Laws of Human Behavior

How evolution has changed the scientific face of psychology.

Posted Jun 02, 2018

Syda Productions/Shutterstock
Source: Syda Productions/Shutterstock

The other day, I was talking to a guy with a physics background. He said that he is very fond of the field of psychology, but expressed concern about the fact that, unlike physics, it is “a soft science” that does not have any universal laws. Well, we didn’t have time to get into it — but, in fact, while I actually used to agree with this sentiment, I don’t anymore. My appreciation for the evolutionary perspective in psychology has totally changed this in my mind, as I have dug more deeply into the field over the past two decades.

The basic proposition of evolution is, actually, a universal law and logical truism. Renowned evolutionary biologist George Williams (1966) put it this way: Evolution is nothing more than a “statistical bias in the rate of perpetuation of alternatives.” Evolutionary psychologists take this reasoning and apply it to our understanding of behavior. As such, evolutionary psychologists always think about the processes that we study as following some basic natural laws.

Here, I demarcate two of the most basic ideas in the field, framed as scientific laws with derivative principles that follow.

2 Basic Laws of Psychology

From the evolutionary perspective, there are, in fact, many laws that underlie human behavior. Two of the most basic are related to “behavioral adaptations” and “evolutionary mismatch” (each of which is, ultimately, derived from the law of natural selection, which simply states that those qualities of organisms that are relatively likely to be selected naturally are more likely to exist in the future compared with alternative qualities). Importantly, again, these are only a subset of the many laws that evolutionary psychologists have documented as underlying human behavioral phenomena.

Law #1: Behavioral adaptations are Darwinian adaptations, and like any Darwinian adaptations, they ultimately serve the function of increasing the probability of survival and/or reproduction.

A behavioral adaptation is any psychological feature that was naturally selected and came to characterize a species because it helped increase the survival and/or reproduction of individuals in that species who displayed that adaptation under ancestral conditions (see Geher, 2014). While it takes a great deal of effort to scientifically document the existence of a behavioral adaptation, with the right data-collection processes, and a lot of blood, sweat, and tears, it can be done (see Schmitt & Pilcher, 2004).

Consider the fact that people across the globe find babies’ faces irresistibly cute (see Kringelbach et al., 2016). Well, this is a behavioral adaptation. Ancestral humans who found these faces cute were more likely to pay positive attention to their babies. And this would have led to increases in the probability of those babies successfully surviving and, ultimately, reproducing — passing along this trait (of responding positively to baby faces) into the future.

The broader point is that behavioral adaptations follow a lawful path that follows Darwinian logic. If a behavioral process or pattern can be documented to truly be a Darwinian adaptation, then we know several things about that process or adaptation with law-like confidence: We know that it is the result of an evolutionary process, such as natural selection. We know that it, on average, had the effect of increasing the probability of the survival and/or reproduction of our ancestors. And we know that it exists in some capacity across various human populations (because this is how adaptations run). We know its function, and we can use this knowledge about the adaptation to make all kinds of scientific predictions related to it.

So we can think of the basic idea of a behavioral adaptation as a law of psychology.

And this law, then, leads to various derivative principles that follow. In fact, we can think of the various behavioral adaptations that have been documented by scholars in this field as the derivative principles that follow from this basic law, such as:

  • The human emotion system serves to help people communicate with one another (Ekman & Friesen, 1986).
  • During the adolescent years, humans show an increase in behaviors that comprise intrasexual competition (Buss, 2003).
  • Whether people utilize a “fast” approach to life (reproducing early and often) or a “slow” approach to life (reproducing later and giving more attention to few offspring) is shaped by the degree to which one’s early environment is stable (Figueredo et al. 2008).

This is just a small sample of the principles that have been documented by scholars in this area. (For a more detailed summary, see my book, Evolutionary Psychology 101.) My broader point is that the idea of a behavioral adaptation has all the hallmarks of a scientific law — and several specific adaptations that have been uncovered can be now thought of as principles that can be used to guide future research questions.

And this is exactly how science works.

Law #2: Evolutionary mismatch, which exists when the modern environment of an organism is mismatched from the ancestral environment of that organism, will lead to demonstrable outcomes.

