The rules of evolution are simple: (1) if a trait makes survival or breeding more likely, then that trait will tend to survive in the long term by being passed down the generations. (2) Gene mutation and gene mixing create new traits, which naturally vary in how much they promote survival.
Yet, the consequences of these simple rules are profound. Various facets of the world are hard to understand without taking evolution into account. Since our brains and bodies (as well as the natural world) were literally crafted by evolutionary forces, without that evolutionary perspective, you’re missing an important angle.
Here’s a list of human traits that seem hard to explain without considering an evolutionary element (along with possible evolutionary explanations for each):
Note: I’m not an expert in evolutionary theory, and none of these theories are provable beyond a shadow of a doubt. It’s important to remember that not all traits we have are evolutionary adaptive (for instance, they could just be vestigial, or side effects of other adaptive traits, or deleterious but not given time to be squashed by evolution, or random genetic drift, or better explained as cultural phenomena). Think of these as hypotheses for why these aspects of ourselves and the world are the way they are.
Possible Genetic Explanations for Things We Observe
- Why we have a sour taste capacity: probably to detect food spoilage (e.g., the bad chicken may smell and taste sour), as well as under ripeness (think of an unripened apple) and excessive levels of acid (think of old wine that has turned to vinegar). Small amounts of sour taste fine (or even good) to us, but more pungent tastes are usually bad.
- Why we have a salty taste capacity: probably because we die if we don’t replenish our salt since we need it for ion/water homeostasis.
- Why we have an umami taste capacity: probably to encourage us to eat peptides and proteins, which are used in many parts of our bodies (e.g., the composition of muscle). This is the most recently discovered taste capacity that seems to have gained substantial acceptance.
- Why we have a sweet taste capacity: probably to encourage us to eat sugars since they have calories that we use for energy to stay alive. It might also exist to encourage us to eat starches (which can taste sweet as they break down in our mouth), but some now argue that there might be a unique starch taste capacity.
- Why we have a bitter taste capacity: probably to detect poisons (e.g., many non-edible chemicals taste bitter, such as pesticides).
- Why we start to like bitter foods more once we’ve eaten them for a while: possibly because our brains initially assume they might be poison, but after eating them for a while, learn they are fine after we don’t get sick (hence why people can come to enjoy black coffee even though most younger people find it disgusting when they first try it).
- Why some plants have psychedelic effects: probably because they are “trying” to prevent animals from eating them (if it’s a plant that does not spread its seeds by being eaten) or because it’s “trying” to get eaten (if it spreads its seeds by being eaten). Different psychedelic effects from different plants on different animals may be more or less pleasant and may or may not be dangerous for survival.
- Why plants contain caffeine: possibly because it seems to be a natural pesticide for some insects, and possibly because it is believed to attract some types of bees.
- Why we have an “itch” sensory system: probably to detect insects crawling on and landing on us (which is really important when you live outdoors, though not so much when you live indoors).
- Why, when something lightly tickles your skin and produces an itchy feeling, the itch tends to grow worse until it is scratched: possibly because while you may be able to detect an insect landing on you, you probably can’t tell if it’s sitting still on you, so the itching sense is reminding you to scratch (i.e., the bug still might be sitting there even if you can’t feel it).
- Why some people throw up in cars: possibly because some poisons cause a mismatch between what you see and what you feel (and in those cases, it makes a lot of sense to throw up to get rid of the poison). In other words, a mismatch between visual stimuli and proprioceptive stimuli would be an indicator that you may have been poisoned and should throw up to expel it. Being in a car happens to produce a similar mismatch of sensory input.
- Why we get sick of foods if we eat too much of them: probably a form of helpful encouragement to eat a varied diet (to get more balanced nutrition) so that we aren’t as likely to become malnourished.
- Why we sometimes have sudden cravings for non-addictive foods: possibly because the body senses we lack a certain important nutrient.
