Over the years, we hear about "cancer clusters" or a growing rise in behavioral conditions like autism and advocates and families want answers. Is it our genes or something in the environment? This concern often leads to an epidemiological study that tracks these diseases over time. But sometimes, despite the time, effort and expense, no definitive causation is established. This can be frustrating to families facing these conditions and the scientists who are looking for answers. This is the conundrum of nature vs. nurture.
The problem is that the causes of particular diseases may be part of both. For example, it is not uncommon to have the explanation of a disease presented as 25% genetic (nature) and 75% environmental (nurture), adding up to 100% (like slices of a whole pie).
However, what we have learned from gene-disease association studies is that in reality, human disease is rarely a product of such simple and clearly defined relationship. Causation of human disease is not about nature OR nurture but more about nature AND nurture. Gene-environmental interactions underlie almost all human diseases. The Center for Disease control (CDC), explains this on a recent blog.
Most common diseases such as coronary heart disease, cancer, and diabetes are caused by modifiable environmental risk factors such as smoking, diet and lack of exercise. However, if you have a family history of one of these conditions, your risk will likely be higher than someone without a family history. Even though the human genome has been uncovered, we do not yet have the tools to quantify or even guess at the vast number of variations that can exist.
Rather than think about slices of pie, the CDC suggests we look at a different metaphor: vegetable stew! The genes are represented by the different combinations of vegetables used, and the environment can be the amount of time the stew is cooked, the temperature, what kind of pot was used (aluminum vs. cast iron). Taking this further, there are different varieties of corn, tomatoes, herbs and beans and the spices used can change the taste immensely. Once assembled, the ingredients blend and cook to produce a combined but unique flavor. Biologic processes function in a similar way, as genes respond to constantly changing environment.
As scientists continue to work with the human genome, there may come a day when we can learn more about our personal vegetable stew recipe.