A basic premise of Darwin’s take on evolution is that organisms were shaped by natural selection to have features (both physical and behavioral) that fit with the details of a particular environment. Evolutionary mismatch (Giphart & Van Vugt, 2018) exists when the organism, in some objective kind of way, finds itself in an environment that is mismatched from the ancestral environments that surrounded the evolution of that organism. A simple example would be found if you tried to plant a palm tree in upstate New York. That plant would not survive the winter. That is because the adaptations of that plant are matched to more temperate conditions; its ancestors evolved under temperate environmental conditions.

The idea of evolutionary mismatch is a derivative of the basic law of natural selection. And it acts as a scientific law, based on logical assertions. Further, as is the case with the law of behavioral adaptations, we can think of the basic law of evolutionary mismatch as leading to various specific derivative principles that have been documented, including:

  • Modern human taste preferences were adapted for ancestral conditions in which drought was common, and they are mismatched from modern conditions, where many kinds of processed foods are common, and drought is rare (Keefe et al., 2006).
  • In modern human environments, people are more able to engage in deindividuated behavior than was true during the bulk of human evolution. And when people are deindividuated, they are more likely to engage in anti-social behaviors (Figueredo et al. 2008).
  • Under ancestral conditions, children engaged in free play in mixed-age groups and did not participate in formal educational systems. Modern educational systems are mismatched, in many ways, from such an ancestral environment (Gray, 2011).

Again, this list is the tip of the iceberg. Each of these particular kinds of mismatches has been documented by a variety of sources, and each can now be thought of as a principle in its own right, capable of leading to testable hypotheses to ask new questions and to uncover new information about the nature of who we are.

Bottom Line

Some people still think that psychology is a “soft science” devoid of any “laws” that guide the work in our field. While that may have been true in the past, the marriage of psychology and Darwin’s ideas on evolution has been a true game-changer for the field. The idea of a behavioral adaptation is a law in the scientific sense — based on the logic of natural selection. Similarly, evolutionary mismatch, which has powerfully generated various principles of behavior, can be thought of as a scientific law, similarly rooted in the foundation of natural selection. If you are a scientist, then you know better than to argue with the idea of natural selection. Thanks to the principles of evolution, there are laws that we have documented that underlie human behavior. Thus, the field of psychology does have basic laws. Next time someone tells you that ours is a soft science, don’t be afraid to pull the Darwin card.

    * You might be reading this section and thinking that it might be good to elaborate on this idea and write a broader, more thorough academic treatise of this subject, spelling out a broader array of evolutionary psychological laws and their derivatives. I would not disagree — and would very much welcome such a project being spearheaded by an inspired student or intellectual colleague. Such a project would make a great journal article and/or perhaps master’s thesis or dissertation. 


Buss, D. M. (2003). The evolution of desire: Strategies of human mating (Revised edition). New York: Basic Books.

Ekman, P., & Friesen, W. V. (1986). A new pan-cultural facial expression of emotion. Motivation and Emotion, 10, 159-168.

Figueredo , A. J. , Brumbach , B. H. , Jones , D. N. , Sefcek , J. A. , Vasquez , G. , & Jacobs , W. J. ( 2008 ). Ecological constraints on mating tactics. In G. Geher & G. Miller (Eds.), Mating intelligence: Sex, relationships, and the mind’s reproductive system (pp. 337–365). Mahwah, NJ: Lawrence Erlbaum.

Geher, G. (2014). Evolutionary Psychology 101. New York: Springer.

Giphart, R. & Van Vugt, M. (2018). Mismatch. Robinson.

Gray, P. (2011). Free to Learn. New York: Basic Books.

Kringelbach M. L., et al. (2016). On Cuteness: Unlocking the Parental Brain and Beyond. Trends in Cognitive Science, 7, 335-358.

O'Keefe JH Jr; Cordain L; Jones PG; Abuissa H. ( 2006). "Coronary artery disease prognosis and C-reactive protein levels improve in proportion to percent lowering of low-density lipoprotein". The American Journal of Cardiology 98 (1): 135–39. doi:10.1016/j.amjcard.2006.01.062. PMID 16784936.

Schmitt, D. P., & Pilcher, J. J. (2004). Evaluating evidence of psychological adaptation: How do we know one when we see one? Psychological Science, 15, 643-649.

 Williams, G. C. (1966). Adaptation and Natural Selection (link is external). Princeton University Press, Princeton, N.J.