WALTER WITSCHEY
SCIENCE
The question is nature versus nurture. Are we more a product of our DNA or more the result of our environment and upbringing? A new and surprising answer -- both -- is emerging in the field of epigenetic research. (Epigenetic refers to switching information carried on the genes, not in the basic DNA code itself.)
A fresh view, emerging in the past few years, says we inherit more than DNA from our parents.
An early breakthrough was the realization that some DNA was in the mitochondria, which are energy-producing structures outside the nucleus of the cell -- in particular, m-DNA in egg cells passed from mother to child.
Comparing mitochondrial DNA from many individuals worldwide led to the conclusion that all modern humans are descended from a single female "Eve" living in eastern Africa about a quarter-million years ago.
The story, however, gets more interesting.
Switching is crucial
DNA operates in a complex switchboard environment. Genes (the long strands of DNA that code for protein-making) may be switched "on" or "off."
The switching is crucial to our development and good health.
Lung cells carry the genes for making skin cells -- but in the lung, they are switched off. Likewise, skin cells carry the genes for making kidney cells, but thankfully, they are switched off. Only the genes for making new skin cells are switched on in the skin.
Switching genes on and off is the job of small 4-atom molecules, methyl groups (one carbon atom and three hydrogens), that attach to the outside of the DNA strand. When attached, the gene is suppressed. If missing, the gene is expressed (and contributes to cell chemistry and protein-building).
Because genes are helpful on one occasion, and harmful another, switching is critical.
Until recently, researchers believed that DNA was "stripped bare" of its markers and switches in each new birth. Work by Randy Jirtle of Duke University demonstrates that switch settings can be passed along to offspring.
Gender's effect
Subtle environmental changes can add to or remove methyl groups (the switches) from DNA. Diet, vitamins, smoke, poisons, toxins and stress all play a role. As a result, a woman transmits environmental as well as DNA information to her fetus at conception.
Gender has a huge lifelong effect on the genetic switches, through the action of hormones and other mechanisms.
The genetic switchboard responds to gender in hundreds of ways to produce noticeable differences in brain and body function in men and women.
After birth, parental care and love for an infant releases serotonin in the brain, which alters genomic switches, reducing stress and shaping behavior for life.
Implications for social policy abound in this.
Whole classes of individuals (criminals and the poor, for example) have been dismissed by our society as "having bad genes" and "doomed for life."
Epigenetics carries a hope that there are changes possible, such as with diet, green tea, and vitamins, as well as in designed-to-purpose drugs that may reset some of the inherited epigenetic switches and cause dramatic, positive, lifelong change.
Dr. Walter Witschey is director of the Science Museum of Virginia. Contact him at WWitschey@SMV.org and look for his column on the fourth Thursday of each month.
