as a heterosexual couple who have chosen to marry.  When one goes to the hospital, the other should have the same medical access that I and my wife have.  This strikes me as the decent thing to do. 

I see no reason to suppose that this undermines the functions of heterosexual marriage any more than wearing cloths to make a fashion statement undermines the purpose of good winter gear in these Dakotas. 

That said, I am not at all certain that I agree with Larry Arnhart regarding the privatization of marriage.  Such a step would certainly render moot the political arguments over marriage, just as the privatization of religion dramatically reduced the tendencies toward armed conflicts between sects.  However, this step clearly weakened religion as a force in secularized societies.  As I noted above, marriage is an artificial institution and it can be stronger or weaker in its effects, depending on how it is managed. 

I think that marriage is one of the most important institutions in human history.  We want to encourage it and strengthen it, in so far as we can.  I suspect that privatizing it would weaken it by placing in the category of things that are not serious enough to have legal consequences.  Because I agree with Larry that marriage has deep foundations in human biology, I don’t expect that this would kill marriage.  I do think that it might weaken it further.  If I am right, that would be a step in the wrong direction.