Today the goal is to look at a few simple rules that govern all living things (natural selection sexual selection and inclusive fitness. Once we understand those rules, we’ll look at how those rules shape adaptations – adaptations that can be primary, secondary or simply random. Finally, we’ll apply these biological rules to aspects of human culture and cultural norms, especially cultural beliefs that are universal. This process is called “evolutionary psychology”.

The adaptations we carry with us helped us first survive an often hostile environment. But also, some adaptations helped us reproduce more effectively. Both survival and reproduction are needed to ensure the continuation of the human race – survival alone is not enough, reproduction alone is not enough. Both are required. This needed combination is often overlooked – as is also the fact that adaptations that help us survive and reproduce but then carry negative consequences in old age (say, male pattern baldness) would still be passed on.

Natural selection is the main motor behind evolution. As seen in the simple drawing here – some environmental factor kills off low shrubs leaving only tall trees. Animals with short necks now do not carry a successful adaptation – but those animals with long necks do have a successful adaptation. They thrive, the short-necks die and after several generations, a new species of long-necked animals (giraffes) is added to the diversity of life on the planet.

Evolutionary processes are difficult to see because they operate over vast stretches of time – time spans that are truly beyond human comprehension. Humans themselves have used natural selection (well, to be specific – unnatural, human-driven selection) to modify and change plants and animals. Think of how humans gradually developed corn from a native grass called teosinte. Or how both the Chihuahua and the Great Dane come from the same root animal, which resembles a wolf.

Reproduction is the other motor driving the selection process. Adaptations that improve the ability of an organism to mate and reproduce will be passed on to future generations even if those adaptations are working against long-term survival. An adaptation that results in lots of reproductive success but actually lowers life expectancy will still get passed on because at the level of the gene, reproductive success is all that matters. The peacock’s tail is the obvious example, as are giant antlers on the heads of stags.

Adaptations can arise because they make you better at attracting mates (once again, the peacock’s tail) – this is called intersexual competition. Or adaptations can be passed on because they make you better at beating out others for access to mates, which is called intrasexual competition. Here, the best example would be he antlers of the male deer. Human examples of intersexual competition include longer hair for women and female body shape. For intrasexual competition, young men are exceptionally predisposed towards violence, usually towards other young men.

One final driver of evolution is the idea of inclusive fitness. At the genetic level, an adaptation that doesn’t help my reproductive or survival success but does positively impact the survival of my close genetic relatives will get passed on to future generations. Society and culture are possible evolutionary adaptations that occur because they contribute to inclusive fitness.

Not everything is a primary adaptation to a survival or reproduction problem. Some adaptations are by-products of larger ones. We think that hair length on women is a sexually-selected primary adaptation. Whether long female hair is straight or curly is probably an incidental by-product. If the genes that control longer hair in women are also responsible for (say) earlobe shape, then earlobe shape would be a type of incidental “tag-a-long”. We get the incidental by-product to gain the very beneficial primary adaptation.

As mentioned earlier, families and societies can lead to greater inclusive fitness. Humans use culture (a set of shared beliefs or values) to pass on adaptive behaviors from one generation to the next. Cultural universals – behaviors common to all cultures – are excellent candidates to be looked at as adaptive problem solvers. Religion is such a cultural universal. Why is it so common? It does do an excellent job of ensuring cooperation and group cohesion as group sizes get large. There are obviously intergroup conflict potentials – one religious group trying to destroy another – but the intragroup benefits of religion are significant.

As we saw with inclusive fitness, altruism should follow lines of genetic relatedness. I’m more willing to sacrifice myself to save my son than I would be to sacrifice myself to save my second cousin.

Every successful act of adultery requires both a female and a male partner – but do the two sexes have the same tradeoffs? The same rewards? Are they solving the same problems? Male adultery is straightforward – male adulterers are rewarded by seeing the near-limitless spread of their genes through a near-limitless number of potential children. This, by the way, is called an “R” reproductive strategy – have as many offspring as possible, hoping that there is strength in numbers and that a few of them will survive. But women employ “K” strategies – lavish all your resources on a few children to guarantee them the best chance of survival. Why would a woman commit adultery and run the risk of alienating her spouse and losing his support for her children?

Two theories attempt to explain female adultery, each has its own strengths and weaknesses. The Resource Theory says that women cheat so that they can access resources from multiple men. More resources means more survival success for their offspring. A second theory says that female adultery is driven by a desire to engage in mate switching, that adulterous women are “kicking the tires” of potential new mates after their current mate fails to provide.

Here we see mate age preferences for men and women. Women prefer men the same age or a little older while men… well, men prefer young women no matter how old they are. This is solid evidence that women view sex as a way to gain resources for their children (K strategy) while men use sex to maximize their number of potential children (R strategy).

Jealousy also has a sexually differentiated aspect. Studies show that men are far more concerned about sexual infidelity while women care more about deep emotional attachments (an “emotional affair”). This difference would be consistent with the idea that men engage in an R strategy (maximize the number of offspring) while women engage in K strategies (maximize the amount of resources directed at a few children). In patriarchal cultures, where men control the society, institutions and customs are in place to prohibit sexual infidelity, up to and including truly ghastly things like female circumcision.

Homosexuality is a human universal – it exists in all cultures. Current science also indicates that it is genetic and not a “lifestyle choice”. Of course, by definition, it results in zero reproductive success. Why then is it universal? Again, two theories attempt to explain it. The first says that homosexuality is a by-product of hyper-heterosexuality. By this I mean that a set of genes that normally result in robust heterosexual behaviors can sometimes carry the genes that can cause homosexuality. If there are five sons and four carry the hyper-hetero genes while only one is homosexual, then the overall reproductive success of the four sons with the hyper-hetero adaptation will outweigh the lack of reproductive success of the homosexual brother. The second theory applies the concept of inclusive fitness – the occasional homosexual sibling will still be part of the family and still help raise children and provide resources, making the family unit stronger.

Practitioners of the evolutionary perspective often fall prey to the teleological fallacy, the belief that evolution is proceeding along some preordained path to a predetermined conclusion. This is sometime referred to as “progressivism”. Evolution should not be anthropomorphized. It is a process, not a sentient being. Any adaptation that is beneficial will be passed along, no matter what direction it moves us in. As for “just so” stories, it can be tempting to start at the end of the evolutionary process and then attempt to reason backward. We evolved a fear of spiders to protect us from the danger of spider bites. Sounds good, right? But spiders have never posed a great threat to humankind, in modern or ancestral conditions. More likely, we have devloped an understandable aversion to the fast, unpredictable motions that spiders tend to make.


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