We have all seen children who are different from one or both of their parents. We know people who are happy and buoyant; others tend to be depressed, shy, or anxious. Some persons go on to do very well in life and in career while others end up as suicides, in jail, or marginal at best. Why human beings do what they do is a fascinating phenomenon that people speculate about all the time. Even something as apparently clear and simple as height is in fact, complex. When it comes to explaining human behavior, we would do well to look to psychology – originally “the study of the soul” to discover explanations that are based in science. The results are interesting indeed. In this blog, I present a brief summary of what behavior genetics can elucidate about you, me, and all the rest.
A few paragraphs of caveats before I put flesh and sinew on these bones. Ideally, this scientifically-guided attempt at explaining human behavior doesn’t negate choice, free will, or personal responsibility. I don’t think it obviates the necessity of choosing our path multiple times a week – even daily at times. Recognizing our genetic substrate and the habits which our earlier years helped to create does involve certain limits. We can do much, but the entire world is not our oyster, as it were. We all get help whenever we create something significant, or achieve something wonderful. Think of the way a bird has certain abilities, limits, and ranges; a crow is smarter than a finch; a magpie can probably experience some amount of self-reflection; a dolphin can plan and adapt; an elephant can do things a mouse cannot. Can a flea be trained? Yes, apparently it can. Could a chimpanzee conduct sophisticated social relationships and act with surprising ingenuity? Indeed. But a chimp can’t speak, a bird can’t swim, and a dog can’t reason beyond certain limits.
My point is that freedom of choice operates in humans to a large degree, but it is constrained. Some of us are simply not going to be scientists or musicians. Humans even have a harder time picking up a new language once the childhood window closes. Like water running down a huge slope of Jell-O, our lives tend to find a particular path (though I am not saying we are necessarily meant to) and we proceed more or less unthinkingly. Yes, genes can be overruled to some degree (epigenetics) and obviously the whole point of psychiatry and psychotherapy are to help one overcome past experiences that helped to create a habitual way of thinking, believing, and behaving. Philosophy obviously helps us to believe that we can change, that we can excel, that the possibilities are still open. Psychology tells us that much is possible, but much drag is created by our past and our constitution.
I also do not want to downplay the role that luck (for good or ill) plays in a person’s life. “The slings and arrows of outrageous fortune,” as Shakespeare put it. I admit that there is a strain of thought, as heralded by Emerson’s famous ““Shallow men believe in luck. Strong men believe in cause and effect,” that we should make our own luck and such. I think it holds water to some degree. “Fortune favors the bold,” as Terence famously wrote long ago. Benjamin Franklin graced us with: “Diligence is the mother of good luck.” I get all that. I just think that often the reason we impugn the effect of luck is because it is the lucky – the winners – who promulgate such beliefs. Rarely do you hear the very successful thank luck for their touchdowns or appointment to the position of CEO; just as the victors write history, the notably successful credit hard work and talent for their achievements. “Well you can stake the claim/ Good work is the key to good fortune/ Winners take that credit/ Losers seldom take that blame,” lyricist Neil Peart pronounced.
Okay, back to the main thrust: what effect does human nature have on individuals? Behavior genetics is the branch of psychology that asks the degree to which behavior can be explained by genetics. A clarifying example is height. What percentage of height is based on genes? In other words, are you tall or short because your parents were and they passed their genes on to you? The answer is: depending on where you were born and grew up, your height ranges from very much based on genetics (e.g., America) to a bit more than half (e.g., the Sudan). Why? Persons in developing countries often want for nutrition, vaccinations, etc. and thus their growth can be stunted. Sad as it is, it illustrates that when it comes to explaining human behavior, optimal human development is either facilitated or stymied by our environment.
