We are the products of our mother's and father's genes (more Mom than Dad), but a modern understanding of genetics and biology shows us that how our genes are expressed are the product of our environment and what we do. How can that be, when we are allotted a certain genetic hand of cards at conception?
The science of epigenetics explains a lot (and leaves us with a lot of questions too). It turns out that genes can be silenced or turned on depending on how we live, and how we are treated. The body is not just a complicated jelly bag of enzymes and muscle and protein regulation; the very genetic material that directs all the regulation can change shape and redirect what goes on in the first place. So our genes regulate our proteins, but our proteins also regulate our genes.
Following the study of epigenetics, we also end up with the idea that what we do (and breathe and eat) affects our children and grandchildren, too. For example, in a small European community during World War II, babies were born smaller than usual. It makes sense. There was less to eat. But the children who were born smaller then grew up and had smaller babies themselves. Even more bizarre, epigenetic studies show that if your paternal grandfather had plenty to eat between the age of 9-12, your average lifespan is likely to be shorter than someone whose paternal grandfather didn't have enough to eat during that same critical age (1).
Why is this whole concept important to psychiatry? It's all about the brain. The brain has 100 billion neurons. 1.25 terrabyte memory capacity. 100,000 kilometers of connecting neuronal cables (2). Our human brains require many years of careful nuturing and protection as they reach maturity. The wiring process as we grow up depends upon a multitude of factors - nutrition, appropriate social attachment, education. Even after we are fully mature, the brain is still capable of change, or else we could never learn anything new.
Humans are all very closely related. There appears to have been a genetic bottleneck about 2000 generations ago, so that all of us are descended from a small family group that lived 50,000 years ago (3). Two randomly chosen humans have closer genetic similarities than two chimpanzees chosen from the same social group (2). There have been a number of changes over the last 2000 generations, but we are still so much more the same than different. The contention that "all men are created equal" has more scientific truth to it than one might think.
Let's pull all these separate threads together - we are born with a certain genetic hand. We can alter that hand for ourselves, our children and grandchildren by how we live. The brain is the most complicated organ in existence, and the interplay between our genes and how we live will affect the brain in countless ways. Finally, we are all brothers and sisters, and, with few exceptions, have enormous genetic potential for success.
Hardly any of us are doomed by our genes to be obese, diabetic, or depressed. There are simply too many other factors at play to make that flat statement. Yes, if your parents are obese, and you eat and do the same things your parents do, you are more likely to be obese yourself. The logic follows that if we eat and do similar things to what our lean ancestors did, we will be lean. We can't just wait for a new diet pill, a new surgery, a new exercise contraption to solve our problems for us. There are too many factors at play.
With the brain, the factors expand a thousand fold. Lifestyle, nutrition, and proper nurturing are more important for the brain than for any other organ. Hopefully, now, we can finally use medical science to address the whole picture, instead of looking for a single magical chemical or pill. We're all meant to be strong, smart homo sapiens - and we can be, if we work at it. And if genes are our destiny, then we are meant to be that small, intrepid band of humans who conquered the world, for good or ill.