- Why symmetry is typically considered attractive: probably because various problems related to development in the womb and genetics that can affect survival or reproduction can produce asymmetry (in other words, symmetry is a little bit of evidence that a variety of things that could have gone wrong during gestation, didn’t).
- Why people find clear skin beautiful: possibly because some harmful infectious diseases can cause skin issues (though, of course, most skin issues are harmless)
- Why humans usually find babies cute: probably because it causes us to take better care of our babies and children (and our relatives’ children), which causes our genes to spread more effectively down the generations (and on the flip side, it causes us to be better-taken care of by adults when they have genes for liking cuteness – it is beneficial for the genes of both the adult and baby). Of course, that’s not the only force causing adults to treat babies well, and people seem to differ substantially in how value they put on cuteness.
- Why humans find baby animals cute: probably in part because we’ve purposely bred them to look cute to us (especially dogs) but also in part because babies of other species have features that resemble babies from our own specifies (e.g., helplessness, big eyes relative to the head, big head relative to the body, larger forehead, flatter face, etc.). I assume that the people I know who find (non-bred-to-be-cute) baby animals cuter than baby humans are outliers.
- Why there are so many diseases that are only likely to kill us when we’re old: probably because once we’re past the age of reproductive fitness, there is much less evolutionary pressure pushing to keep us alive (though there still is some, because we still might be useful for helping copies of our genes survive in others, such as in our grandchildren who we can help)
- Why obesity is common now in our society but doesn’t seem to have been a long time ago: probably because our drive to eat food (and calorie absorption systems) were designed by evolution for an environment where exercise was a built-in part of daily life, food was much scarcer, and the taste of food was not nearly as optimized for addictiveness as it is today. Hence many factors push us to eat much more than would have been typical. It’s possible that food was “healthier” way back when on average too, but that’s really tough to say, in part because diets now and back then both varied tremendously depending on location, and in part because optimal human nutrition is still not very well understood.
- Why sudden loud noises cause most people anxiety: probably because such sounds were a pretty good indicator of danger 20,000 years ago (e.g., a tree falling, lighting, a loud animal, an angry person)
- Why males are larger than females on average across nearly all large human groups: possibly because males used to battle with each other a lot more than females did (and so there was a sort of arms race in male size), and also possibly because males hunted more often than females (the larger average size of males may be an adaptation, e.g., for spear throwing, where body weight is helpful). Studies apparently show that the size difference between males and females within a species is correlated with the amount that males battle each other over mates, social status, or resources, though I can’t vouch for the reliability of these studies.
- Why your fingers get wrinkly when soaked in water for a long time: possibly to help us grip wet objects better (since according to at least one study, it seems to improve the gripping ability of wet objects) though this certainly could be a coincidence and some researchers argue against it.
- Why faces play such a prominent role in attraction even though most common facial differences have little or no direct useful function: probably because faces encode some other non-face related information (e.g., related to hormone levels and age) and also because they directly code a little bit of information about how attractive (on average) other people may find your son or daughter if you mate with that person (e.g., if birds find large beaks attractive their offspring will survive more if they have large beaks, all else being equal, even if beaks do not help in any other way).
- Why people who are blind from birth make facial expressions for some emotions (especially anger, contempt, disgust, fear, happiness, and sadness) that non-blind people can recognize at least fairly accurately: probably because these six social emotions are generally useful for survival when living in a group across a wide range of environments (by communicating important information to others) and so have been hardcoded by evolution in a form that others can recognize. It’s also possible that the studies that claim this finding were poorly designed, though.
- Why most people seem to have a gut reaction that incest is morally wrong: possibly an inbuilt mechanism to protect people from breeding with close relatives, which would have a much-elevated chance of producing genetic disorders.
- Why people get goosebumps: probably a (mostly) vestigial reaction for adjusting our hair follicles, which was programmed a very long time ago when our bodies had a lot more of it. Hair standing on end makes animals warmer when they are cold and increases their apparent size when afraid, to intimidate other animals (hence why cold and fear can create goosebumps). It may still be a bit useful for warmth because we have some hair on our bodies.
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