Evolutionary psychology is the branch of psychology devoted to trying to place modern-day behaviors in the context of human beings’ long past: that behaviors we engage in today are related to our evolutionary heritage. An example is: our fear of snakes is pretty pronounced even in America, not because they kill more than just a few people per year, but because in millions of years of evolution, snakes were a real threat and those human ancestors who were duly afraid of them were more likely to live to tell the tale. And, of course, procreate. We developed into a species who learned to fear predators and other dangerous situations. Thus, today we behave in certain ways because of our heritage. For example, we fear jumping out of airplanes but not really driving cars. However, thousands and thousands of people are killed every year by the human invention of the vehicle. We don’t have an intrinsic fear of driving because we don’t have an evolutionary heritage that selected for being fearful of traveling at 65 miles per hour. It is just too new in the scale of human development. We are literally using the same brain that our ancestors had in their crania when they were in the stone age.
You’re probably heard of the “nature-nurture debate.” It is the age-old attempt at explaining human behavior by trying to determine what part of who we are is based on things we inherit and things that happen to us once we are conceived. We are genetically programmed in a flash – the sperm combining with the egg. It takes decades to get to where we’re going. Did you know that the human brain isn’t fully developed until the late 20s? You read that right: teenagers have brains that are literally immature and underdeveloped. Not only do modern humans have a brain that belongs 100,000 years in the past, but until we are 25-30, we don’t even have a fully grown one! Thus it is no real surprise that 14-year-old boys get themselves in all kinds of trouble. This is an extremely fascinating story about adolescent elephants, which sort of illustrates the immature brain, but primarily, the role of culture and proper parenting in curbing a young (often, male) human’s baser instincts.
When it comes to genes determining psychology, it is fascinating to think that only 1% of DNA differs from person to person! That is, we are all 99% similar. In fact, we are over 98% similar to the bonobo. This is good news, since “Frequently referred to as the “Make Love, Not War” primate, bonobos have a reputation for being docile and diplomatic in their social and sexual relationships. Their generally peaceful and cooperative society is attributed to the evolution of a highly complex social system.” It’s terrible that we have allowed their habitat to be shrunken down to one country on Earth: the Congo. Happily, though, as long as we haven’t killed these cute creatures due to our greed and ignorance, we can study them, relate to them, and protect them – like a good older sibling should. But to get back to my point: take the shortest Caucasian you can think of and the tallest person of African heritage: they are 99% genetically identical. Tinkering with 1% of our DNA changes everything. It can account for a person turning out happy, ugly, fat, ambitious, tall, dark, short, light, blue-eyed, peaceful, or brown-eyed. Explaining human behavior is largely about our genes.
If that sounded wrong it’s because it was, to some degree. It’s not the whole story. Though genes account for 100% of our DNA (which commands certain outcomes and merely influences others), it is not truly determinative. For example, even with height in the U.S., genes only account for 80-90% of the variability (the range of differences). Thus, environment gets in there and makes a significant difference – even for height.
When it comes to explaining human behavior, intelligence is another human trait that is examined and fascinating. Trivia question: how important are genes in determining a person’s intelligence? Well, the fact that I.Q. tests are problematic in their validity aside, psychological science finds intelligence to be about 70% genetic. Here is a tidy little summary of the heritability of intelligence and a few other important concepts. Note that heritability seems to account for more of intelligence in higher socioeconomic status families. That is, the poor are not able to access their full potential because their environment gets in the way. It impedes growth and development, sad, though that is. Those Ayn Rand devotees would do well to consider that fact when they tout the will, autonomy, and destiny of the individual. Typically, they are thinking of the upper-SES individual. Explaining human behavior is a complex phenomenon, and we need to keep science in mind.
Personality is the main concern of this blog. Is an individual’s personality based mostly on genes, or everything else the experience – including, I hope, one’s free will. Psychologist Mark Leary sums it up in his informative and enlightening series Mysteries of Human Behavior: “Personality is certainly influenced by what happens to people – how they’re raised, what they learn, their personal experiences – but personality is undoubtedly influenced by people’s inborn, biological makeup. The nature-nurture debate is really dead; both nature and nurture – that is, both genetic and environmental influences – play a role in how people turn out.” As a general rule, personality traits such as extraversion, neuroticism, openness to experience, agreeableness, and conscientiousness are found to be 20-60% due to genetic contributions. Not a lot.
