Evolution: The secret to all of human behavior
Why do we crave unhealthy food, hate exercising, desire to be rich, and want to look young forever?
Because it feels good? But why do these things feel good? If you wish to understand human nature and the fundamental cause of all our idiosyncratic actions, you have to understand evolution.
Every living thing you see today, from bacteria to blue whales, and even yourself, is a product of an ongoing 3 billion year-long game among replicators.
Known as natural selection, this game is an eternal competition among these replicators. Those that are most efficient in surviving (resource gathering and predator avoidance) and making copies of themselves, win the game and move on to the next round. There is a constant trade-off between those two functions (survival and replication), which results in many different strategies being employed.
Humans are a subset of characters in the massive game of life, and the rules of the game apply no differently. Rather than being born as blank slates, our minds have been shaped by evolutionary pressures, creating domain-specific cognitive problem-solving modules and motivational drives that have helped us survive and replicate. That’s not to say that culture and socialization play a strong part in shaping our development and thinking, but the basic cognitive equipment we possess and the reasons why we developed them are largely explained by evolutionary forces. These core drives can be grouped into 4 fundamental motivations of human behavior: Survival (greed, fear), sexual selection, kin selection, and reciprocal altruism.
Survival and natural selection
Hardwired into every living organism is the impetus to survive, along with a host of motivations, fears, and behaviors that aid its survival. However, we currently face a major problem. Most of our genetically programmed drives are severely mismatched to our modern environment, triggering a multitude of problems ranging from obesity to anxiety.
Why we crave fatty and sugary food but hate exertion and exercise
We used to live on the razor-thin edge of energy balance, surviving on the margins of calories consumed versus calories expended. Every tiny morsel of food had to be painstaking extracted from the forest or chased down through brutal endurance hunts. We constantly craved food and calories because it literally meant survival. Conversely, saving energy by minimising movement was a survival instinct. We feel lazy because our bodies had to compute if using up our energy was going to be worthwhile.
**A matter of taste
**Why do we have 5 specific taste receptors, salty, sour, sweet, bitter, and umami? Taste itself does not exist in objective reality. A lemon is just a bunch of atoms; it does not have any intrinsic “sourness”. The sensation of flavor is a constructed property in your mind in response to specific molecules hitting your tastebuds. We evolved receptors to these flavors because they are adaptive to survival.
- Sweet: To detect calorie rich objects containing sugar (saccharides) in the environment.
- Sour: Picks up citric acid levels to warn us that a certain fruit or animal is unripe or potentially hazardous to consume.
- Bitter: To detect poisonous substances containing quinine.
- Salty: Our bodies need minerals, salt receptors drive us to consume necessary electrolytes for survival.
- Umami: To detect the presence of glutamate, which tells us that a substance is amino acid rich.
Our calorie seeking imperatives have not changed in such short evolutionary timescales, but our current environments have transformed dramatically. We still operate with a mindset of extreme scarcity, craving calorie dense foods in an environment of abundance. This means that maintaining neutral energy balance is now an enormous exercise in willpower - we fight a daily battle against every natural instinct. It’s not just that we have greater access to food, but the foods available to us are incredibly unnatural. When we take a bite of a cookie, we taste sugar at concentrations hundreds of times of what is naturally found in our prehistoric environments. This floods our brains with dopamine, reinforcing strong “do it again” pathways to secure the next hit. Despite the obvious health implications, sugar remains the drug of choice for most of us.
**Why we’re stressed all the time
Stress is an adaptive evolutionary mechanism. It’s meant to be a helpful response to face an immediate threat. In ancient times, we often faced life-threatening situations like being attacked by a neighboring tribe or a tiger. The acute stress response activates the sympathetic nervous system, causing our body to release adrenaline and cortisol that helps us to quickly mobilize energy in times of an emergency. The problem we face in a cushy modern society is that none of these threats exist. In the absence of these threats, we extrapolate and internalize abstract dangers: potential loss of work, stress from relationships, worries about the future. These “threats” are not acute and temporal, they permeate our day to day lives and constantly linger on our minds instead. Because our bodies still have the same hardware and have not evolved to cope with modern environments, our acute stress now becomes chronic, resulting in an epidemic of anxiety across most civilized populations.
