It's perhaps the most controversial question in biology: Are we shaped by our genes or by our environment? The debate extends even to the womb, where the chemistry of the fetal environment may play as much of a role in our development as the genes we inherit from our parents.
Now, scientists believe they have found a clever way to disentangle the effects of genes and environment in the womb. The solution is to look at babies conceived in a lab by in vitro fertilization (IVF) and carried during pregnancy by women who are genetically unrelated to them.
The team, led by Frances Rice, a psychologist now at University College London, focused on two traits usually associated with smoking during pregnancy: low birth weight and antisocial behavior. Experts believe that carbon monoxide from cigarette smoke can lead to low birth weight, but they are divided over whether genes or prenatal environment contribute to temper tantrums and disobedience. The researchers looked at the medical records of nearly 800 children born in the United Kingdom between 1994 and 2002 and conceived with IVF. About a quarter of them were not genetically related to their mothers, and 6% of all the mothers smoked during pregnancy.
Regardless of whether the mother was related to her child, smokers' babies were 11.4% lighter at birth than the children of nonsmoking moms, the team reports online this week in the Proceedings of the National Academy of Sciences. The findings agree with studies showing that birth weight is dependent on the chemical environment in the womb, Rice says.
To test the contribution of nature and nurture to antisocial behavior, the team asked the parents to fill out a questionnaire about their children's moods and personality traits. The average child scored a 1.86 (out of 10, where 10 is the most misbehaved), which is similar to the national average. But those born to smoking mothers scored an average of 2.40. When the researchers compared children born to genetically related vs. genetically unrelated smoking moms, they found that related children scored an average of 2.54 on the antisocial questionnaire versus 1.77 for unrelated children. That means that tantrums, fighting, and lying are more likely the result of genes than a smoky womb environment, according to the study.
The authors "are to be commended for the use of a novel design" to tell the difference between the effects of pregnancy environment and genetics on offspring health and development, says Lauren Wakschlag, a psychologist at the University of Illinois in Chicago. But she cautions that the sample of smoking mothers is probably too small to make solid interpretations from the results.