Final answer:
Before the research of H.M. Skeels and H.B. Dye, it was believed that children in orphanages had lower IQ scores due to genetics and biological determinism, linked with ethnicity or socio-economic status. Their work showed the importance of environmental factors in cognitive development, challenging previous assumptions and highlighting the role of nurture.
Step-by-step explanation:
Prior to the research of H.M. Skeels and H.B. Dye in the 1930s, the underlying belief regarding why children reared in orphanages tended to have lower IQ scores was related to assumptions about genetics and biological determinism. These assumptions suggested that lower intelligence was innate in the children themselves, often attributed to their ethnicity or socio-economic backgrounds. This perspective overlooked the impacts of environmental factors such as stimulation, social interaction, and quality nurturing.
However, research started to demonstrate the crucial role of environment on intellectual development, showing that nurture had a significant effect on intelligence. For instance, Skeels and Dye's work revealed that cognitive development in orphanage children could improve when they received increased social and intellectual stimulation, challenging previous beliefs. Such environmental influences on cognitive abilities have been further supported by studies into the impacts of poverty, socialization, and educational access, all contributing to a more nuanced understanding of intellectual development that recognizes the substantial role of nurture over nature.