What kind of person will you grow up to be?

A mother gazes lovingly at her newborn baby as he sleeps peacefully in his crib. Careful not to wake the infant, she gently whispers, "My son, what kind of life will you have? Will fortune smile on you or will you be dogged by bad luck? Will you enjoy good health or will you be sickly? Will you be happy or will you be miserable? Will you be liked or will you be hated? Will you live in times of peace or will you know the horrors of war? Will you be a law-abiding citizen or will you be a criminal? Will you find true love or will you be forever lonely? What kind of person will you grow up to be?"

This week I was taken aback by a small article in the newspaper which told of an old high-school classmate of mine (I'll call him Jim). Jim was recently sentenced to almost a year in prison for his dealings with the Melbourne underworld. I remember Jim as being a loud, boisterous kid who loved his football and who gave a lot of backchat to the teachers. Though he was well known as a tough guy, he was never a bully; he was the class clown who thrived on breaking all the rules. I haven't seen him in over 25 years but, over the years, I had occasionally heard rumours that he had become a wealthy businessman after he took the reins of his father's business. In my mind I pictured him driving a sports car, chomping on a fat cigar, and maybe laughing occasionally at the memory of all the teachers who thought he was no good, and ridiculing his nerdy classmates who got high marks. But it gives me no pleasure at all to know that he is now languishing in jail - his life in ruins. I hope he can bounce back.
At school, Jim and I didn't associate with each other; he was the confident loudmouth and I was the shy timid nerd-type. What determines these differences in temperament? What determines the kind of adult we are destined to become? Is it genetic or is it upbringing ... or is it a combination? How influential is our family upbringing? Is there any truth in the Jesuit saying, "Give me the child for the first seven years, and I'll give you the man"?
In the book "The Blank Slate", Steven Pinker lists the "3 laws of behavioural genetics":

* First Law: All human behavioral traits are heritable.
* Second Law: The effect of being raised in the same family is smaller than the effects of the genes.
* Third Law: A substantial portion of the variation in complex behavioral traits is not accounted for by the effects of genes or families.

Let's examine each of these laws:

First Law: All human behavioral traits are heritable.
By "traits" we mean things like general intelligence, proficiency in language, maths ..., shyness, conscientiousness, dependence on cigarettes or alcohol or gambling, antagonism, confidence, sports talent ... etc.
We know that identical twins share all their genes. It has been shown that identical twins reared together are more similar than fraternal twins reared together. We know that biological siblings are more similar than adoptive siblings. We know that identical twins reared apart (in different families) are very similar. Pinker does not suggest that the effect of genes is certain; even if a child is genetically suited to being a champion sprinter, he will not realise his potential if he never run and never trains. An analogy is the relationship between temperature and snow. There is a likelihood of snow at temperatures below 0 degrees Celsius, but it doesn't always snow at those temperatures. However, it never snows when the temperature is 20 degrees Celsius. It's the same with genes; as far as things like temperament and sports ability are concerned, environmental factors have an influence, but genes provide a bias. Genes affect the probability that the child will acquire a particular trait.

So does this mean that out children's destinies are shaped by a combination of genes and their family upbringing? This takes us to the second law - by far the most controversial (in fact, Pinker spends a few pages defending this law).

Second Law: The effect of being raised in the same family is smaller than the effects of the genes.
Pinker distinguishes between the two types of environment : the shared environment and the unique environment. The shared environment is what affects us and our siblings: that is, our parents, our home life and our neighbourhood. The unique environment is everything else - anything that affects one sibling but not the other - for example: parental favoritism, different experiences, accidents, illnesses, friends.
Experiments with identical twins have shown that the effects of shared environments are small - often statistically insignificant. It has been shown that siblings reared together end up no more similar than siblings separated at birth and adopted siblings are no more similar than strangers. But this second law is weakened by the following caveat that Pinker provides:

"The studies exclude cases of criminal neglect, physical and sexual abuse, and abandonment in a bleak orphanage, so they do not show that extreme cases fail to leave scars. Nor can they say anything about differences in cultures - about what makes a child a middle-class American as opposed to a Yanomamo warrior or a Tibetan monk or even a member of an urban street gang. In general, if a sample comes from a restricted range of homes, it may underestimate effects of homes across a wider range."

The studies were made on middle-class families which, as Pinker points out, embraces a wide range of lifestyles.

The third law is much less controversial - in fact, it makes perfect sense.

Third Law: A substantial portion of the variation in complex behavioral traits is not accounted for by the effects of genes or families.
It means that identical twins reared together - who share both their genes and a family environment - are not identical in their personalities. This must obviously be due to their respective unique environments. Even in the womb, identical twins may be subjected to slightly different conditions.

Pinker summarizes the three laws as follows: Genes 40-50 percent, shared environment 0-10 percent, and unique environment 50 percent.

The second law is the most problematic because it implies that parents do not matter, but this is not the intention at all. Pinker says:

"Parents can certainly harm their children by abusing or neglecting them. Children appear to need some kind of nurturing figure in their early years, though it needn't be a parent ... Parents select an environment for their children and thereby select a peer group. They provide their children with skills and knowledge, such as reading and playing a musical instrument. And they certainly affect their children's behaviour at home, just as powerful people can affect behaviour within their fiefdom. But parents' behaviour does not seem to shape their children's intelligence or personality over the long term." (italics are mine).

Going back to my fictitious scenario at the beginning of this post where the mother asks, "What kind of person will you grow up to be?"; the answer is fate. Children are not lumps of clay for parents to mold - in fact, a child's attitude can also affect the way the parent treats her.
But parenting is an important, satisfying and ethical responsibility, and it goes without saying that it is not right to mistreat one's children. One of Pinker's closing comments on this topic:

"There are well-functioning adults who still shake with rage when recounting the cruelties their parents inflicted on them as children. there are others who moisten up in private moments when recalling a kindness or sacrifice made for their happiness, perhaps one that the mother or father has long forgotten. If for no other reason, parents should treat their children well to allow them to grow up with such memories."

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