Double Helix

How can you possible think that way?

Dave Kinnear 1-On Leadership

I’m told that when it comes to the question of Nature versus Nurture and personality, the science world believes the debate is over.(i) The “Blank Slate” hypothesis is debunked. The consensus is that BOTH Nature (how our genetics wires our brains) and Nurture (the environment in which we are raised) shapes our personalities and pretty much our whole world outlook. And I find the statistics around these assertions very interesting.

Heritability is an important part of the studies that defines that part of the characteristic which is determined by the genes. Interestingly, 99% of our genes are shared (in common) with other human beings. So only 1% of our genes account for the individualism we all claim and of which we are often so proud. When we are looking at personality and attitudinal characteristics, we find that by studying monozygotic twins, dizygotic twins and siblings we can determine the range of heritability. For example, if we look at something such as “stubbornness,” we might say that if something has a heritability of “1” then Genetics plays 100% responsibility for that characteristics and environment has no effect.

So here’s a simple chart depicting the concept:

Characteristic Heritability Genetic Contribution









This tells us that if the “heritability of a trait is discovered to be “1,” then anyone and everyone who exhibits the trait of being stubborn has an identifiable gene or set of genes we could call the “stubborn gene” present. And the genetic contribution to the trait stubborn would be 100%. If the “stubborn gene” is determined to be only a .2 statistically, then the genetic contribution to the characteristic of being stubborn would be only 20%. Of course, all of this is very complicated in reality and will undoubtedly be refined as more data and research is gathered on the human population in general and twin studies in particular.

What I find interesting about all of these studies is how many characteristics we have found where we can measure a range of heritability. For example, in the U.S.A. a person’s height heritability is, on average, .87. That is to say, our height is 87% determined by genetics and the remaining 13% is determined by other factors. Of course, it makes a great deal of difference which group we are measuring. Height is only 62% heritable in Nigeria. Why? Because in the U.S.A., few people cannot get the necessary nutrition to reach their full height potential whereas in Nigeria many cannot, so their environment greatly affects this characteristic. In the U.S.A. marriage is .68 heritable and divorce is between .3 and .4 heritable.

Mental health factors are also heritable. Extroversion is approximately 50% heritable. Neuroticism has a heritability range of .3 to .5. And our attitudes and values are strongly heritable as well. But if this is all true, how do we account for the difference between siblings who we all know can be vastly different despite being raised in the same family and sharing the same genetic makeup? After all, they share 99% of their genes with their parents, just as they share 99% with all humans. And, they got about half of those genes from their mother and half from their father. And 1% of their genes are different which accounts for the siblings’ individuality. How does that work? Well, it is far more complicated than I can share here, but suffice it to say that genes can combine in different ways. So the sibling’s alleles(ii) are different. Yet there overall genetic makeup is 99% common.

As I mentioned, attitudes and values are strongly heritable. Whether or not a person is “conservative” or “liberal” has about a .59 heritability. Studies were made on the following traits:

• Tolerant
• Practical
• Orderly & Organized
• Stubborn
• Open to new experiences
• Easily threatened

You can decide if those are liberal or conservative traits. The point is they are shown to have a .59 heritability. In other words, the “reason” people who exhibit those traits have them is almost 60% due to genetically inherited brain organization. Their brains are “wired” to be that way and there is little hope that they will be able to fully embrace a different outlook. This is true for each of us. We are more at the mercy of our genes and our brain’s wiring than we would like to admit.

All of this learning has given me a big dose of humility. I will now remember that my own view is not really so much my own – it’s about 60% product of my genes and my created environment. In general, our genetic make-up also influences the environment we create for ourselves. Few of us go out of our way to live in an environment which takes us out of our comfort zone. Instead, we seek a “confirming” environment.

And my friends who do have an adamant and opposite view, well, it’s not their fault either. I get that I will not likely be able to convince someone to embrace a different world view. I now more fully understand why, even with well thought out arguments, others have not often been able to convince me that my world view is “wrong.” The best I can do is remember that (a) it’s not my fault and (b) it’s not their fault either. It mostly is just the way we’re wired. We can overcome some of that wiring because the brain is amazingly plastic. However, only to a certain extent can we change fundamental organization of the brain and only with difficulty. For now, I am going to endeavor to not be so “hard over” on my opinions on what is right, wrong, real and unreal. I’m already feeling stressed!

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(i.) Understanding the Mysteries of Human Behavior, Professor Mark Leary, Ph.D. University of Florida,
Duke University Ph.D.

(ii) An allele is an alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome. These DNA codings determine distinct traits that can be passed on from parents to offspring. The process by which alleles are transmitted was discovered by Gregor Mendel and formulated in what is known as Mendel’s law of segregation.