There is a long standing debate in psychology and medicine regarding what defines our physical traits (e.g., height), skills (e.g., memory) and personality (e.g., temperament). Which is more important genes or environment? We usually think of the impact of this question for early experience. Do we place emphasis on genes (nature) or on parenting/schooling (nurture)?

The most hotly debated topic in this arena is intelligence. Is intelligence inherited or is intelligence built from experience? Research estimates for heritability of intelligence range from 40% to 80% depending on factors such as socioeconomic class, age, and design of study. In other words, intelligence is determined by the interaction of genes and environment. Both are important. The practical implication of this is that ability is not fixed but rather is modifiable within limits. Early interventions (e.g., quality of teaching, decrease class size, memory training) with children and young adults can raise intellectual ability and performance.

We also need to keep this interaction between genetics and environment in mind as we age. There is such a sense of hopelessness about treating Alzheimer’s disease. I often hear professional as well as lay persons say “I don’t want to know as there’s nothing that can be done.” Fortunately, we don’t take the same approach to education. The overall heritability of late onset Alzheimer’s disease is about 50% (67% for identical twins and 22% for siblings). Genetics is not destiny.

We are so focused on genetics and microbiology that we often lose sight of the nurture side of the equation. Take for example the search for biomarkers (e.g., blood tests, cerebrospinal fluid analysis, and brain imaging) to detect Alzheimer’s disease. We treat cognitive (e.g., memory tests) and functional measures (e.g., adaptive skills) as if they are less important than the underlying biology. The interaction of genetic and environmental history determines function. Both are important. No matter what the biology, function and adaptive skills dictate which actual treatments (nurture) will be helpful.

Furthermore, it is becoming increasingly clear that cognitive and functional assessments out perform biomarkers in predicting and treating Alzheimer’s and related diseases (Archives of General Psychiatry, 2011, 68, 961-969). The most important determinant of how well you can live and how independent you can be is the ways your brain functions. What are the strengths and weaknesses in your ability? How can you use your strengths to compensate for your weaknesses? These are the questions addressed by neuropsychological evaluations.

Treatment for Alzheimer’s disease is built around assessment just as are educational programs. IQ scores (genetics) do not fully determine how well you will do in the education system or how well you will live life. Your adaptive skills determine how you will do as you age. Neuropsychological evaluations are best used to direct life plans as we age and to help us focus on the nurturing and adjusting skills as we age.