What Makes Girls Play House and Boys Play War?

The reasons why girls and boys gravitate toward dolls or trucks may have more to do with genetics for girls and environment for boys, according to a new study.

Researchers compared the impact of genetic and environmental factors on gender role behaviors in preschool boys and girls and found that genetics appear to play a larger role in shaping girls' gender-specific behaviors while environment may be a bigger factor for boys.

Although a child's genes explain many of the differences in whether they adopt feminine or masculine behaviors, researchers say little is known about the extent to which genetic vs. social and environmental factors contribute to individual differences in gender role behaviors, especially during the preschool years.

For example, researchers say some boys are extremely masculine in their choice of toys, games, and other activities at a young age, while others are less so. But the reasons behind these individual differences are unclear.

Read WebMD's "Tomboys May Be Born, Not Made"

Genes vs. Environment in Shaping Gender Roles

In the study, which appears in the July/August issue of Child Development, researchers analyzed the effects of genetic and environmental factors on the gender-role behaviors of a group of nearly 4,000 3- to 4-year-old twins and nontwin sibling pairs.

Researchers say they compared twins vs. nontwin siblings because twins share identical genes while sibling pairs only share about half their genes.

Their results show that the extent to which genetic and environmental factors influence gender role behaviors differs for boys and girls.

For example, the study showed that genetics seemed to have less of an impact on whether or not boys adopted masculine-type behaviors, such as playing war games. While environmental factors, such as the boy's role models or peers, had a bigger affect on their adopting typically male behaviors.

In contrast, genetics had a substantial impact on girls' gender role behavior, while the environment played a less significant role in girls' selection of typically feminine behaviors, such as playing with dolls.

Finally, researchers say their findings indicate that the influences of shared environmental factors on gender role behavior may be more important in early childhood than in adolescence and adulthood.

Read WebMD's "Girls Lose Interest in Activities As they Age"

By Jennifer Warner, reviewed by Brunilda Nazario, MD

SOURCES: Lervolino, A. Child Development, July/August 2005; vol 76. News release, Society for Research in Child Development.