Could something seemingly so individualistic as someone's personality be influenced by parasites? What about the broad differences in social norms seen between cultures? University of New Mexico Biologist Randy Thornhill recently documented the connections between microscopic pests and the character of those they infect.

Thornhill and his colleagues believe that parasitic diseases have been major factors shaping human psychology and behavior. They hold that people have a behavioral immune system, supplementing the physiological immune system, which helps people avoid and manage infections.

Characteristics such as obedience to authority are most closely related to parasites that are transmitted from person to person, rather than parasites that are mainly transmitted by other animals. The authors argue that democracy, women's rights, individual freedom, and political liberalism are facilitated by lower risks of human-transmitted parasitism. The results of their study support these predictions.

Also, women are less willing to engage in short-term sexual relations when human-transmitted parasites are more prevalent. People were more extraverted and open to new experiences when these parasites are less of a threat. Societies with high human borne parasite risk are less individualistic and more collectivistic as well as more family oriented.

The framework provides a guide to understanding why populations inhabiting different parts of the planet can be very different, as well as quite similar.

The study appears in the current issue of Evolutionary Psychology and is accessible at: What Do Parasites Have to Do with Personality and Politics?.

For more information contact, Randy Thornhill, or telephone, (505) 277-9516.

Media Contact: Steve Carr, (505) 277-1821; e-mail: