Nature and Nurture

In my last post I gave a brief description of one of the key mechanisms that Charles Darwin proposed drove the evolutionary process – natural selection. To recap briefly, natural selection is the preservation of phenotypes that are advantageous to individual organisms in what Darwin termed the “struggle for existence” amongst organisms. I noted that phenotypes can be any of an organism’s observable characteristics – some feature of its anatomy, physiology or behaviour. Selection for behaviours is the realm of evolutionary psychology. Generally speaking, evolutionary psychology refers to any attempt to apply evolutionary theory to the study of psychology. However, over the last 20 years or so, the term evolutionary psychology has become synonymous with a particular set of theoretical assumptions put forward by a group of researchers, the most prominent of who include the anthropologist John Tooby and the psychologists Leda Cosmides and David Buss (Buller, 2005). I’ll go into a bit more detail about these theoretical assumptions a little later.

I also noted in my description of natural selection that there must be genes at least partially responsible for each of the variant phenotypes, which parents transmit to their offspring during reproduction. It has been demonstrated quite conclusively in countless studies that genes, as well as experience, make a contribution to our behaviour and our cognition, or mental processing. This makes perfect sense because genes help determine the structure and function of the brain. One simply needs to open any introductory level psychology textbook to see that this is the case. For example, children of one or both parents with schizophrenia, a devastating psychiatric disorder that may involve disturbances in thinking (delusions), perception (hallucinations), emotions and behaviour, are at greater risk of developing the disorder themselves than children of non-affected parents. This is true even in cases where the children have been adopted at birth and raised by non-affected adoptive parents, so genes probably play some role in the increased risk for developing the disorder (Nairne, 2006).

Notice that I stressed the point that experience, or environmental factors also make a contribution. I do not want the idea that genes make a contribution to our behaviour and cognition to be confused with genetic determinism, the idea that these traits are determined entirely by genetics. The environment will always play some role!

In my last post I suggested that humans have a strong tendency to develop a fear of snakes. This does not mean, of course, that all humans have a fear of snakes. When discussing the causes of specific phobias (irrational fear of a specific object or situation), Barlow & Durand (2002) note that several things have to occur for a person to develop a phobia. While there is evidence that our brains seem to be “pre-wired” by our genes to associate fear with certain objects and situations, such as snakes and spiders (that is, we seem to be able to make the association more easily than say with live electrical wires, which are also potentially dangerous - see Footnote below), some kind of traumatic conditioning (or learning) experience is still generally necessary. This experience need not be a direct traumatic encounter with a snake or spider, but could also involve observing someone else experiencing severe fear in response to a snake or spider, or even, in some circumstances, being told about a potential threat. If the "purpose" of fear is to increase the chances of survival by avoiding certain objects or situations it makes sense that this emotion can develop without needing to face any danger directly. For example, a child who has a mother who becomes extremely anxious whenever she sees a spider may themselves develop an anxiety around spiders. Barlow & Durand (2002) mention a case of a woman with a severe snake phobia who had never encountered a snake in her life but had been warned repeatedly when growing up about the danger of snakes in high grass. She was encouraged to wear high rubber boots to guard against the threat – and did so even when walking down the street.

Another "risk factor" for the development of a phobia is the tendency to get anxious about future contact with the feared object or future occurrence of the feared situation (Barlow & Durand, 2002). Such a tendency would more than likely be the result of genetic and early environmental influences combining to produce an anxious, or neurotic, character. While not all fear may be considered irrational or interfere with an individual’s ability to live a normal life, and therefore be considered a phobia, Barlow and Durand's (2002) model gives us a sense of how experience and genetics/biology can both contribute to the development of behaviour and cognition.

Footnote: This is an interesting point and will be touched upon again when I discuss the theoretical assumptions that dominate the field of evolutionary psychology.

References

Barlow, D. H., & Durand, V. M. (2002). Abnormal psychology: An integrative approach (3rd ed.). Belmont, CA: Wadsworth.

Buller, D. J. (2005). Adapting minds: Evolutionary psychology and the persistent quest for human nature. Cambridge, MA: MIT Press.

Nairne, J. S. (2006). Psychology: The adaptive mind (4th ed.). Belmont, CA: Thomson Wadsworth.