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Why we’re never happy and constantly jealous of others
Jealousy was an important driver of success in the past. If your neighbor was gathering better food or growing more crops with the same amount of land, that person probably knew something you didn’t. Jealousy would drive you to find out more information because without that information, it’s likely that you would be outcompeted in resources and differentially selected out of the gene pool. It was a mechanism developed to tell you where you stood within your tribe based on how well everyone was doing. If you were in the bottom rungs, something had to be done because you were at risk of not surviving. The problem once again arrives when our ancient genetic algorithms crash headfirst into modern times. Instead of peering into your neighbor’s crop, you now have access to a handheld virtual portal that shows you how millions of other lives are thriving in unimaginable ways beyond your means. That adaptive mechanism to help contrast your competition turns upside down, and you’re faced with unresolvable jealousy that leads to perpetual unhappiness. Evolution did not equip us to be happy. A squirrel that found a single acorn and experienced perpetual bliss after was quickly wiped out of the gene pool. It equips us to survive - happiness is our own problem to solve.
**Why we’re afraid of ghosts
**Ok, there’s an implicit assumption here that ghosts don’t actually exist to begin with, but why are we still so afraid of them? Fear is one of the most powerful emotions. It’s powerful for a good reason: predator (or murder) avoidance. An ancestor that was cavalier about risks and unclear signals (ignoring rustling in the bushes), was in grave danger of making an error that nothing was actually there when there was a tiger lurking. This is called a type 2 error in statistics, otherwise known as a false negative. Our decision-making systems have been sculpted by evolution to avoid deadly type 2 errors (believing there is no tiger when it’s actually there) and be rather permissive of type 1 errors (believing that there’s a tiger when there actually isn’t). Type 1 errors are mostly harmless, taking up minimal energy to avoid versus a fatal incident. But it’s also what leads us to identify patterns in the noise when none exists. Someone falls ill when they enter a certain part of the forest, best to avoid that part of the forest in the future, lest we anger the spirits - the birth of superstitious behaviour. Because evolution forces us to be overly risk adverse, we end up fearing things that don’t exist, while simultaneously believing things based on loose patterns and anecdotes. The perfect recipe for ghost stories.
Sexual selection
Survival isn’t enough. The main point of the game is to pass down your genes, and this creates a whole new dimension of strategies. There are two major algorithms that operate in this space: how to make yourself as viable a candidate as possible so that you can pass your genes, and how to pick the best mate so that your progeny have the highest chance of replicating again. Your success as a living organism was determined by your ability to execute these two algorithms simultaneously.
Think about how fast it takes to evaluate if someone is hot or not. Whether you’re consciously aware of it, the main point of assessing hotness is to assess genetic viability. In a split instant, your brain runs finely tuned algorithms to process hundreds of different variables to make a calculation of hot or not. As with anything, culture plays a big role in shaping perceptions of beauty. However, there are well documented universals across cultures, which indicates strong evidence that many of these preferences are innate - a result of millions of years of the same selection processes playing out across uncountable generations.
Admittedly, the following paragraphs are going to appear rather crude and objectifying. It’s in no way an endorsement of what’s “right”, just an exploration of the causal factors evolution has built into our cognitive equipment. Broadly speaking, males look for signals of fertility (to ensure their genes are well passed down), while females look for signals economic viability (to ensure their offspring have sufficient resources).
When you assess how attractive someone is, the amount of information to evaluate is enormous from a computational perspective, yet a judgement is produced almost instantaneously. From a straight male’s perspective looking at a female here are some of the factors that are processed and the reasons why.
