The scientific picture of how genes work is much more complex than people tend to think, though you’d never guess this from the newspapers. Frequently there will be an announcement suggesting a direct connection between genes and traits or conditions (‘Gene for autism finally discovered!’). One gene is said to give you brown eyes; another, blonde hair; and yet another, schizophrenia. The notion of the “selfish gene” conveys the idea that one gene works in isolation, going about its own selfish business.
It does not make sense to consider a gene in isolation as being responsible for a complex function. Genes are not so powerful. For each biological function, there is always a series of genes working together. Cooperation of genes with each other is the main operational basis of genetics, and therefore of evolution. Dawkins acknowledges a role for gene-gene interactions in The Selfish Gene, noting that ‘the effect of any one gene depends on interaction with many others.’
When saying that a gene causes X to happen, what is meant is that on the average X happens, and at a statistically reliable rate. There is always lots of variability, including individuals in whom nothing happens or even the opposite of X occurs. When thinking about genes, it is important to remember words like on “average,” “typically,” “usually,” “often,” “tend to,” and “generally”. Genes are very far from being fixed in their actions. And a large part of evolution occurs by altering regulation of genes, rather than genes themselves.
The vast majority of genes extract certain kinds of information from the upbringing and environment of the person. Genes are very good at simple if-then logic: if in a certain environment, then develop in a certain way. Complex behaviors like nurturing, especially when tied to even more complex emotions like "love," are never either genetically predetermined or environmentally produced. Gene/environment interactions are everywhere.
Right from birth, it’s very hard to distinguish the contribution made by nature from that of nurture. A "bad" genotype does not condemn a person to a particular behavior; for ill effects to occur, a bad environment is also required. Likewise, a "bad" environment is not a sentence; it also requires a "bad" genotype if it is to produce ill effects . The environment, as well as the genome, has an enormous influence on the personality of a child, mainly through the child's peer group. A hormone can make you nicer or nastier depending on your values. A criminal personality, even if partly genetic, is much more likely to be expressed in a criminal environment.
Even brain structures can be modified by external factors. Childhood adversity can scar everything from our DNA to our cultures, and effects can be lifelong. We haven’t evolved to be “selfish” or “altruistic” or anything else. The way a person develops can be steered and adjusted by changes in that environment along the way. It all depends on the context. Adolescence shows us that the most interesting part of the brain evolved to be shaped minimally by genes and maximally by experience.
Even something as seemingly hardwired as our physiology — cells dividing, moving, deciding their fates, and organizing into tissues and organs — is not engineered by genes alone. Biophysical events (like chemical reactions in the cells, mechanical pressures inside and on the cells, and gravity) can switch genes on and off, determining cell fate. Take taste. When mothers breastfeed their babies, tastes of the foods they have eaten are reflected in their breast milk, and their babies develop a preference for these foods. Babies “inherit” food preferences from the behavior of their mothers.
Changes wrought by one's diet, behavior, or surroundings can work their way into the germ line and persist far into the future. Thus, what you eat or smoke today could affect the health and behavior of your great-grandchildren. Increasingly, researchers are finding that an extra bit of a vitamin, a brief exposure to a toxin, even an added dose of mothering can alter the software of our genes in ways that affect an individual's body and brain for life. DNA Is Not destiny.
Nature versus nurture is a false dichotomy. It is rather nature via nurture. Genes are not puppet masters that determine one’s behavior exactly - environmental influences are sometimes less reversible than genetic ones. Any geneticist who says that he has found an influence for genes and therefore there is no role for the environment is talking bunk. And any nurtures who says that he has found an environmental factor and therefore there is no role for genes is equally talking bunk.
A more nuanced argument about human evolution is given in The Secret of Our Success by Joseph Henrich. The central argument in this book is that cultural evolution became the primary driver of our species’ genetic evolution. What has enabled us to dominate the globe, more than any other species, while remaining virtually helpless as lone individuals? The secret of our success lies not in our innate intelligence, but in our collective brains ― on the ability of human groups to socially interconnect and learn from one another over generations.
Once cultural information began to accumulate and produce cultural adaptations, the main selection pressure on genes revolved around improving our abilities to learn various skills and practices that became increasingly available in the minds of the others in one’s group. This culture-gene coevolutionary interaction creates an autocatalytic process such that no matter how big our brains get, there will always be much more cultural information in the world than any one of us can learn in a lifetime.