When my kids were born, about 30 years ago, i knew they had inherited about half their DNA from me. At the time, the transfer of DNA from sperm or egg to an embryo was thought to be the only way that heritable information could flow from parents to children, at least in humans and other mammals.
Of course, I understood that DNA is not destiny. Yes, many characteristics of a child may be written into his or her DNA and specifically into protein-coding genes—the sequences of DNA code that dictate the shapes and functions of proteins, the workhorses of the cell. But nurture matters, too. Many of the contingencies of life—what we eat, what pollutants are in our environment, how often we are stressed—affect how the genes operate. Social and environmental influences are often invoked, for instance, to explain why identical twins can end up with different diseases despite having highly similar complements of genes.