Sunday, May 9, 2010

Are Humans Essentially Monogamous?

This is an essay from a uni subject I did, just an interesting topic.

In humans, a monogamous relationship is the pairing of two humans who will frequently mate exclusively with one another. However, the human idea of monogamy is that they should only mate with one another. In regards to this paper, the definition of monogamy as exclusively mating with one partner will be taken. Polygamy will be defined as taking multiple partners, though these partners are not always aware that they are sharing their mate. There are evolutionary, biological, genetic and social aspects to consider when dealing with the subject of human interaction and mating.

There is a strong argument in favour of monogamy in humans from both biological and social perspectives. There is a key factor that most scientists in the field agree upon, paternal investment that ensures survival of the offspring. Biparental care appears to be the driving factor of monogamy in humans. By pooling resources, the parents can best provide for their offspring. Simply not having enough land/property to spread between offspring from multiple females can result in a preference to monogamy. As Marlowe (2000) mentions, for every one offspring resources must be delegated. For every other offspring the resources must be portioned out, lessening the amount for each. This is also inclusive of potential offspring, causing costs of parental care to outweigh benefits of mating polygamously. There is also the possibility that the more exclusive the care/provisioning for the female’s offspring, the greater the degree of fidelity the females award males (Marlowe 2000, Fortunato & Archetti 2009).

Ownership of various material objects can relate to the modern idea of fitness. Infidelity in most western cultures is considered grounds for divorce in married couples and the perpetrator tends to be worse off in legal terms. In such an instance there could be, given that resources are an all important factor in mate attraction, that once the cheating mate has been stripped of most of his/her resources that they will no longer be as desirable to other potential mates (Drigotas & Barta, 2001). This is particularly true for females who are divorced and retain children from their previous partner (Marlowe 2000,).

Parental care from males can be delivered both directly and indirectly. The male can care directly for the offspring or he can aid the mother which allows her to care for the child (Quinlan, 2008). Fortunato & Archetti (2009) postulate that the evolution of monogamous relationships was a result of the insufficient skill of males to mate polygamously. The fittest males may have monopolised the females, preventing the lesser specimens from attaining a mate. Therefore, it is entirely possible that when the less fit males were able to mate, this resulted in mate guarding against the fitter males (Fortunato & Archetti 2009, Marlowe 2000).

There are many theories surrounding monogamy and pair-bonding. Pair-bonding is when a couple form an essentially monogamous relationship and prefer the company of one another to that of strangers (Curtis et al, 2006). There are many theories as to how monogamy evolved. Pair-bond formation between humans may be a result of several factors. A possible reason for pair-bond formation is provisioning for offspring and in particular, of females during the breast feeding stage of child rearing. It is during this period that the mother required sustenance with which to feed and care for the child. Due to the intense degree of time and care required for the child, the mother cannot provision for herself let along for the child (Quinlan, 2008).

A pertinent question may be, when the offspring are weaned and are not constantly reliant on the mother, what use is there for the male to remain? In humans, child rearing is a long and expensive endeavour which is why both parents are required to remain and contribute resources to the offspring until it is able to acquire resources itself. However, frequently these long term pair-bonds tend to be formed out of willingness and happiness as opposed to obligation or necessity. If/when we as humans are not able to forge such bonds it is often seen as a sign of mental perturbation or psychoses (Curtis et al, 2006). Why do we form deep emotional bonds to people if the monogamy is based purely on provision for offspring? How, if at all, are pair-bonds dependant on these emotions? There is evidence to suggest that pair-bonding is neurologically based.

