What is the relative contribution of genetics vs the environment in children from birth to age two? A study by Austerberry and colleagues addressed this question in JAMA Network Open on August 22, 2022. They combined results from 21 countries in 6 continents of 31,053 identical twins (genes all the same) and 47,991 fraternal twins (genes are different just as any two non-twin siblings).
They also compared these twins raised in the same home vs twins raised apart. The researchers looked for similarities and differences in psychological traits and developmental milestones among these infants.
By comparing identical twins to fraternal twins, they found that “complex traits are substantially but not entirely” genetic. These complex traits were mainly “psychiatric, metabolic, and cognitive traits.”
Genetics were most notable for psychomotor functions, then attention functions, complex interpersonal interactions, family relationships, and emotional functions.
Twins growing up in the same home were compared to twins raised apart. These demonstrate the importance of the environment, and its interaction with genetics.
The overall result of these studies was “evidence that most domains of functioning, disability, and health in psychological and developmental milestones were heritable in infancy.” This was reinforced by comparing twins reared together vs apart.
All categories studied showed high degrees of heritability except for sleep and language functions. These last two had a strong environmental impact so that genetics played a lesser role than other types of functioning.
The authors wrote that these results “may improve public perception on nature and nurture, for example, dispelling widely held beliefs that infants are shaped entirely by their environment or that family history entirely predetermine child health, beliefs that may place undue pressure on parents.”
