Evidence that human skill level is more reactive to developmental history than to genes or environment

The human brain is influenced by genes ¹ , environment ² , and developmental history ³ . Extensive efforts seek to identify the causes of observed variation in behaviour and disease ^4–6 . Moreover, it is of primary interest to predict the brain’s response to influences, both at present and over our evolutionary history ^2;7–9 . Here we use a mathematical model that mechanistically recovers major aspects of human brain development and evolution ^10–12 to predict the response of adult skill level to point influences earlier in development. We show that adult skill level is much more reactive to changes in developmental history than to genetic, environmental, or social changes over life during the recovered evolutionary trajectory from H. habilis to H. sapiens . This occurs despite our finding that adult skill level has evolved an increased reactivity to environmental and social change, and a decreased reactivity to genetic change, which is consistent with observation ^13–15 . We further show that adverse genetic and environmental conditions that would developmentally yield low adult skill level can be more than compensated by time-specific changes in the environment or by slight changes in developmental history, yielding outstanding adult skill level. Our analyses identify developmental history as having a major ability to influence adult human skill level.