Nature vs. Nurture

What determines our personalities?



 

February 2011

I returned to Greece after a 7-year absence a little under a year ago. Since then, a question has been stuck into my head: what determines us as persons? Is it the genes, the environment, or both? Do we have some choice into what we choose to do in our lives?

The question popped into my head, having lived and worked in three different countries by now (Greece, United States, United Kingdom). Each of these 3 lives has felt independent from the other ones – different people, different jobs, and different environment. In each country I had different hobbies, each time discovering something new about myself.

In Greece (between 1998-2003) I discovered that I liked math and science, that I liked going to the movies, and that I needed love in my life. In the US (between 2003-2008) I discovered that I liked custom-build PCs, Richard Feynman, ethnic restaurants, travel, convertible cars, steakhouses and photography. In the UK (between 2008-2010) I further discovered that I liked spending time browsing in huge bookstores, having friends in the neighborhood to hang out with, and so on. Each time, with each new discovery, I was wondering whether these characteristics of my personality where innate or where imposed to me by the environment.

Then I joined the army in Greece for my 9-month obligatory military service. I started getting to know a large number of people from all walks of life, from 19 year old “kids” who haven’t even finished high school, to academics and people that have been working many years in the industry. At the same time, there were still in my mind the hundreds of people I have met abroad, observing how people from similar background behave in different environments. I kept wondering then: what is it, after all, that determines their personalities?

To look for the answers I decided to read Matt Ridley’s “Nature via Nurture”, where he examines exactly this question using modern science. It’s an amazing book, which summarizes beautifully the whole story, and helped me a lot in my quest.

The rest of the article provides some answers to the questions of Nature vs. Nurture. If you want a short answer (not recommending it), here it is: both the environment as well as our genes determine our personality, not in a deterministic way bur rather in a circular manner, strengthening each other rather than competing with each other. Within a certain society, genes matter most; between societies, the environment does.

The rest of the essay is longer than this simple answer, because not only do I need to explain the details of how the system works, but also to focus on the all-important question: which choices determine our lives most?



Nature and Nurture. Genes and the environment. I first need to quickly go over the basics.

Genes are the genetic information we carry inside our cells from earlier generations, in the form of the DNA molecule. Environment is any outside influence, such as family, friends, climate, society, country status, etc.

Then there is the notion of instincts. There are actions that we do independent of our environment, such as the need for water, the search for food, or sexual desires. What makes us human and distinguishes us from animals are the things we do beyond our instincts. Culture could very well be the opposite of instincts, encompassing notions such as art, music, cooking, civilization, language, etc.

My quest began from two simple observations about the Greeks. First, Greeks eat a lot of meat (2nd in the EU after Germany). I’ve never met a single vegetarian Greek living in Greece. Second, although I’ve met many atheists, in their vast majority Greeks are of Christian Orthodox religion. I wondered why.

The answer seems obvious here. It’s the environment! These properties (religion, food preferences) are determined via nurture and not via nature. Greeks just happen to grow up in an environment that already encourages eating lots of meat and where most people are already Christians. Had they been born in, say, an Islamic country, they would probably not eat as much meat (definitely not pork, which is the main ingredient in our souvlaki), and would also probably be Muslims. This is confirmed by Greeks that I know, who have been raised outside Greece – their food and religious preferences match each country’s own accepted norm. I myself started eating less meat and fully became an atheist as soon as I moved out of Greece.

As a second example, think of Chinese born in China versus Americans born Chinese. They all have similar genes, yet the result is completely different body types, food habits and cultural interests.

Thus I conclude that these people have not freely chosen these habits, they’ve rather just copied their environment. This is also why I have utmost respect for people who convert to being vegetarians and atheists, since they have willingly chosen their way of life by breaking free from the norms of western societies. These are the truly free. (Not that none of the rest are free – you just have to go through a process of consciously choosing your own preference rather than simply accept it).

These are just a couple of examples where nurture affects our choices. For the Greeks, there are a number of other items which, although they seem like conscious choices, are imposed from the environment: e.g. owing a small or midsize car (streets are narrow and salaries low), working as a state employee (better benefits compared to most private companies), or living in apartments (cities are too cramped to build houses). These are all pseudo-choices because they are imposed from the environment, sometimes due to being almost the only feasible options available.

What, then, is the role of genes in our life choices?

Richard Dawkins offers a great example for the role of genes. He says that genes are like recipe instructions, which, after baking, can make a great cake (that’s us). But looking at the final product (the cake), we cannot trace a specific section of the cake back to a specific word in the recipe. And the oven we bake the cake in is the effect of the environment. Similarly, our human genes are just instructions, and it’s rarely possible to trace a specific part of our body (or personality) back to a single gene.