There has been strong evidence from recent studies to suggest that neurochemicals play a central role in forming pair-bonds. Referring to a study done on mice by Ribble (1992), it showed that remaining with the same partner leads to greater reproductive success in their lifetime. This may have been a contributing factor to the evolution of monogamy and the related theory of pair-bonding. These animals naturally form pair-bonds and exhibit a preference to associate with their partner than a stranger. Dopamine is a neurotransmitter that has been shown to affect social interactions in these voles but also in humans. A particular species of vole tends to display a similar behaviour to human pair-bonding which makes them ideal for an experiment to test dopamine’s effect on said behaviour. The study showed that when a dopamine antagonist, haloperidol, was administered, pair-bonding in the voles was impaired (Curtis et al 2006). A separate study, again using voles, by Young and Wang (2004) showed that when the females were treated with oxytocin, a neuropeptide, the exhibited accelerated the pair-bonding behaviour, that is they formed a partner preference in a short time of cohabitation without mating. This study also tested the effect of arginine vassopressin, another neuropeptide, in males showed a similar response as oxytocin did in females. These studies have very strong implications that monogamy in humans, as we too have these neuropeptides, may be largely a result of neurological programming.

Mate guarding is an example of where the line between the social and the biological reasons for monogamy blurs. Mate guarding by males, usually construed as jealousy in humans, is a method of ensuring his partner only mates with him, therefore reduces extra-pair paternity. Thus any resulting offspring have a larger probability of being his (Shackelford et al, 2006). If we consider the social reasons for the evolution of human monogamy we find that they are slightly incongruent with the more biologically based reasoning. Mate guarding, generally considered a useful tool in preventing extra-pair copulation in partners has a social downside. Due to the severity of mate guarding there would be a large degree of hostility toward other males in social groups. Humans have learned that cooperation is most often times better than constant competition, this same principle may also be applied to mating. There is a definite advantage for groups that strengthen via cooperation. If there is a reduction of in-group competition, cooperation would increase, forming a stronger community. Thus giving those groups a survival advantage over those that struggle through in-fighting (Fortunato & Archetti, 2009). The human “wing-man” is a possible example of this. In contemporary society in western culture the “wing-man” is the male companion of another male who aids in mate attraction. It is the cooperation between males wherein one, the wing-man, will sabotage his own chances of mating while simultaneously making his companion appear more appealing to the female (Grazian, 2007). This is an excellent example of human altruism.

Of course one of the largest social promoters for monogamy lies in religion, most notably Christianity. Christianity is a religion that socially imposed monogamy on the medieval societies of 11th century Western Europe that has carried well into the 21st century and farther reaching corners of the globe (MacDonald, 1995). In large societies where Christianity is the dominant religion and is actively being practiced monogamy would be the prevailing form of mating behaviour.

There are myriad reasons why monogamy is not a favourable practice for humans to adopt. In the first instance, it is more beneficial for males to be polygamous. As they invest little in gamete production and are not obligated to the females after fertilization, they ought to spread their genes as much as possible. If females are to invest in reproduction, it would be prudent to mate with the fittest male to ensure healthy offspring. The most desirable polygamous situation for females is that they ought to mate with the male with the best genes and to form a pair-bond with the male who will be the best provider for the offspring as paternity is often uncertain where males are concerned (Seki et al, 2007).

Another reason that polygamy may be preferred amongst humans is that they experience mate dissatisfaction or what is sometimes deemed boredom. They may therefore will seek out another mate, be it for a long or short term pairing. The most likely cause for women to perform extra pair copulation is because they are unhappy with the choice of partner. Whereas males may be perfectly happy with their choice of partner but will still mate with other females. This behaviour is usually based largely on sexual attraction of a third party and is not commonly for long term pairing (Drigotas & Barta, 2001). However, in this era where sex is no longer purely about reproduction, why shouldn’t we reproduce with those that we form pair-bonds with so as to ensure against extra-pair paternity, but continue with extra-pair copulation? Surely if there is no threat of non-paternity there should be no requirement for mate-guarding and therefore no jealousy.

It is theorised by Fortunato & Archetti (2009) that socially imposed monogamy removes male breeding success. By not allowing a genetically superior male or one that will best provide for offspring to proliferate with several females it does not allow females to select a premium mate. Only a single female is socially permitted access to that male for breeding purposes once they have entered a relationship. Those that missed out on this specimen are forced to choose amongst those males that are left, despite their perceived lack of relative fitness. This creates a disadvantage to those females in terms of genetically ideal offspring as well as more competition among them for an adequate mate (Fortunato & Archetti, 2009).

