Evolutionary Logic

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The other day I was talking with someone about the basics of evolutionary psychology. She was very smart and motivated to understand this field. During our conversation, I was surprised to learn that each time I brought up the concept of evolutionary logic, she needed to be gently re-educated on this concept. This conversation made me think that there are probably a lot of people out there who don’t have a strong sense of this foundational concept in the field. This blog post is designed to fix this problem!

What is Evolutionary Logic?

I may be no Mr. Spock, but I have to say that I just love logic! My two favorite classes to teach are (a) Statistics and (b) anything related to evolution. Statistics is a fully logical approach to making inferences about how the world likely truly is. And I just eat that stuff up like candy!

Evolution is, also, based on logical principles first and foremost. In his classic text, Adaptation and Natural selection, renowned biologist George Williams (1966, p. 22) provides us with what is perhaps the simplest and most generalizeable definition of evolution. He writes: “… evolution is nothing more than “… a statistical bias in the rate of perpetuation of alternatives.”

So evolution, then, is actually based on a statistical set of ideas – and it ultimately follows its own logic. In short, what Williams means is that when there are various forms of some entity, forms that are, for whatever reason, good at replicating themselves relative to other forms are more likely than are those other forms to perpetuate into the future. This is just a logical assertion.

And since the foundational concept of evolution is just a logical assertion, we can totally dismiss any questions as to whether evolution is “true” or not – as we can simply say that it is a logical assertion that must be true by definition.

Anyway, getting back to the concept of evolutionary logic, we usually use this term as it relates to adptationism – or to our understanding of a psychological adaptation. The short version of this logic is as follows: If some behavioral patterns has been documented to be “adaptive,” then that means that individuals with the “adaptive” variant of that behavioral pattern, under ancestral conditions, were more likely to survive and reproduce than were individuals without that ancestral variant. And that is why the “adaptive variant” exists today. Logic. Evolutionary logic!

Following are three examples of evolutionary logic in action. The hope here is that once you understand how these three examples work, you’ll just totally get the concept.

Example #1 of Evolutionary Logic: Waist-to-Hip Ratio

A great deal of research conducted by evolutionary psychologists has shown that women with a waist-to-hip ratio of close to .7 are rated as relatively attractive (see Platek & Singh, 2010). This hourglass-like body has been documented also as being optimal for women being able to conceive offspring. Thus, this preference on the part of males looking for mates goes hand-in-hand with an actual adaptive outcome associated with increased reproductive success. And this is how adaptationism in evolutionary psychology rolls!

Under ancestral conditions, males who did not have the preference for women with the .7ish waist-to-hip ratio were less likely to successfully reproduce than were males with the preference for the .7ish ratio. Generations later, we are filled with males who show this .7ish ratio – and that is explicable via evolutionary logic.

Example #2 of Evolutionary Logic: Youthful Hair and Clear Skin

When you go to the drug store and go up and down the cosmetics aisle, you don’t see many products designed to make women look elderly. The hair dyes come in blonde, brown, red, and so forth. But you don’t see a lot of white or grey. Similarly, skin products that are “anti-wrinkle” are common. Skin products that are “pro-wrinkle” are not.

We can understand this all using evolutionary logic. Human females are only fertile during a window of life – between about the ages of 14-48 or so. Females outside this age range are unlikely to be able to bear offspring. Thus, males who, under ancestral conditions, had a preference for women who were beyond the boundary of menopause were less likely to successfully reproduce than were other men – even if they successfully were able to mate. Males who were forming intimate relationships with elderly women were not likely to pass on any genes that coded for a preference for elderly women – because these mateships were less likely to lead to offspring.

For these reasons, ancestral males who preferred women who showed markers of fertility – such as luscious blonde hair and smooth skin – were more likely than were other males to reproduce. Again, this is evolutionary logic at work.

Example #3 of Evolutionary Logic: Helping those Who Help

Evolutionary psychology goes well beyond the scope of human mating. As I argue in much of my work (see Geher, 2014), evolutionary psychology applies to all kinds of concepts in the broader field of psychology. For instance, much work in the field explores Robert Trivers’ (1971) concept of “reciprocal altruism.” This concept is straightforward – it is pretty much the idea that we are more likely to help others who have helped us in the past than we are to help non-helpers. The tendency to discriminatively help others who are, themselves, helpers is adaptive. Ancestors of ours who did not discriminate when it came to whom they helped out were less likely to be securing long-term help for themselves and were, thus, less likely to survive and reproduce compared with their discriminating counterparts who carefully and selectively made sure to help those in their communities who were likely to help them back.

Evolutionary logic again!

Bottom Line

Evolutionary psychology is cool for a lot of reasons. One of the main reasons has to do with the evolutionary logic that underlies so  much of the field. To think like an evolutionary psychologist is to be a behavioral logician – piecing together how some behavioral patterns, via processes such as natural selection, simply must be relatively prevalent compared with others.

While adaptationism is hardly the only concept in the field of evolutionary psychology, it is pretty foundational and helps us get very far in understanding how evolutionary forces have shaped modern human behaviors. Understanding evolutionary logic, which underlies the concept of adaptationism, then, can help us go very far in understanding why people act the way we do.

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