One of the largest studies on longevity (hoping to find a genetic explanation for how long we live) discovered that spouses, NOT RELATIVES, share more in common with regard to lifespan and risks of all-cause-mortality: https://www.genetics.org/content/210/3/1109
Species. Eye color. How much melanin your melanocytes produce. Sure. These are legit. There are quite a few high risk diseases which have a heritability component which has reliable research supporting it. But when we get into personality traits and lifestyle-caused disease, it’s really dicey trying to pin it all or even a fair margin on genetic heritability. Not only have most theories come up empty-handed on reproducibility, the attempts to reproduce outcomes have backfired. That is, the preponderance of evidence is in favor of “other than genetics” as causal.
A lot of people have wanted DNA to be the be-all end-all explanation for all of life. In part, because people have a simple framework of nature-vs-nurture, they can’t really wrap their heads around a third, fourth, fifth causal set of options. Really, epigenetics and bacteriology tell us a lot about human health and behavior. Which switches get flipped and how our symbionts signal us play a massive role. That’s a few parts nurture and a few parts nature, which of course is not the way people wanted to think about it.
Trying to boil anything down to nature versus nurture itself is a question-begging proposition that most people miss. These two things aren’t different or divergent. I’m reminded of a George Carlin bit where he destroys marketers who label foods as “natural”. He just eviscerates people who talk about “unnatural” ingredients. As he said, “EVERYTHING EXISTS WITHIN NATURE.” All that is in our universe is “natural”. It’s part of nature. Nurture is another way of talking about nature. Trying to pit them against each other is nonsense. The variable pieces of nature work hand-in-hand with the static framework of physical laws. There is no one or the other.
But that hasn’t stopped those who want everything to be an impossibility outcome dictated by genes. The MAOa gene is a perfect example of people confusing themselves about how to interpret genetics research. Many carriers have no aggressive tendencies. But since some stats show an increased likelihood, we want to extrapolate that forward to mean people are genetically determined to be aggressive, determined, or violent. Then the debate devolves into whether or not we should give these people a pass when they commit violent crime. After all, they were genetically predetermined to be bad, right? Others on the flip side think sentencing should be harsher, since we have to get rid of these deviants who could never be rehabilitated and brought back into society.
You can see where this is going. But we don’t even need to entertain this foolish debate, because no one has reproduced statistically significant MAOa research. And many authors have dismantled it altogether as an explanatory model:
Anything else behavior-wise we want to pin on genetics is fraught with danger too. It seeks to avoid personal responsibility. That very thought disempowers you. Now placebo is at play. And you make it true. Therefore, even if genetics were a true explanation of most personalities and behaviors, it wouldn’t make sense to believe in it. The belief is self-reinforcing.
But we don’t even need to worry about that. Because, so far, linking genes as the sole cause for personalities and behaviors is pseudoscience.