There is a form of polygamy that is more socially acceptable in society serial monogamy. This is a practice wherein the male in the relationship would be most interested in moving from one partner to another and fathering as many children as possible until the female has declined in residual reproductive value. So long as the pair-bond has been broken between the two, the male is free to pursue a younger, more fertile female and repeat the cycle (Marlowe 2000,).

In Scheidel’s (2009) work, sited by Fortunato & Archetti (2009), it brings to light that, though strict monogamous marriages existed in early Rome, there were many males of high status that fathered many children with slave girls, thus compounding the idea that males who tend to view themselves as more resource-rich than or physically superior to other males may have a sense of self entitlement (Drigotas 7 Barta, 2001). A societal development in the mid 20th century, women entering the workforce, has lead to another evolutionary shift away from this paradigm so to speak. The more women could contribute to the resources for child rearing, the less inclined the male was to maintain monogamy. The benefit of monogamy gradually decreases as the female becomes more adept at provisioning (Fortunato & Archetti, 2009). It would seem that there is little point of forming pair-bonds in order to care for the offspring in contemporary society when the females may invest less time and energy into parental care with the aid of day care centres and nannies.

As the Christian faith defends monogamy, Muslims and Mormons are encouraged for males to take multiple wives. Mormons actually do follow the general principal of Marlowe’s (2000) theory of serial monogamy, however they retain the wives that are no longer reproductively valuable.

Despite the genetic and biological benefits of polygamy Humans are essentially monogamous, essentially being the operative word. There is the concept of serial monogamy that it still looked upon as a version of monogamy. This allows for the biological theories of the benefits of polygamy to be maintained as well as the social theories regarding the benefits of monogamy and pair-bonding (Marlowe 2000,). The female who is no longer able to reproduce has already done so and her offspring have been provided for.

The benefits of monogamy and polygamy are contradictory at best. It is better to be polygamous and mate with several partners than it is to be monogamous and limit your genes to the one partner (Fortunato & Archetti, 2009). However, it is better to be monogamous to ensure the survival of these potential offspring. Though there is evidence of pair-bonding and increased lifetime reproductive success eventually the female will reach menopause and this will decrease the male’s lifetime reproductive success as he will not be permitted to access a younger, fertile female with which to mate without incurring possible divorce, however much that is unfavourable to the older female (Marlowe 2000, Ribble 1992). Religious faiths even diverge drastically on this seemingly universal issue.

From a purely biological perspective, it is easy to understand why humans might be predisposed to infidelity. The male with the most reproductive prowess mates with multiple females so his DNA may carry on via several offspring. The females in turn will have mated with the fittest male, ensuring their offspring’s fitness for further proliferation of their DNA. There is an interesting theory that can be gleaned thus far as to why humans may prefer to be polygamous but have those they mate with remain monogamous. Females for instance would like to have both the male that is the best provider and the male with the most beneficial genes, therefore will pair with the caring male and mate with the genetically superior male. Monogamy in males is desired by females so that they know the male is not dividing his resources between other offspring and only providing for her offspring. Males will try to mate with as many females as they can to further their genes. However, as paternity is easily hidden from males, he will be unwilling to provide for his partner’s offspring he isn’t certain are his own (Fortunato & Archetti, 2009). Schuiling (2003) remarks rather adequately; “For humans, the optimal evolutionary strategy is monogamy when necessary, polygamy when possible”.

2 comments:

  1. This is a really long essay I had to write for uni. It might come in handy for anyone who wants to know a little on the subject of human mating.

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  2. Favorite part: "mate dissatisfaction or ... boredom." As much as I science stuff is dense for me I do find it interesting to hear the things nearly every poet, musician, writer has ever talked about in love with so factually terms.

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