In this era of rapid genetic discoveries, this topic is discussed and debated more than ever. And yet while our genetic predisposition lays the groundwork for our existence, it is our experience in utero, at home and in our world that gives us our final form and substance.

Current genetic research through an understanding of inherited disease and basic biology and chemistry discerning how genetic information in the form of DNA provides the critical signals that instruct our cells how and when to multiply; how they are to develop into distinctive cell types to form individualized organs; how to respond to chemical signals from elsewhere in the body; how to respond to stimuli, beneficial or threatening, in our environment.

We know that an inherited defect in an enzyme may lead to a chemical imbalance in the body in phenylketonuria (PKU). This results in mental retardation unless a special diet is initiated soon after birth (all infants in the U.S. are screened for PKU at birth). We know that an inherited defect in a specific protein needed to maintain the structure of a muscle fiber leads to deterioration and scarring of muscle and causes muscular dystrophy. We know that there exists pieces of DNA or genes that help cells or tissues grow but that also prevent excessive growth. If dysfunctional because of an inherited defect, they may predispose a person to uncontrolled cell growth (and cancer) at a later age.

Despite all the above, one's health destiny is not finalized at conception or at birth. Perhaps in time, geneticists may be able to predict accurately, based on an individual's complete DNA pattern, the physical and perhaps mental characteristics and challenges that person will encounter in her/his lifetime. But how that individual develops as result of those characteristics and challenges will be far harder to predict because there are an infinite number of possible outcomes. That accounts for why identical twins separated at birth may have similar physical characteristics but different personalities. While the human form, inside and out, is now predictable to a greater degree by DNA, the essence of a person's humanity is determined by both his/her capacity to sense, feel, love, and learn, and the sensations, feelings, love and lessons he/she is offered. An automobile company can tell you exactly how a car is built, its operational specifications and the strengths (and flaws) of that model but what salesman can accurately guarantee how any one car will function?

I think of children as sacks containing all kinds of ingredients passed on from previous generations. But it is through living - isolation - that a recipe forms and makes from these ingredients a unique and unforeseeable creation. Neither biologic parents nor adoptive parents should underestimate their singularly critical roles in shaping a child's destiny.

Mark Korson, M.D., is a board-certified geneticist who directs the Inborn Errors of Metabolism Clinic at Children's Hospital in Boston, MA. He graduated from the University of Toronto Medical School and completed his pediatric training at the Hospital for Sick Children in Toronto, Canada.

Credits: Mark Korson, M.D.