Youthfulness: Looking young signals a higher probability of reproductive viability. The older you are, the total amount of potential offspring over your lifetime decreases, and the risk of genetic complications increase. Our brains are quick to recognize this and incorporates it into a factor of “hotness”. There are arguments made to distinguish between hotness and beauty. People can age well and be considered beautiful, but hotness is something that objectively decreases because it’s interpreted as an indicator of reproductive potential.
Symmetry: Phenotypes (or physical instantiations of your genome) represent the underlying complex interactions of your genes. Having asymmetrical features is an indicator that your genes and its interactions to produce your outward phenotype likely contain more errors. Symmetry is a universal signal in the animal kingdom of high quality genes, giving an automatically association of beauty because the organism likely to be genetically fitter.
Blemishes: Having blemishes on your skin in the past was usually an indication of some sort of underlying disease or condition. Evolution has “priced” in this feature as unattractive because it carries a risk of lower genetic viability. This is why cosmetics is such a gigantic industry.
Waist to hip ratio: Turns out there’s an “ideal” waist to hip ratio that holds across all cultures. A meta-analysis found that this held true even across societies that had no western interaction (escaping the pollution of “western” beauty standards), and even more remarkably, across congenitally blind people (they were given plastic models to hold). This waist to hip ratio probably indicates a higher probability of offspring viability.
Pupil dilation: Both men and women subconsciously indicate a higher level of attractiveness when shown pictures of faces where their pupils had been artificially enlarged. Pupil dilation occurs when someone is engaged or interested. We are able to pick up this subconscious cue and we reciprocate by finding that person more attractive.
While most of the factors above describe male preferences, many of them apply to female preferences too. However, as mentioned earlier, females place a much higher weight to status and hierarchy (to secure resources for their offspring) as compared to males.
Wealth and status: Humans are hierarchical social creatures. Going up the ladder in the tribal hierarchy usually meant greater access to resources and higher chances of offspring survival. Females tend to look for these traits, whether explicitly (understanding a need for a secure financial future), or implicitly (simply subconsciously associating males with nicer cars as more attractive). Males are therefore driven to pursue outward expressions of status, usually by climbing up the social hierarchy or by gathering wealth.
Masculine features: The development of masculine features and behaviours is an indirect proxy for testosterone levels. At face value, more masculine features represent higher testosterone, which may indicate higher aggression levels and dominance in the hierarchy. For many females, one strategy would be picking out strong physical features that would typically ensure higher genetic quality and status within the tribe. However, this is a double-edged sword. Females need to ensure the success of their offspring, and picking highly testosterone-charged males might not always be the optimal strategy. They also need to ensure that males are willing to commit to them (usually in some form of a monogamous relationship) and will be willing to make sacrifices to share the burden of child-rearing. These traits are more strongly associated with males with more feminine features. Hence the competing interests make calculations on physical traits more complex, depending on factors such as short term reproductive viability and long-term shared parental investment.
**Costly signaling
**Natural selection and sexual selection can often be at odds with each other. The main example is the act of costly signaling, where one sex adapts traits to signal fitness to the other sex at the expense of optimizing its own fitness. The classic case would be peacock tails. It grows a beautiful but burdensome tail that puts it at a higher risk to predation. However, the tail is also an expensive but honest display of genetic fitness. It’s saying that it has the quality of genes to pull this off, whereas suboptimal males would not be able to. The most obvious form of this in humans is conspicuous consumption. We buy cars, branded goods and other luxury items that clearly do not have any benefit to our survival or our offspring. We prioritize self-presentation over economic efficiency - costly signaling in action.
**A side note to ultimate goals versus proximate goals
**The ultimate goal of evolution is successful reproduction. However, we do not have conscious access to these ultimate goals. Instead, evolution rewards us to chase proximate goals, such as wanting to get rich (to feel powerful), putting on makeup, wanting to have sex. In fact, because we are only aware of proximate goals, we often subvert the ultimate goals in pursuit of proximate ones in modern society. The obvious example is the use of condoms. Evolution has made sex pleasurable for good reason - it’s the most critical activity required for the propagation of genetic material. But we’ve now subverted the act by chasing the dopaminergic rewards that come from the proximate goal while actively preventing the ultimate goal. There’s also a reason why men would rather go out to bars and chase women, instead of lining up to go to the sperm bank where they could systematically achieve much higher success in passing down their genes.
