FIGURE A Morbidity rates by socioeconomic status level.

stability or homeostasis through active change, to refer to this process of adaptation,” Dr. McEwen said. If allostatic mechanisms remain on too long or are overused, they increase the “allostatic load,” a measure of the physiologic cost to different systems in the body from repeated burdens in one’s life.

Other contributions of biology to psychosocial studies include providing information on the biological basis of resilience, often referred to as “positive health”; on the early warning signs for the risk of disease, called “predisease pathways”; and of course on the human genetic code, and the expression of its genes, now in the process of being deciphered.

Biologists can provide information on the interactions between the body’s systems, Dr. McEwen noted. For example, diabetes, renal disease, and depression were the subjects of a workshop earlier this year at the National Institutes of Health. Other problems that need study across systems, he said, include cognitive disability in chronic pain and chronic fatigue; the consequences of sleep deprivation (which involve changes in immune func-