This chapter takes a close look at the foundations of development: heredity and environment. With the joining of sperm and ovum at conception, chromosomes containing genetic information from each parent combine to determine characteristics that make us human and contribute to individual differences in appearance and behavior. Several different patterns of inheritance are involved, ensuring that each individual will be unique. Serious developmental problems are often caused by the inheritance of harmful recessive genes and chromosomal abnormalities. Fortunately, genetic counseling and prenatal diagnosis help people at risk for transmitting hereditary disorders assess their chances of giving birth to a healthy baby.

Environmental influences on development are equally as complex as hereditary factors and play a powerful role throughout the lifespan. The family has an especially powerful impact, operating as a complex social system in which members exert direct, indirect, and third-party influences on one another. Family functioning and individual well-being are influenced considerably by socioeconomic status differences in child-rearing practices as well as poverty and homelessness. The quality of community life in neighborhoods, schools, towns, and cities also affects children’s and adults’ development. Cultural values as well as laws and government programs shape experiences in all of these contexts.

Researchers view the relationship between genetic and environmental factors in different ways. Some believe that it is useful and possible to answer the question of how much each contributes to behavior. Others think that the effects of heredity and environment cannot be clearly separated. They want to discover how these two major determinants of development work together in a complex, dynamic interplay.