Vol. 199 September 15, 2018 Nature vs. Nurture . . . an update

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“The closer scientists get to understanding the impact of individual genes,
the smaller that impact seems to be.”
– Evan Horowitz, Boston Globe, 9/11/18,C1

The discussion about what influences our upbringing the most, the environment (“nurture”) or our genes (“nature”), has been going on for decades. Sets of twins, particularly comparison of fraternal twins (two genetically different people born at the same time) and identical twins (two genetically identical people born at the same time), have been the subjects of much research trying to tease out the answer to which has the most influence. Why is one twin smarter than the other? Why does one love football and the other the violin? Why do they have the same walk, the same tastes in clothing, and the same gestures, but one has no sense of humor and the other is the class clown?

Despite the revelations in the recent movie, “Three Identical Strangers, many ethical and scientifically-rigorous twin studies have added a great deal of insight into the nature vs. nurture conundrum, and the discussion continues in the absence of consensus. The completion of the human genome project in 2003 was heralded as an historic step in finally settling this question. The hope was that, at last, we would be able to correlate a specific gene, or maybe just two or three genes, with a human characteristic, a human condition, and even a human disease.

In a recent study of the human genome, researchers found 1,271 different genes that seemed to improve educational outcomes. However, the cumulative effect of these educationally significant genes explained only about 11-13% of real world, actual educational attainment. (1) In a separate study by other researchers, the role of inherited genes in height, obesity, and education seemed to have much less influence than previously estimated . . . and a drastically much smaller role than suggested by twin studies. The influence of genes was highest for height (55%) and lowest for years of schooling (17%). The gene effect on cholesterol level was about 31% and the gene effect on determining your body mass index (BMI) was 29%.(2) There is no single “fat gene.”

One group of researchers suggested that perhaps the genes of the parents that are NOT passed to their offspring are important. What if the parents’ genes made them “slightly more attentive to kids and more willing to sacrifice their own happiness for the benefit of the kids”? Perhaps that could result in those children receiving a richer education. They suggested calling this influence of the parents’ genes on the children’s environment “genetic nurture”. (Thanks a lot for mudding the waters some more!)

There is no doubt that the genes we inherit from our parents influence our health and longevity. The adage, “To enjoy a long life, pick your parents right”, was dramatically brought home to me one day in the hospital cafeteria many years ago. A dozen of us physicians were discussing over lunch the pros and cons of a new study that daily baby aspirin could prevent some heart attacks, and different opinions about this brand new data were being voiced. A cardiologist espousing the strong genetic influence on heart disease interrupted our lively discussion with the question, “How many of you can call your father on the phone right now?” Only three could.

So the discussion of nature vs. nurture continues despite our growing knowledge of the human genome, but we have nothing to worry about as long as we have picked our parents right.

References
1. Nature Genetics, July 2018, as reported in Boston Globe, September 11, 2018
2. Ibid

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