Nature, nurture, and twin research strategies
Describes two approaches, chorion control and co-twin control, to twin research that can reveal the nature and timing of environmental influences. Chorion control studies investigate possible prenatal influences by comparing those monozygotic (MZ) twins who shared a single placenta and chorion with those MZ twins who developed separate placentas and chorions. The co-twin control approach involves exploring environmental influences by investigating differences (discordances) in MZ co-twins. Recent research employing these approaches is discussed. Chorion control studies are revealing that monochorionic (MC) MZ twin pairs can be more dissimilar than dichorionic (DC) MZ twins with respect to birth weights and some medical conditions, but more similar with respect to some important psychological characteristics, including certain aspects of health, personality, and intelligence. Co-twin control studies provide opportunities to explore the environmental influences that occur over the course of a lifetime. It is evident that co-twin control methods can help clarify the timing and nature of nongenetic influences, and perhaps lead to effective interventions and prevention in cases of mental disorder.
Phelps, Jeanne A., James O. Davis, and Kevin M. Schartz. "Nature, nurture, and twin research strategies." Current Directions in Psychological Science 6, no. 5 (1997): 117-121.
Current Directions in Psychological Science