Developmental trajectories in cognitive-behavioral phenotypes: Introduction

Developmental trajectories in behavioral phenotypes are important areas for systematic research and have been for more than 30 years. They interweave several important strands related to human growth: that of individuals born with some form of intellectual impairment or disability (ID); second, the genetics associated with intellectual ability and disability; and third, at the behavioral level, the dynamic expression and variability of specific abnormalities as individuals age. ID, and the genetic disorders that produce ID, were often not well-received by earlier societies. While the inheritance of behavior and intellectual ability has probably been observed throughout human history, the systematic investigation of the inheritance of intellectual ability probably begins with Sir Francis Galton, in his treatise Hereditary Genius in 1869. The dynamic features of ID have its roots in late 19th century developmental psychology and early 20th century pediatrics. Alfred Binet, along with his colleague Theodore Simon, created the first methods of formal intelligence testing of children for the French school system. Scores based on the items administered would then be used to distinguish children who were prepared for enrollment in a standard educational program from those who were not. The confluence of these research topics brings us to the subject of our Special Issue.