2. Evolutionary Psychology

Evolutionary psychology is the scientific study that looks at how one can understand behaviors, thoughts, and feelings as the product of evolution through natural selection. It is a combination of psychology and evolutionary biology. Organisms have developed a variety of physical and psychological adaptations conducive to survival and reproduction. Evolutionary psychology is the exploration of these psychological mechanisms. I’m going to describe the nature of the mechanisms and then look at how that plays out through an example. 

You probably have a basic idea of how a computer works. It receives input, then processes this input according to a series of preprogrammed instructions, subsequently producing an output. It has memory for storage and consists of the physical hardware and the processing software.

The brain is also an information-processing device, and there are similarities in operation. The evolved psychological mechanisms are like the preprogrammed software. They are receptive to input from the environment, which arrives through the five senses. The appropriate mechanism activates as it recognizes which adaptive problem it is facing. It then responds according to a set of decision rules. The output is an emotional response or a behavior directed toward a solution. The mechanisms interact with each other; sometimes they are in conflict, at which point they prioritize depending on circumstance. You are not conscious of most of what is taking place. 

Computer software is made of code, or symbols, which programmers write. The brain’s software, or psychological mechanisms, are made of neural circuits, which tens of thousands of genes build as part of the nervous system. Behaviors, thoughts, and feelings are a product of the nervous system. These neural circuits are networks of interconnected neurons, or brain cells, which communicate through electrochemical signals. The circuits are domain-specific. This means that each one solves an individual adaptive problem and is concerned only with a selective range of information. The mechanisms need to be as specific and complex as possible to secure a good outcome, and there needs to be enough of them to cover the important scenarios. This is most efficient because humans generally have faced the same adaptive problems throughout history. These are situations related to survival, mating, parenting, assisting relatives, and social interactions. However, because novel circumstances arise, there are also a few domain-general mechanisms. These relate to general intelligence, reasoning, memory, and classical conditioning. 

Here is where the brain and a computer differ: The mechanisms are designed to work on average; there is vast complexity and uncertainty in the environment, and often many possible responses. We’ll look later at how exactly decisions are made; the brain essentially runs the input through the relevant programs and comes up with an output that is the result of an extremely complicated cost-benefit analysis. This analysis is only as accurate as the information the brain has access to by way of innate structures, memory, and current input. Remember that evolution takes time. The mechanisms have evolved efficiently, but if the environment changes too quickly, they can produce maladaptive responses.

The blueprints needed to build the psychological mechanisms are in the DNA of the genes. We are not born as blank slates; we already have the software written, which develops as the organism grows. An organism needs to know how to act as soon as possible within its lifetime. Learning is often too costly. An animal doesn’t have the luxury of experiencing that a predator in pursuit may be fatal—at that point it’s too late. Learning from the environment can happen only because the structures are already in place. Which language you speak depends on your surroundings, but you won’t speak any at all unless you have that specific set of neural circuits. The environment can certainly affect the cost-benefit analysis and therefore the behavior, but it doesn’t change the actual mechanism. Each species has a slightly different set of mechanisms because they face different adaptive problems. This is also true of male and female sexes. 

Now let’s look at a mechanism in more detail. One example is the disgust response. The domain-specific problem it addresses is disease avoidance—a survival problem. First, you need an input from the senses to activate the mechanism. Common causes of disgust are contaminated food, illness, poor hygiene, open flesh, or bodily fluids. This is because they all pose an immune threat. (Incidentally, an individual’s wound may repulse you, but a scar may often impress you—this is because they survived possible infection and therefore have a high-quality immune system.)

Next, once an input activates the mechanism, it processes the information according to the rules. If you come into proximity with a scenario that causes disgust, then you move away, you don’t touch, and you close your nose and mouth to avoid contact. However, it’s not always so simple. Other mechanisms may need activation, and there might be some prioritization, so the decision rules come into play. For example, if you are starving with little opportunity for sustenance, and the food is only slightly contaminated, the cost-benefit analysis may direct you to brush off the mold and eat it anyway. Or perhaps you come across someone with a contagious illness, and this person is a close relative. You may wish to approach and offer assistance despite the risks (activating the kin selection mechanism). If this person is a friend, you might help them with the expectation of future reciprocity (activating one of the many mechanisms relevant to social relationships). Pregnant women have a heightened sense of disgust, often specific to foods, and this is part of a parenting mechanism. The fetus is especially susceptible to toxins. A mother doesn’t learn this; it happens automatically, and the mechanism directs her actions. 

These mechanisms, which complex genetic coding designs, can be specific. You don’t find your siblings disgusting in general (well, maybe in jest!). However, the thought of sexual intercourse with them is hugely aversive. The mating mechanisms are geared toward improving gene quality in offspring, and incest would be deleterious to the genes. It’s best that this is firmly and discriminatingly established within your nervous system. You simply won’t be attracted to a genetic relative, even if you were separated at birth and meet unknowingly later in life. There’s even a bit of failsafe—you are unlikely to be attracted to an adopted sibling because, despite the lack of genetic barriers, your nervous system will say no, “just in case.” 

The mechanisms often seem intuitive, and they are. What many people don’t realize is just how deeply they are ingrained. For example, the sound of running water is generally relaxing. This is because it is likely to be fresh and bacteria-free as compared to stagnant water. You can relax, and drink or bathe without fear. Traffic lights are red and green because we are good at distinguishing these colors. This is in part because it was helpful to be able to distinguish ripe from unripe fruit. We like alcohol because it is essentially extremely ripe fruit. 

Remember that the mechanisms have evolved to work on average. In some instances the circuits can be tricked or activated under the wrong circumstances. For example, body temperature will rise (as an immune response) simply by viewing images of disgust-inducing objects, even though pictures pose no threat. You can see how something as simple as the disgust circuit is not only complex but also crucially important to survival and reproductive success, and this is the same for all other evolved psychological mechanisms. 

To better understand how they affect us today, it’s helpful to study our ancestors, which is what we will do in the next section. 

*The information from this section is primarily from Evolutionary Psychology: The New Science of the Mind by David Buss.