The genome and "nature vs. nurture"   

Published in the MDI Islander Friday, August 22, 2008

The human genome is the blueprint for our the body, encoding genes that encode proteins that do manual labor. It’s easy to appreciate why we look like one or both of our biological parents. A tall, thin boy with brown eyes inherits genes that lead to a "tall, thin" body shape (from skinny old dad), and encode more dark pigment (from brown-eyed mom), etc.

But what about personality, moods, compulsions, susceptibility to disease? Since these more malleable attributes are carried out by body parts (e.g. the brain, the immune system), and since body parts are determined by genes, aren’t these attributes hardwired as well? Aye, there’s the rub.

This question of "nature vs. nurture" has been debated since science began to emerge in parallel to religious beliefs, questioning who we are and how we relate to the world around us. Many studies comparing identical twins reared apart, versus together, of adopted children, and even of first-degree relatives, illustrate that nurture has quite a lot to do with it.

But as we learn more about genes, we can account for many of our quirks as being associated with specific genetic variants. So, which is it, nature or nurture? Most of us instinctively sense that it’s a bit of both. But this may not be the right way to look at it. We should instead ask: How does our genome allow us to respond to the world around us?

We already have a hint, in the context of evolution. Charles Darwin would suggest that the genome responds to the environment by allowing new changes (mutations) in genes, which would be the fuel for natural selection, hence, "survival of the fittest."

Whether you agree or not, this is a long-term view. Natural selection doesn’t exactly show its cards in a lifetime, or even in a century. Many generations are required. But still, we adapt to the world around us in much shorter order. How this happens is the subject of intense study.

The general explanation is that the genome is the world’s best hedger of bets, if you will, setting us up for a great degree of buffering, or margin of error. One way to think about this is like a bowling lane with bumpers in the gutters, such that your ball can make it as far as the pins, but it is up to you whether you knock down 10, five, one or no pins.

Advanced creatures like humans are equipped for a range of environmentally, sociologically and even randomly determined possibilities. Not an infinite range, though. No animal would survive a meteor at ground zero. Not everyone can be a Rhodes scholar. Most will never hit a golf ball like Jack or Tiger or, or play music like Segovia or Charlie Parker, break a drug addiction, or recover quickly from a stroke or an infection. But in the eons it takes for a complex species to evolve, its genome encounters a number of situations through which the organism has survived. It’s the collective genomic response to these experiences that gives the ability to adapt to a range of more reasonable possibilities.

The immune system is one example of this, potentially encoding many types of antibody so that it is ready for all kinds of bacteria (whether or not it has been seen before). The brain (if you are reading this, you already know what it does) is the ultimate example of this adaptation principle. Adults have around 100 billion cells called neurons, which altogether make trillions of connections to form networks and hubs of activity. These hubs define our behaviors, our senses, our thoughts, equipping us for way more possibilities than there are stars in the galaxy. Babies have even more connections, which after birth are lost or refined as they sense the world around them, and further modified with experience. Amazingly, despite all this, the basic wiring of the brain is probably completely programmed by genes. While the ensuing changes are determined by interaction of the basic wiring with experience, available possibilities are the result of eons of genetic changes, just waiting to pounce on the next opportunity.

So, you can see why "nature vs. nurture" may not be the best way to frame the question. It’s like that the famous quote from U.S. Pres. John Fitzgerald Kennedy: "Ask not what you can do for your genome, but what your genome can do for you." And you wonder why I got a "C" in history?

Bar Harbor resident and Jackson Laboratory Professor Wayne Frankel, Ph.D., studies the mechanisms of brain diseases, including inherited epilepsy.  Dr. Frankel welcomes your feedback on his column.

More articles by Dr. Frankel

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