The other day I was doing some research on the origins of antisocial behavior and how one might cope with it, when I ran across a very interesting experiment. Neuroscientist Michael Meaney and his colleagues at McGill University in Montreal discovered that the way that baby rats are nurtured can be predictive of whether such individuals will grow up to be antisocial, anxious, or even violent.
They discovered that rat mothers naturally fall into two groups. One group spends a lot of time licking, grooming, and nursing their pups—about twice as much time as the other group, which seems to ignore their pups. Highly-nurtured rat pups tend to grow up to be calm adults, while rat pups who receive little nurturing tend to grow up to be anxious.
It turns out that the difference between a calm and an anxious rat is epigenetic. That is, the nurturing behavior of a mother rat during the first week of life literally turns on or off some genes of her her pups. The epigenetic pattern that mom establishes tends to survive, even after the pups become adults.
We’re used to thinking of inheritance in terms of the letters of the DNA code that pass to us from our parents—through eggs and sperm. But the rat-licking story tells us that there is another path to the offspring’s DNA. Through her licking behavior, a mother rat can write information onto her pups’ DNA in a way that completely bypasses eggs and sperm. In a sense, her nurturing behavior tells her pups something about the world they will grow up in. Mom’s behavior actually programs the pups’ DNA in a way that will make them more likely to succeed or fail.
This line of research goes back at least to 1957, when psychiatrist Seymour Levine showed that baby rats that had been taken away from their mother for 15 minutes each day grew up to be less nervous and make lower amounts of a stress hormone. He guessed that it was not the human handling, but the extra licking and grooming the pups received when returned to their anxious mothers, that destined the pups for greater tranquility.
The reason, the researchers discovered, was that these rats had developed more brain receptors for glucocorticoid, which provides a feedback mechanism that helps shut down excess hormone production. The study shows a strong biological basis and experimental proof of these effects. Human stress chemistry is similar to that of rats, and overproduction of glucocorticoid hormones can increase the risk of heart disease, diabetes, alcoholism, and other diseases. But no human studies have yet examined the impact of subtle differences in early childcare on stress hormones and susceptibility to disease.
It seems to me this research is relevant (given my recent experience with antisocial behavior) and provides an answer to the question whether pro-social behavior “has to be in you” to be manifested.
While this all might sound a bit dreary—that your outlook on life and your own parenting is determined by how you are raised (something you don’t have control over)—one bit of additional research is more hopeful: if the high-stress rats were put in a low-stress environment as adults, epigenetic markers were still changed, resulting in a low-stress animal.
So things may not be set in stone as much as they may they seem at first blush.
The subject of inheritance is germane to any discussion of throw-away kids and their changeability. To explore the subject further, you may be interested in listening to this Radiolab program.
Groove of the Day