Following this line of arguments we can also explain why we are so different from chimps although we share 98% of the same genes. Ridley suggests it’s like comparing two books; say Dan Brown’s “Angels & Demons” and Michael Herzfeld’s “Evicted from Eternity”. Both books talk about Rome, and they probably use like 90% of the same English words in them. Yet the outcome couldn’t be more different, the former book being a fictional novel and the latter a factual piece of writing. It’s the order and structure of the words that makes all the difference, not the words themselves. Same goes for genes: it’s their order and what they do that make the differences between people and species, not their explicit content.

As we shall see in a minute, these genes can be switched on and off by other genes or by the environment. This is how new properties, new personalities, and new habits can be accomplished via a fixed number of genes – not by introducing new genes, but by manipulating existing genes. And all this doesn’t need to be encoded in the genes only: the genes can be actively manipulated by nurture.



The following sentence is the most important in the whole essay:

Nature prevails over nurture in defining personality differences within the same society.

Let me explain. This means that within the same society (i.e. having more or less a constant environment), any differences between people can be attributed to the differences in their genes.

This is backed up by evidence acquired by studying twins (which have almost identical genes) in western societies. As you probably know, identical twins originate from the same egg (thus sharing almost the same genes), while fraternal twins originate from two different eggs in the womb (this is just like normal brothers, only born at the same time). The studies show that identical twins raised apart are much more similar to each other than fraternal twins raised apart. This is true both for personality as well as for more easily measured things like body weight.

Focusing on body weight, within the same family (i.e. keeping nurture constant) identical twins have 80% correlation in weight, while fraternal twins only have 43% correlation; the genes make all the difference. When the identical twins are raised apart (i.e. varying their nurture slightly), their correlation drops just to 73% from 80%, remaining essentially unchanged. Thus genes seem to matter more than family!

This correlation holds true as long as the environment does not dramatically change. If you are an orphan in Sudan, or a worker in the slums of India, it doesn’t matter what your genetic predisposition is – it is very likely that your body weight will be low, since the access to food might be scarce. In the identical twin studies, where twins are raised apart but in more or less the same society with same access to food, the remaining differences are bound to be genetic.

In a sense, family (via nurture) is then like vitamin C – lack of it makes you ill, but above a certain level it doesn’t cause any notable differences. For the parents that they want to shape their children’s personalities, the news is then mixed. Being a parent still matters, because you have to provide a certain level of quality of life to your kids, satisfying their basic needs (food, play, education, etc.). But after these needs are met, genes matter more: nature takes over from nurture.

Another great example for the effect of family comes from examining families with criminal parents. The fact is that criminal parents give birth to children that have statistically more chances to grow up and also become criminals. Is this because of specific genes? No! It’s just that some types of personalities are more likely to get in trouble, and these personalities are heritable. Supporting this argument, studies show that adopted children in criminal families do not become criminals at the same rate as biological children.

Let’s now examine schools. For a number of reasons, kids that attend a certain school are usually of similar financial background, same race, and same location. They also receive the same education. Hence, in most schools any differences in student scores can easily be attributed to their genes. Once again, the environment determines your average status, while the genes highlight the differences between individuals.

The more meritocratic a society is the more genes matter. In an ideal meritocracy, the people with the “best” genes would attend the top schools and would therefore land the top positions, since we do not allow any random influences from the environment. Inevitably, the stupid ones would be left behind. Would you then be willing to live in a society knowing that if you are born stupid (which you can’t control really), then you are doomed to fail because you won’t be given any chances?

What about intelligence? Intelligence has also been measured in various studies, through IQ tests in various socio-economic groups. It turns out that nurture can actively affect your IQ: people that have grown up in poor families, where the parents make e.g. $4K a year, have lower IQ scores than people from families where the parents make $40K a year. Interestingly, the latter score does not increase when comparing people from families that parents make $400K a year. Once again, nurture sets the average, and once a certain average is met, any further differences are due to nature.

But all is not over once nature takes over. Nature needs nurture to express itself. Say a boy has a natural talent, such as being good at football. He needs to be provided with the corresponding environment where he can enhance his skills through practice. Having sporty genes will make you seek athletic activities, which in turn will amplify your genetic predisposition towards football. On the contrary, another boy with more “intellectual” genes will tend to read more books, enhancing his intellectual skills and maybe suppressing his sporting skills. By the time the two boys reach adulthood, one will become a footballer and the other one a writer. But their destinies were defined by nurture acting on nature – a combination.

