Nature or nurture ????

For centuries, millennia even, people have debated whether human intelligence and behavior are the product of our biology or our experiences. The grand philosophical roots of this question are captured in the distinction between Descartes’ famous “erased slate” (tabula rasa), which argued that children are born with no knowledge, that they are empty slates, such that everything they are and do is learned; and Rousseau who described children as noble savages, born with basic knowledge and goodness that becomes misdirected by society. A very common view was that children are preformed miniature adults.

The argument was alive and well in the 20th-century. In mid-century, the famous behaviorist, B. F. Skinner, boasted that he could train any newborn to become anything wished — a surgeon, an artist, or whatever. Experience reigned supreme. A couple of decades later, data from twin studies began to come in and revealed some surprising similarities among identical twins who had been reared separately. The pendulum swung from nurture to nature. By the end of the century there was a greater sense that both were important and the heritability coefficient was introduced. It is a statistical technique for calculating the amount of a feature, such as height or intelligence or sociability, that can be attributed to heredity and the amount due to experiences. With the exception of a few physical characteristics such as height, heredity is generally thought to account for 50% or less of a feature. The range for different personality traits is 25 – 46 % (Pervin, 2003)

So when the new millennium opened, the nature ~ nurture question had resolved to something of a balance between the two. But now, even that seems simplistic. One reason has to do with the human genome.

Before the human genome was mapped in 2000, scientists believed there were about 100,000 human genes, each responsible for a single feature or trait. The stunning discovery is that we have less than 25,000 genes. Each gene produces a number of different proteins in response to signals from hormones, other genes, and various cells. Genes produce changes in their environment and the environment triggers changes in a way genes function and the kinds of proteins they produce. This revelation means the the relationship between nature and nurture is a very complex and dynamic one.

In a dynamic relationship the various components mutually influence one another in a continually changing way. That is what dynamic means; the system is in a constant state a flux. This is true at the cellular and all other levels. Very simply, it means that experience actually influences cells and genes, and also that cells and genes influence how each individual responds to experience.

A very important quality of a dynamic system, such as human development, is that the output is not fully predictable. In a simple system the results of an action are known can be predicted. If you add two atoms of oxygen to an atom of hydrogen you get water. That’s a simple system. In a complex system the results of an input depend on a complex interaction among the variables. If you add carbon dioxide to the atmosphere, its effect varies depending on temperature, wind factors, presence of other substances in the atmosphere and how these interact with carbon dioxide and so on.

Human development is an extremely complex dynamic system. What this means for us as parents is that what we do influences our children, but not always in fully predictable ways.

Here’s an example of how individual differences in children affect ways they respond to parents

A simple example illustrates this. The form of a particular gene, DRD4 7-repeat, is associated with attention problems, aggressiveness, and attention deficit hyperactivity disorder (ADHD). Studies show that providing sensitivity training to parents can increase a pre-schooler’s ability to regulate stress, as measured by changes in cortisol among children who carry this DRD4 7-repeat gene form (Bakermans-Kranenburg, et. al. 2008). Yet the measures of cortisol do not change in children without this genetic marker.

What this demonstrates, is that genetics can influence the way children respond to their parent’s actions.   Genes are not the only individual variant though.  Many other factors can influence how each individual child responds to input.

Research examining the intricate relationships among bio-genetic factors and external influences is still very new. What is clear however, is that it is no longer a question of nature or nurture. Both are extremely powerful and deeply interconnected. Genes provide a set of potentials, which experiences can enhance or diminish or alter.  They can also influence how an individual will respond to experiences.

How you can use this information

*  What parents do influences their child’s development. Yet, it is not fully predictable how a child will respond.
*  Each child brings his or her own qualities, traits, response patterns, gifts and challenges. Each of these alter as the child interacts with the world.
*  There is individual variation in how children respond, something parents with more than one child quickly come to recognize.
*  Part of a parent’s own development involves changing in response to his or her child.
*  Observing, being flexible, and noticing how your child responds to your actions can help you figure out the best ways to support and interact with your child.
*  You are important, but you are not responsible for everything.


Bakermans-Kranenburg, M. J., Van IJzendoorn, M. H., Pijlman, F. T., Mesman, J., Jufffer, F. (2008). Experimental evidence for differential susceptibility: dopamine D4 receptor polymorphism (DRD4 VNTR) moderates intervention effects on toddlers’ externalizing behavior in a randomized controlled trial. Developmental Psychology, 44, 293-300.

Pervin, L. (2003). The Science of Personality, 2nd Edition. New York: Oxford University Press