The False Dichotomy Of the Nature-Nurture Debate

Every few months, scientific press releases with headlines more eye-catching than the British tabloids claim that the nature versus nurture debate has finally been solved. Indeed, judging by those press releases, it seems that the debate is being solved again and again . . . and again. But this becomes even more ludicrous when you come to realize that the nature versus nurture debate is no debate at all.

Nature and nurture can be represented by genes and the environment. Your genes come from your biological parents while the environment includes your physical, chemical, and biological exposures as well as your lifestyle factors. At first view, the two may seem like independent components which have isolated effects on particular diseases or traits — hence the notion of a debate. Said debate asks the question: What characteristics of your identity are due to nature (your genes) and due to nurture (the environment)?

As it turns out, most diseases or traits are each due to both genes and environment. Traynor and Singleton (2010) in their recent perspective in Neuron state that:

It has been quite convincingly argued that nearly all human diseases and physiological traits involve genetic and environmental influences to some extent.

In fact, they go on and describe nature and nurture as not being two independent components but as two intrinsically linked ones ("synergistic effect of genes and environment on a disease or trait") that make up the gene-environment interaction. The authors give some examples to showcase gene-environment interactions. And they are eye-openers.

The height of a person comes with a high heritability. If your biological parents are tall, you most likely will become tall too. However, when viewed on a population level, it has been shown that the average height of a population grows in concert with a nation's economic prosperity. It would seem that height is not exclusively genetically-determined after all but is also linked to improved nutrition.

A number of diseases such as diabetes, coronary heart diseases, and cancer have genetic and lifestyle links. A more balanced diet and regular exercising correlate with lower risks of coronary heart diseases, for instance. The discovery of tumor-inducing viruses in 1911 by Peyton Rous also show that environment can be a cause of diseases. However, those mentioned diseases all have genetic bases as well.

Perhaps most surprisingly is the notion that infectious diseases, the sine qua non of environment-based disorders, have a genetic component too. It is now understood that "infectious diseases are influenced by host-microorganism interactions, with the diversity of the immune system being rooted in genetics."

It is becoming ever more obvious that genes and environment are both involved in a disease or trait. Both nature and nurture are responsible for more or less each of your characteristics. As such, we should no longer draw a line between the two and list characteristics that are due to one and the other in two separate columns. Indeed, those two columns never existed in the first place.

However, merely saying that the debate doesn't exist and discarding it would mean missing a great opportunity to recalibrate our notion of nature and nurture. As Evelyn Fox Keller, author of the book The Mirage of a Space Between Nature and Nurture, reckons, the real issue is trying to understand what it is exactly that we can ask and can gain new knowledge about, what sorts of questions it makes sense to ask, versus which ones are in principle incoherent.¹

So, in the aftermath of this non-debate, what sorts of questions do makes sense to ask? As Lena explained in the previous post of this series, epigenetics may possibly be a focal point. While we are to some extent pre-programmed through our DNA, the different ways in which the DNA is expressed differs from person to person. And those different ways of expressing DNA is actually passed on from generation to generation. The seemingly simple question of how nature and nurture play roles in the way DNA is expressed leads to broader ones like, "What are the ranges of variation?" and "Under what circumstances can behavior or physiology be changed?"²

The nature versus nurture debate is no debate at all, son, but then again, that doesn't mean that the non-debate is of no use either.

Image Credit: OpenEye (from Flickr)

Reference:

Traynor BJ, & Singleton AB (2010). Nature versus nurture: death of a dogma, and the road ahead. Neuron, 68 (2), 196-200 PMID: 20955927

1. Keller, E.F. "Goodbye, Nature vs Nurture." New Scientist. September 20, 2010

2. Dizikes, P. "3 Questions: Evelyn Fox Keller on the nature-nurture debates." MIT News. November 30, 2010.