(Sometimes I like to compare nature and nurture with a Gaussian function, defined through its mean and standard deviation. Nurture sets the mean, while nature sets the standard deviation.)



Another example of the correlation between nature and nurture is homosexuality, which is usually regarded as a genetic predisposition. However, a “gay” gene has never been found. Why is that?

Studies on people that have older brothers show that for each extra older brother a person has, his probability of being gay rises by 1/3. Thus it’s more likely to be gay if you are not the first to occupy your mother’s womb. At the same time, the younger siblings who have older gay brothers weigh on average 170gr less at birth. It seems like the mother is having a certain reaction after the shock of the first birth, which results in subsequent babies to weigh less at birth. Based on this argument, your chances of becoming gay are increasing not genetically but totally through nurture – the environment you are grow up inside the womb. Thus we cannot pinpoint an isolated root cause of being gay to neither nature nor nurture.

(As a side note, Ridley in his book also suggests an interesting reason on why natural selection would favor gay descendants: because childless uncles would help their brothers raise their babies.)



We’ll now focus in one of the most interesting experiments in the history of the nature vs. nurture debate – Mineka’s monkeys and the fear of snakes from the 1980’s.

Mineka observed that monkeys are afraid of snakes, and believed that this fear is acquired by young monkeys when they are observing their parents’ reactions to them. Mineka threw snakes next to a baby monkey’s food, and allowed the baby monkey (which had never seen a snake before) to approach the food and see its reaction to the snakes. When the mother of the baby monkey was present in the scene, she quickly reacted violently to the presence of the snakes, by shouting, moving around quickly, and jumping, doing everything she could to warn her child. Indeed, the baby monkey quickly acquired the same reactions, and whenever the baby monkey saw snakes it was afraid to approach. The same results repeated even when it wasn’t the baby monkey’s parent but a stranger monkey to provide the warning instead.

However, when another monkey wasn’t present in the scene, the baby monkeys went straight to the food despite the snakes around. This showed that the fear of snakes wasn’t genetic per se, but learned via nurture, after observing someone else’s behavior.

The best part comes next. Mineka subsequently decided to see if she could induce a fear for another object, such as a flower, to the baby monkeys. She had already found that a real monkey wasn’t even necessary to provide the reactions of fear for snakes – the baby monkeys would acquire the fear of snakes even after watching a monkey reaction on a TV. So, she placed flowers next to the food, while the baby monkeys were shown reactions of fear on the TV – as if the other monkeys were warning them about the “dangerous” flowers. Surprisingly, the baby monkeys never acquired any fear of flowers though!

The latter experiment indicates that there is after all a genetic role in the fear of snakes, which is turned on via nurture – by acquiring the fear from the peers. This shows that there exist features in someone’s personality that can’t be attributed to neither nature nor nurture alone – it’s only their combination that has an effect.

In fact, it is interesting to notice that we as humans also have innate fears that we have been passed down in our genes from earlier generations. We are afraid of snakes, spiders, darkness, heights, deep waters, and thunder. These are all things that could kill you in the Stone Age, so it makes sense that any of our ancestors that survived them would have developed a fear about them – which would be passed on via their genes to protect the future generations. In contrast, we are not innately afraid today of many things that can kill us, such as cars, guns or electric sockets: these phobias are modern and we haven’t had enough time to incorporate them into our genes.

Thus an interesting way to view our genes is that they contain extracted information from the environments of our ancestors. We have experiences from our present environment every day as humans, and genes provide us with information about past environments via the genetic code, transforming our bodies and our personalities, in order to be better prepared to survive in our world.



So where does this leave us in the nature vs. nurture debate?

Well, there is no simple answer. First, the idea that single genes are responsible for single features of one’s personality is rarely true. It’s not the genes per se, but their order and combinations which matter most. And they can be affected either by nature and/or by nurture.

Second, nurture sets the stage upon which nature can play. Nurture matters most up until the basic human needs are met. But within a settled society, where the environment is more or less the same between people, the differences that arise originate mostly from nature.

Thus it seems to me that the only way we can have some serious control over our personality is by drastically changing the environment we live in. Trying to do the same things over and over within the same society won’t have any appreciable effect most of the time, because our genes would do most of the talking. People need to dramatically change environments, either by switching lifestyles, switching jobs (but totally different jobs), switching cities, or switching countries. And the more different those environments are, the more one would develop his or her personality: the nurture differences would result in affecting nature, turning on and off new genes, developing new characteristics.