Genetics vs. Environment


“I have always been interested in genetics,” I said to 3-time Olympic Marathon Trials qualifier Susan Loken this morning as we were running together along the San Diego harbor. I knew before we started running that I was going to be pulled faster than I usually go. I could only hope that the 17-mile run I had on her training schedule yesterday, which she completed at 7:37 pace, would take the sting out of her legs. It didn’t. So I let her do most of the talking today so she wouldn’t know that her coach, who is 10 years her junior, was breathing heavier than usual for what was supposed to be an easy run.


Ever since I was a kid running track at Marlboro Middle School in New Jersey, I noticed things about athletic performance.

Susan Loken can kick my ass in a marathon. Despite her age, she has a talent for aerobic endurance that most people don’t have. But I would kick her ass in a 400-meter, 800-meter, or mile race. I have always had better anaerobic than aerobic qualities.

Athletic performance, of course, isn’t the only thing influenced by genetics. But what about personality, what about the choices we make and what is controlling those choices? How far do genetics go?

On the drive home from my run with Susan, I listened to a collection of TED talks on the genetics of our personalities and if the choices we make and the lives we live are controlled by those genetics. The geneticists claim that we are 100% our DNA (our genotype), and that our genetic personality dictates every choice we make, that there really is no such thing as free will. The epigeneticists claim that our personalities are partly due to our DNA and partly due to our environment that changes how our DNA is expressed (our phenotype). The research does show that DNA is not set, but rather that there is plasticity to our DNA. Environment does matter in shaping who we are.

But what if it doesn’t?

In one of the talks, a scientist spoke of the research that examined the behavior of mother rats and how baby rats that were licked by their mother (a sign of love and affection) thrived as adults and led different lives than rats who were not shown this affection by their mothers. To answer whether or not the way the baby rats turned out as adults was a genetic or environmental difference, the scientists separated rats at birth and had half the litter grow up with affectionate, licking mothers and half with non-affectionate, non-licking mothers. And they found that it wasn’t important the genes the rats got from their mother. What was important was the affection they received, that this affection can reprogram “bad” DNA and allow the rats to thrive as adults. Environment matters. We all know how important it is for parents to show affection toward their children, that the environment we grow up in affects our adult lives.

But, wait.

What if our environment is the way it is because of the genetics of the people who make up that environment? For example, what if the mother rats who didn’t lick their offspring didn’t do so because they didn’t have loving, affectionate genes? What if human parents who neglect their children or parents who show affection make that choice because that is who they are genetically? Is this an environmental difference or a genetic difference?

Do you and I make choices because we have the will to live how we want, or do we make choices based on our preferences and personality strengths and weaknesses that are dictated by our genes? To have that conversation while I’m running, I need to run with someone who won’t keep me out of breath.

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