Tuesday, July 28, 2015

A Real Evolutionary Psychology

Image Source: Flickr
Some estimates suggest that, compared to women, almost twice as many men cheat on their spouses.  Why?

The answer seems obvious.  The more sex a man has, the more likely he is to get a woman pregnant.  The more sex he has with more than one woman, the more likely he is to get more than one woman pregnant.  The more women he gets pregnant, the more children he will have, and the more of his genes that will live on in future generations.  Selfish genes in action, as it were.

The poor woman is not so lucky, as getting pregnant once removes her from the system for at least 9 months, if not longer, practically speaking.  But why, then, do at least some women cheat, too?  With a little imagination, we can make sense of this.  It turns out that cheating provides an opportunity for the woman to get better genes from fitter donors.  She can maximize her limited opportunities to get pregnant and give birth.  It is a matter of quality, then, not quantity.

Or is it?

Speculations of this kind about the evolutionary origins of human nature are popular in some circles and such thinking is formalized in the field of evolutionary psychology.  Evolutionary psychologists contend that much of our behavior has been hard-wired into our brains via natural selection.  The field has given off much heat but very little light, but it remains popular.  This is unfortunate, as the heat generated by EP stands to keep people away from the light produced by more rigorous analyses of human behavior rooted in science, not pseudoscience.

Evolutionary psychology is not a science, it is “just-so” psychology in which people are observed to behave in certain ways, some plausible story about the problems faced by our ancestors is formulated to explain why the observed behavior would have evolved, and then observations that people do indeed behave that way are offered in support of the explanatory story.  This is circular reasoning at its finest.  (This is to say nothing of the gross misuse of heritability estimates in research on psychological traits, but that is for another blog post.)

Invoking Darwin, selfish genes, and DNA cannot save it from the clutches of pseudoscience.  So what is the alternative?

It turns out that learning is a much more powerful and plausible explanation for much of what is attributed to genetics by evolutionary psychologists.  Our brains are not hardwired with many special purpose modules guiding our behavior.  What has evolved is an exquisite behavioral sensitivity to our environment, allowing our behavior to be shaped by the pressures we face rather than the pressures our ancestors faced.  More than 100 years of experimental evidence supplies us a rich framework with which to understand human behavior (and the behavior of other animals).  There are, indeed, parallels between biological evolution and behavioral evolution, just not the kind proposed by evolutionary psychologists.

There are three processes critical to biological evolution: variation, selection, and retention (via replication).  As it turns out, these three processes are common features of both biological and behavioral evolution. At the behavioral level, behavior varies from one situation to another and from one time to another in the same situation.  Certain types of behavior will produce beneficial outcomes and some will not.  The beneficial outcomes "select" the behavior that produced them, leading to that behavior being repeated (due to changes in the nervous system) in similar circumstances in the future.

B. F. Skinner
Image Source: Flickr
We know about this process of behavioral evolution, and the details of how it occurs, chiefly from the work of the late American psychologist B. F. Skinner and his many students and colleagues.  Skinner famously discovered operant conditioning, a term he used to collectively refer to the basic laws governing most of human and nonhuman behavior.  Operant conditioning encompasses a relatively small number of very powerful principles, including reinforcement, punishment, extinction, and stimulus control.  Like evolution by natural selection, operant conditioning is a simple mechanism that gives rise to great complexity.

In Skinner's terms, behavior that produces favorable outcomes (reinforcers) is more likely to occur in the future (an outcome called reinforcement). Additionally, the behavior is most likely to occur in the future in situations that are similar to situations in which the behavior has been reinforced in the past. This acquired effect of the environment is referred to as stimulus control, and the controlling stimuli are called discriminative stimuli.  In this way, the reinforcer selects a relationship between a set of environmental circumstances (discriminative stimuli) and certain types of behavior.  That is, the reinforcer "reinforces" the relationship between the circumstances and behavior, meaning that the behavior is more likely to occur when those circumstances present themselves.  The opposite effect is seen with punishment, whereby certain behaviors are less likely to occur in certain situations because, in the past, those behaviors have produced unfavorable outcomes (punishers) in those situations.

