What propels an embryo from one stage to the next-and makes one species different from another-is not a blueprint but rather an enormous autonomous l… - Gary F. Marcus

The psychologist Abraham Maslow famously suggested that after we take care of our most basic needs, such as food, shelter, and sex, we eventually strive for “ self-actualization,” or the realization of our full potential; in his words, “[Even if all our other] needs are satisfied, we may still often (if not always) expect that a new discontent and restlessness will soon develop, unless the individual is doing what he [or she] is fitted for. A musician must make music, an artist must paint, a poet must write. What a [person] can be, he [or she] must be.

If there is not preformation, and no blueprint, there is also no getting away from the environment. Genes do not guarantee particular products; rather, they provide particular options: To every gene there is an IF, and with that IF comes an option. In many cases, those options are selected based on cues from the environment, and it is for that reason, more than any other, that the answer to the nature-nurture question is not one or the other, but both.

What Jacob and Monod had discovered, in essence, was that each gene acts like a single line in a computer program.