Values is always a common denominator in my writings. Mark Leary has an interesting thing to say on this topic: “One of the biggest surprises in behavioral genetics was the discovery that attitudes and values also have genetic underpinnings. Traditionally, psychologists have assumed that values and character traits – such as integrity and compassion – are instilled by parents and teachers and religions. And they are – in part. But there are also genetic influences. For example, researchers estimate that conservative, traditional attitudes and values [e.g.,] the death penalty, gay marriage, and censorship) …has about [a] 60%…genetic component.” Wow!
When it comes to explaining human behavior, consider the interesting case of President Jimmy Carter and his brother. Genes, environment, life experiences, and human choice play a role in how a person turns out, and few cases are more interesting than the Carter brothers. Jimmy went on to become an extremely accomplished individual, and his brother was pretty much the opposite. As Leary puts it: “We are often surprised when two children from the same family turn out very differently. After all, if two people have the same biological parents, grow up together in the same home, live in the same town, go to the same schools, and have many of the same experiences, we might expect them to turn out pretty similarly.”
Leary notes that Jimmy graduated from the U.S. Naval Academy – in the top 10% – owned a thriving business, got elected to many offices (including the presidency) and afterwards went on to become a real humanitarian and gave of his time to peace efforts, causes such as human rights, Habitat for Humanity, and so on. He is, pretty much by all account, a person who lived a good life and went about as far as a person can. His brother, Billy, however, was significantly different. He notes that Billy didn’t finish college, though he did own his own gas station. That might have been his apex, though, because he also was a beer spokesperson, a failed mayoral candidate, and was arrested for urinating in public (an airport runway). Billy was a nice enough guy, and Leary isn’t trying to impugn him, but he is “simply saying that Billy and Jimmy were so different that it’s hard to understand how they can be brothers from the same family who grew up in the same town under similar circumstances.”
I would note that luck and decisions play a major role in a person’s life. In explaining human behavior, genes provide a basis, but we are only about 50% related to each of our parents (and each of our siblings). Further, since only about 1% of genes differs from person to person, it sort of only provides a trajectory from which our environment and other factors can easily cause one to deviate. I think of genes like a bullet being fired from a gun: the original trajectory has a lot to do with the exact orientation of the barrel as the bullet leaves (and the condition of the interior of the barrel, in fact), but wind, gravity, the Earth spinning, and so on (not to mention a brick wall) make a difference in how the bullet travels. Jimmy Carter’s bullet was born under a fortunate sign, as it were, and traveled far and impressively. Billy was fairly genetically different from his brother, and had many different experiences. The day he decided that peeing in public was a good decision tweaked his trajectory for sure.
In sum, each of us can look back and see how we made decisions that led us to where we are at the present moment. For better or for worse, we chose A or B (or A, B, C, D, E, or F) countless times. Why we decided the way we did has a lot to do with our personalities, which are more or less only half based on our genetic heritage. When it comes to explaining human behavior, much is environmental (where we were raised, who our parents were and what they were up against in those early years, what the family social class was, factors like our race and religion and larger cultural milieu). For example, being Jewish in 1930 or 1950 was not as easy as it is to be Jewish in modern-day Los Angeles, New York, or Florida. Muslims, transgendered individuals, atheists, political liberals/icoloclasts, the obese, the poor, and the physically ugly have it harder nowadays than others do. Even being gay has become less of a significant event depending on where one lives in the 21st century.
We are all fascinatingly complex, and psychology, including behavior genetics, helps us explain how we became who we are, and puts some notable ranges on where we are capable of going. Our genes and early environment are primarily set and out of our control; the rest is up to us. Going forward, what can we do? I believe the best answer is that we can understand and live our values. Do what you are uniquely endowed to do, do it well, and try to be of some help to others along the way. Don’t do harm to life and don’t contribute to community- or planet-wide problems. Live a life of value.
Here is a podcast named “Our Constitution and Development” I did on this topic. I speak with Nancy Segal, Ph.D. Dr. Segal is an expert on behavior genetics and a scholar dedicated to the method of studying identical and fraternal twins to when it comes to explaining human behavior. Her research is fascinating and sheds light on which aspects of development are open to alteration, free will, and change. I had the pleasure of taking a graduate-level course with her on just this topic. Here is her bio.
