Science often focuses on a part of nature, isolating that part, then describing and probing it. This is called reductionism. Although the approach can provide powerful insights, it can also cause scientists to lose sight of the context or surroundings, which are intimately connected to the part being studied. A plant or animal in a flask or growth chamber is no longer subject to the light and temperature changes of day and night, the seasons, rain and wind, predation, or disease.
I spent almost four decades in one of the most reductionist of all sciences, genetics. This field of biology started gaining popularity in 1900, when the laws of heredity determining the behaviour of genes and chromosomes were discovered. The science hasn't been without controversy. It has been used to argue the "nature" side in the "nature versus nurture" debate, and it has led some to claim a genetic basis for everything from homosexuality, social class, and IQ to criminality, mental illness, and a range of diseases. With its focus on genetic causes for illness, the science has also to some extent absolved government, industry, and health professionals of their responsibility to limit possible environmental and social contributors to disease.
Still, it has been an exciting and promising field. With the acquisition of immense powers to extract, analyze, and synthesize genetic material, or DNA, scientists embarked on an awesome quest to determine the exact sequence of all three billion letters of the genetic code in a human genome. When I graduated with a PhD in genetics in 1961, I never dreamed that we would acquire such capabilities within my lifetime, yet by 2001, the Human Genome Project was complete.
Billions of dollars were spent to map the human genome because scientists hoped to find the genes responsible for diseases like cancer, heart disease, and stroke. This knowledge, they thought, would allow them to design specific drugs and maybe even find a way to replace defective genes. For decades, we assumed that the Human Genome Project would reveal a hereditary basis for most diseases, just as they had been found for phenylketonuria, Huntington's chorea, Duchenne muscular dystrophy, sickle cell anemia, and cystic fibrosis.
The first surprise of the project was the relatively small number of genes found in humans. After all, we are complex animals and researchers assumed our position at the top of the evolutionary ladder would be reflected in a greater number of genes than "lower" animals. Instead, scientists found that we have fewer than many other animal and plant species, and we share at least 95 per cent with our nearest relatives, chimpanzees. We now assume the number of genes isn't what distinguishes higher forms but the timing of gene actions and interactions.
Armed with the entire sequence of genes, scientists have also developed ways to compare genomes of groups carrying different diseases in the search for stretches of DNA that might be correlated with the conditions. This is referred to as genome-wide association, or GWA. According to Jonathan Latham and Allison Wilson of the Bioscience Resource Project, more than 700 studies examining over 80 different diseases have all come up with similar results. Comparisons involving heart disease, cancer, stroke, autoimmune diseases, obesity, autism, Parkinson's disease, depression, schizophrenia, and other common illnesses reveal that many genes may have a tiny influence but none can be considered the major factor underlying the condition.
This is a stunning revelation that some geneticists find difficult to accept because it means designer drugs and genetic engineering to target or replace a genetic defect are not the answers. Billions of dollars have been and are being spent on GWAs and the search for major genetic determinants of disease. It's time to accept the reality that they won't be found and that we must instead turn to the challenge of addressing the more important contributors to human disease: malnutrition, lack of exercise, and polluted air, water, and soil.
And, as Dr. Latham and Dr. Wilson argue, "The laying to rest of genetic determinism for disease ... raises the stakes by confronting policy-makers as never before with the fact that they have every opportunity, through promoting food labeling, taxing junk food, or funding unbiased research, to help their electorates make enormously positive lifestyle choices."