Inter-sex conflict
There’s no question that male and females have different reproductive strategies. The cost of reproduction is much higher for females, requiring significant investment on their end. For males, the physical investment is often negligible. Hence, females tend to be more more selective with their mate choice and sexual promiscuity (these traits have also been co-opted culturally to promulgate virtues of abstinence). Males can however pursue both strategies, reproducing as frequently as possible, reproducing less but investing more resources to their children, or balance both simultaneously. This leads to inevitable conflicts in initial mating strategies. Women are usually in search of a long-term partner to ensure resource stability to their offspring, whereas men are just trying to get as many sexual encounters as possible. Both sexes often employ techniques to rig the game. Women may start out with under the pretense of a casual fling, slowly forming emotional attachments and luring men into longer-term relationships, whereas men can feign the desire for long-term commitment just to get to sex. Throw in some emotional dialogue, and you have the makings of every romantic drama.
Infidelity
Statistically speaking, the most dangerous person in a women’s life isn’t some random robber or murderer, it’s their male partner. The cost of infidelity to the male would mean the catastrophic end to his genetic line, hence the high chance of intense jealousy and impulse to react violently to any threat or perceived threat of infidelity. This is in no way condoning or justifying violence and domestic abuse in any form. It’s simply providing an evolutionary account of why so many of these horrific cases happen across the world. Males have the impulse to cheat because it secures them a costless way to pass their genes down. Females usually cheat because it can provide superior genetic variety and potentially secures resource from another male.
The different sexual strategies and feelings of jealousy are all ancient artifacts of evolutionary design. The world we live in today, where most sex occurs without the intention of producing children, makes most of these impulses irrelevant. Recognizing the roots of these traits and emotions is liberating. We don’t have to be beholden to them and other social constructs. We can decide which rules are beneficial and which are redundant legacies of our evolutionary history.
It was said by a famous sociobiologist that every human interaction makes sense in light of sexual selection. It explains much of our desires and behaviors. Though at this point, I want to emphasize that it’s impossible to reduce everything to evolutionary factors. Not only that, just because something has been programmed by evolution, it doesn’t mean we can’t change our perspectives through culture or deliberation of values. Human beings are complex emotional creatures, but evolution provides a reference point to understanding of our behaviour.
Kin selection
Now that we’ve covered survival and sexual selection, the next question is: “Why do we care about our relatives?”. There’s a reason why we’re much more likely to risk our own life to save a direct sibling over a cousin and much less likely to risk anything over a complete stranger. From a genome perspective, direct relatives share a substantial number of genes. Direct siblings share on average 50% identical genes, nephews 25%, and cousins 12.5%. Mathematically speaking, if an individual were to lose its life to save two siblings, four nephews, or eight cousins, it’s “fair trade” in evolutionary terms. While there is no direct benefit to us by risking our lives, evolution only cares about genes, and our behaviors are ultimately dictated by how effectively these genes were able to replicate.
**Parent-offspring conflict
**You might assume that since the ultimate goal of evolution is successful replication, every parent’s objective should be the total devotion of energy and resource to their child. But there are inherent conflicts in the parent/offspring evolutionary strategies. A child has a stronger incentive to maximize the extraction of resources and demand as much investment from its parent. Whereas for parents, they need to balance the investment between a single child and the potential of all future offspring. In baboons, moms evolved to wean their kids of milk as soon as they can feed themselves, whereas baboon kids evolved to delay the weaning for as long as possible. As long as the mom nurses, she is unable to ovulate - leading to parent-offspring weaning conflict with a lot of irritable moms and tantrum-throwing baboon kids. I’ll leave you to extrapolate the human analogies yourself.
No matter how you look at it, biology often reveals uncomfortable truths about the nature of human behavior. Just because something has an evolutionary cause does not mean it’s defensible in any way. But we need to stare down at the facts, not look away, and decide how we want to live in spite of our evolutionary origins.
