How Evolution Actually Works

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Image credit: Birdwatchdaily.com

Today I read here on Medium an article that first appeared in the New York Times about “how beauty is forcing scientists to re-think evolution.” As I know a great deal about evolutionary theory and its real-world effects I was naturally curious.

The article was shockingly ignorant and served only to spread misinformation and simple-minded misconceptions. This was the basic argument, which I’ve paraphrased for sake of brevity:

The male bower bird has spectacular plumage. But this isn’t enough to attract a mate, so the male also constructs an elaborate bower using colorful materials scavenged from the local environment. But this too isn’t sufficient to ensure mating so when a female appears to inspect the bower, the male bower bird must execute an elaborate dance. Only then may the female deign to mate with him. So this “proves” that natural selection alone can’t be responsible for the creation of beautiful things because obviously it’s only the dance that counts, so why does the male have such resplendent plumage and go to the trouble of constructing the lovely bower?

The implicit assumption seems to be that animals can only use a single indicator of genetic fitness when assessing a potential mate.

I’d like to think even a first-grader could reason more adequately than this, but apparently my optimism is unfounded. No doubt the author of this appallingly simple-minded piece actually graduated from High School and perhaps even has a Bachelor’s degree in Tying My Own Shoelaces (With Only A Little Help From Mom).

Condign sarcasm aside, let’s look at why the argument is fallacious. To do so, instead of beginning with the hapless bower bird, we’ll look at a simplified example of human mate selection because, let’s face it, we like talking about ourselves more than we like talking about birds.

As with all mammals, human females bear the brunt of gestating and rearing offspring so females are the choosy gender. As their investment is greater and they can have fewer potential offspring in a lifetime, being picky is essential to maximize the probability of their offspring thriving and in turn passing on their DNA into the future.

So much, so obvious. Now in our thought experiment let’s go back a few hundred generations. Females want males that are tall, because being tall means having good genes and having secured good nutrition throughout development and all this means a higher probability of survival. So taller males get more mating opportunities and thus genes for tallness spread through the gene pool because short-gene males don’t get as many mating opportunities and so have fewer offspring and thus over many generations genes that confer greater height eventually predominate.

(Remember, this is a simplified thought experiment; in reality many different genes contribute to height.)

When we fast-forward a few thousand years, the result of this selection pressure is that most males are now reasonably tall. So human females consequently need an additional marker of genetic fitness in order to discern between potential mates who are now all more or less the same height. Let’s say the females start to look at facial characteristics because facial symmetry is an excellent indicator of genetic fitness and good nutrition. So now females require males to be tall and to be good looking (across all cultures, symmetry is equivalent to good looks).

Fast-forward again a few thousand more years. Now almost all males are tall and good looking. So females require yet another marker of genetic fitness. Let’s say that females start looking for mental characteristics such as intelligence. Once again, after some period of time, selection pressure will mean that height and symmetry and intelligence will all predominate across the population and all will be required by females considering their mating options.

Now it’s easy for us to understand why the male bower bird must do so much to attract a female. Time doesn’t stand still. Evolution is a constantly moving process, building on what has gone before. When females begin to require a new marker for genetic fitness they don’t abandon the previous markers because those are important and don’t stop being important. The male’s plumage remains an important indicator of genetic fitness, as does his ability to create an alluring bower.

Of course the picture isn’t as simple as the thought experiment above. In reality, especially with complex mammals, females select from among a great many markers of genetic fitness. Few males are tall and handsome and highly intelligent and strong and funny and skilled dancers and excellent musicians and outstanding jugglers, for example. True, we are all of us much better at these things than our ancestors of 400,000 years ago, but because there are so many indicators, different females will prioritize different characteristics.

This is especially true today when for the first time in the history of our species we can consciously practice assortive mating. Women who prize high intelligence will tend to mate with highly intelligent men; women who prioritize height and strength will tend to mate with tall muscular men; and so forth. But the core point remains the same: very few human females will reduce mate selection to a single trait. Selection is always relative to today’s pool of candidates, not relative to the candidates of tens of thousands of years ago, and so multiple desirable traits will all be taken into consideration.

So one type of beauty is simply our reaction to important markers of genetic fitness. There is, however, a second type of beauty that is also entirely explained by evolution.

We respond to certain environments favorably. Who doesn’t feel comforted by seeing a sylvan glade through which a babbling brook runs sparkling? This is because we’re hardwired to respond positively to indicators of environmental suitability. It’s a lot easier for us to survive in a pleasant lush bucolic environment than in a barren hot desert. Our reaction to environmental cues of plenty is to feel they are more satisfying, more attractive, than bleak alternatives. We call this response “appreciating their beauty.” That’s why we prefer paintings that trigger this type of response over paintings that make us want to vomit. The root cause is because ancient humans who preferred resource-rich environments thrived whereas those who selected resource-poor environments tended not to. Thus over time we all inherited the genes that prompt us to prefer resource-rich environments. We find them beautiful.

As for our response to music, our brains are hardwired pattern-recognition engines. When we hear a piece of music we deem beautiful, it’s because we’re responding to the interplay of harmony and melody and rhythm. In one way the music is a fitness indicator (for the composer and for the musicians performing the piece) and in another way it feeds our need for patterns, which is the basis for nearly all higher brain function.

Our perceptions of beauty in either other animals or in the environment at large all have a basis in fundamental evolutionary processes.

Hopefully this brief explanation shows why the NYT article was so appallingly ignorant and misleading. Given that the USA isn’t exactly over-burdened with people who have an adequate grasp of evolution, the very last thing we need is for a well-known rag to pump out arrant nonsense.

Anyone who wants a layman’s guide to how evolution actually works can do no better than to read the works of Richard Dawkins, who for nearly two decades tried to explain evolution to the general public. The Blind Watchmaker is the place to begin, and Climbing Mount Improbable is a reasonable place to end.

Thanks for reading.

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Anyone who enjoys my articles here on Medium may be interested in my books Why Democracy Failed and The Praying Ape, both available from Amazon.

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