In the 20th century, Skinner was the most notable champion of such selectionist principles as the basic mechanism of learning, but he was by no means the only psychologist to suggest as much. For example, at the turn of the 20th century, one of the most famous and influential psychologists of all time, Edward L. Thorndike, was conducting his famous research on animal intelligence that resulted in his formulation of the Law of Effect—one of the very few "laws" in psychology.  Thorndike placed  hungry cats in a handmade wooden "puzzle box," with a dish of food placed outside and in view.  The  boxes differed from one to another, but all had some way that the cat could open the box and escape, such as a lever that opened a door when pressed.  Thorndike observed that, at first, the cats took quite a while to accidentally make the response that opened the box, essentially stumbling on the right solution by trial-and-error.  After a cat finally did escape, it was placed back in the box and process was repeated many times, across many days.  Over time, and as a result of their experiences, the cats were quicker and quicker to escape, ultimately pressing the lever as soon as they were put into the box.

E. L. Thorndike's "Puzzle Boxes"
Image Source: Yale University Archives
This work is transparently selectionist, insofar as Thorndike reported an ever-decreasing range of behaviors exhibited by the cats as they were repeatedly exposed to the puzzle box.  Over time, the wide range of behavior originally seen (e.g., scratching, sniffing, whining) narrowed so as to be dominated by the lever press, which most reliably opened the box and resulted in escape and access to food.  In this case, the selecting aspect of the environment for the behavior of the hungry cat was escape from the box and access to the food.  This beneficial outcome selected lever pressing as the dominant behavior, while other varieties of behavior went extinct because they were not beneficial under these circumstances.  The cats still did all those other things (e.g., scratching, sniffing, whining), but not when they were in the puzzle box.

In the decades following Thorndike’s work, other psychologists arrived at similar conclusions about the importance of environmental selection as a causal mechanism of learning.  Again, in the language of Skinner’s operant conditioning, those events that follow behavior and result in the behavior occurring more often in the future under similar conditions are called reinforcers; the increase in future behavior is the result of reinforcement. In short, reinforcement selects behavioral characteristics of the individual in much the same way survival selects other (e.g., physical) characteristics of a species.

A chief benefit of learning over natural selection is that when environment change rapidly, the individual can change, too.  With both Darwinian and Skinnerian evolution, a selected characteristic is beneficial only in environments similar in some critical ways to the environment prevailing at the time of selection.  At the Darwinian level, a heightened sensitivity to fatty foods as reinforcers serves the species well in times when fats are in short supply, because we need fat in our diets to survive.  Across many generations living under such conditions, the numbers game favors those individuals most motivated to seek out and eat fatty foods, as they are the most likely to survive long enough to reproduce.  Should conditions change (as they most certainly have) with respect to the availability of fatty foods, this sensitivity to fat as a reinforcer loses its adaptive value and can even become a hindrance.  However, it can take quite a long time for evolution to fix the problem, which is where learning steps in.

Of course, learning requires, at the very least, a behaving organism that is the product of natural selection.  Even more than this can be granted to evolution, however.  Our genes influence our sensitivity to certain aspects of our environment and thereby play a crucial role in determining the extent to which those things influence our behavior.  In this way, our evolutionary past most certainly plays a role in determining our behavior, but not in any direct way, at least in most circumstances.

(The role of genes is undoubtedly even more pervasive in some circumstances.  The presence of seemingly innate aggressive responding to painful or otherwise aversive stimulation has been documented in non-humans and has led many to conclude that the same might hold true for humans.  Though the jury is still out, the claim is not entirely unfounded nor is it especially improbable.)

It is obvious that our genes play a crucial role in the ability of the organism to learn and perform certain behaviors, but the genetic role is one of proximate causation driven by the environment as the ultimate source of causation.  Even our genes are changed as a result of our experiences.  To quote science journalist Sharon Begley, "Evolution indeed sculpted the human brain. But it worked in malleable plastic, not stone, bequeathing us flexible minds that can take stock of the world and adapt to it."

We have inherited an ability to learn from our experiences, because doing so allows us to survive in an ever-changing world.