Reciprocal Altruism
The final piece of the four fundamental drives. This is what enables social species like humans to help each other even though there might not be an obvious immediate advantage to our genes. Ultimately, the reasons are still selfish. Why would an organism take a cost to its fitness to increase the fitness of another individual? (Fitness used here is the evolutionary term for odds of survival). The answer is simple: we expect reciprocity.
The origins of altruistic behavior and the different strategies employed are shaped by game theory. The details are too complicated to dive into here, but essentially cooperation was developed as a means of survival. Those that were willing to empathize and help others were more likely to receive help in the future. Those that cheated by not cooperating might have gotten some mileage, but they would eventually get caught and not receive additional benefits from the tribe. We still still do the dance of exploitation (getting favours) and altruism (giving favours) in our daily lives, finding our own optimal balance, and punishing selfish people regularly.
Social anxiety
I’ve heard this phrase before that some people are more afraid of public speaking than dying. It may sound ridiculous, but there’s a strong evolutionary basis for this fear. When we lived in small tribal groups, having your reputation ruined or being shamed by the group was equivalent to a genetic death sentence. The likelihood that you will successfully find a mate to reproduce if you became an outcast was extremely low. This is why we’re highly tuned to think about how people think about us. We’re essentially playing a multiplayer game where you had to remain in good favour with your other tribe members. Even though we live in a modern world where the opinions of others are mostly inconsequential, that emotional module that creates fear and anxiety from social interactions has not disappeared.
Exclusion from a tribe is one of the most punishing experiences for this same reason. As social primates, the fear of not being accepted is one of our greatest concerns. This is evident in daily life. People often prioritize the need to feel accepted over the need to be correct. We often derive our opinions and values through our group affiliation - whether it’s political, social, or familial. The effect of social conformity is so strong that people are willing to override their most fundamental imperative - to survive - for the sake of group ideals such as war, suicide bombings, and dismissals of vaccine science.
**Us versus them
**Coalitional instincts allow us to cooperate with non-relatives and work together on projects that would only be possible through mutual collaboration. This instinct to band together as a tribe allowed humans the accomplish remarkable feats unattainable by non-social animals. However, there’s a dark side to our innate tribalism. Because we are much more likely to form alliances with in-group members and we needed to be wary of neighboring tribes, we were left with the ability to rapidly discriminate based on seemingly arbitrary attributes. At times of conflict, it would have been unadaptive if we viewed a warring tribe as similar to us. It would have left us without the ability to galvanize our assault, probably resulting in the deletion of our non-discriminatory genes from the pool. Studies have shown that grouping children by arbitrary characteristics, such as giving them red or blue t-shirts, were enough to trigger hostility to the out-group and increased empathy within the in-group. Freud called this the narcissism of the small difference - we look for tiny variations in physical appearance or culture, generalizing them to create identities and eventually discriminating between them.
There’s another more insidious reason why we’re afraid of outsiders. When we interact with the out-group, there’s a balance between introducing new genetic material to the pool (explaining some attractiveness to foreigners), to the introduction of pathogens that could wreck a tribe without a developed immune system. These are unconscious programs we have running in our brains, and they are occasionally exploited through political means. This is why branding certain groups of people as “unclean”, “dirty”, or disease-ridden is so toxic and potent. It taps into our natural aversion to out-group contamination, making it highly effective because the ideas attack us on a subconscious level. In our modern world, it’s a malicious and weaponized concept that continues to be used to subjugate different classes and promulgate racist and xenophobic notions.
**It’s just the beginning
**I’ve covered some of the fundamental forces of evolution that drive human behavior, but the reality is that I’ve barely scratched the surface. Humans are infinitely complex. Culture (norms, memes, values, traditions) plays a major part in shaping what we do. However, evolution remains the binding principle that guides most of the understanding in biology. Once you are able to view human behavior through the prism of evolution, you begin to see everything in a new light.