Our some 30,000 genes are our parents’ initial gift at conception—the set of instructions on how to construct and operate our body. It includes useful directions on such basic things as gender, body organization, skin/hair/eye color, and temperament. About nine months later our parents discover how their combined genetic directions turned out, and they’re usually pleased. We love our babies, who tend to resemble us, but who definitely depend on us to take care of them.

Thirty thousand genes are enough to direct the development and operation of a basic birth body, but they’re not enough to provide specific directions for living out our complex extended life. Parents must thus provide their child with a second set of instructions—how to transform genetic beginnings into a qualitative cultural life. Their child’s extended family, peers, schools, and mass media assist in this task.

The nature/nurture issue revolves around the relative levels of influence that genetic inheritance (nature) and our life experiences (nurture) play in determining our traits and capabilities—in effect, the person we become.

To simplify our complex biological inheritance system, a gene is the section of the long convoluted DNA molecule in every cell’s nucleus that prescribes the sequence of amino acids that make up a specific protein—and proteins define much of our physical self, since we’re basically a big sack of proteins. Genetics (nature) would thus certainly influence such protein-driven body properties as height and shape—but diet and exercise (nurture) can usually alter such basic genetic plans. Genes similarly regulate the development of brain structures, so such cognitive functions as movement, language, and memory also have a genetic base—but experience constantly alters the current organization of a brain’s networks and its synaptic connections.

Further, the nature/nurture issue has political overtones. Folks who believe that nurture is the primary influence in a person’s maturation and lifestyle strongly support social service and education programs, and especially those that help folks at the lower ends of various human attainment scales. They say in effect: Imagine a goal, strive towards it, and our society will help you to achieve it.

Folks who believe that nature is the primary influence in who we become are less inclined to support massive programs that hope to improve human conditions they feel can’t really be changed. They say in effect: Accept your abilities and limitations, and we’ll do our best to create a broad accepting society that can accommodate a wide range of capabilities and personalities.

What scientists now understand is that neither extreme position is correct. Some human properties such as height and skin color are genetically determined and almost impossible to change, but other properties such as the language we speak and the cultural rituals we follow are almost entirely based on experience.

Scientists use a measure called heritability that statistically estimates how much nature and nurture contribute to the individual variation observable in a trait. For example, are differences in susceptibility to an illness more related to family lineage or to environmental factors (such as diet or environmental pollutants)? Scientists compare the total amount of variation in susceptibility within a population with the level of susceptibility within specific families. If relatively few people in the general population are susceptible to the illness, but those within certain family groups are much more susceptible, the illness would be considered heritable.

On the other hand, if you are a member of a family of loggers, your chances of being injured in a logging accident are higher than in the general population, but that type of susceptibility wouldn’t be considered heritable. Fingerprint patterns are thus considered heritable, but calluses are occupational (or environmental).

If a trait is said to be 70% heritable, that doesn’t mean that 70% of the trait is due to genetics and 30% to the environment. Rather, it suggests that 70 % of the observed variation in that trait in a specific sample of people can be attributed to genetics and 30% to environmental factors.

Most people have difficulty understanding the subtle complexities of genetics, but we’re all increasingly being drawn into moral and political controversies over genetics-related issues. Indeed, Korean scientists have just announced the successful cloning of a human embryo. This development will certainly exacerbate an already contentious discussion of the cultural appropriateness of such research. The resolution of such issues in our democratic society will involve many voters and politicians who unfortunately don’t really understand the underlying science implicit in the decisions they’ll make.

In light of this societal need for knowledge, it’s reassuring to report the publication of two recent excellent books for general readers on the scientific base of genetics, and especially of the nature/nurture issue: Matt Ridley’s Nature Via Nurture (2003) and Gary Marcus’ The Birth of the Mind (2004).

Ridley provides a fine historical foundation for the issue, as he explains how genes enable rather than constrain behavior. Genes provide the mechanisms for biological possibility, but the challenges we confront and the decisions we make determine which genes are expressed to facilitate our responses. Ridley thus rejects the conventional nature versus nurture perspective, arguing persuasively and eloquently for a collaborative nature via nurture perspective.

Marcus focuses on the roles of nature and nurture in cognition. The issue he explores so well is how a relatively small number of genes can develop an incredibly complex common human brain that is also unique in each human being—flexibility within constraints. He uses many excellent illustrations to explain why and how our society must rethink its static conceptions of nature and nurture in order to truly understand our brain and cognition—and how this new understanding will advance medicine, education, and many other key elements of our culture.

Two excellent non-technical books on an emerging cultural issue that is as interesting as it is important.