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Richard and Steven were brothers, with Richard six years older. The quality of maternal care was essentially the same for the two boys, as were their general environmental conditions. Both boys had IQ's measured in the superior range. Richard was an extremely easy baby to care for. He ate and slept well, cried very little, and was happy, quiet, and contented. He never ventured far from where he was placed and at the age of eight months would play happily in his playpen for long periods of time with the toys left within his reach.
Steven, on the other hand, was far more active as an infant and he reacted more vigorously to stimuli, startling easily. He often had to be rocked and sung to sleep. When he was a few months old, his mother would place him on a small rug in her room. Time and again he would, with great effort, pull himself along on his stomach until he reached the place where the edge of the rug met the hardwood floor. There he would stop and with great interest and concentration scratch the rug and then the floor, obviously intent upon experiencing the difference in texture between the two surfaces. That his interest and curiosity were inherent there can be no doubt, as was the innate physical vigor that he used to gratify his curiosity.
When Steven was eight months old, he rebelled against being confined in a playpen. His mother devised a series of gates and doors that allowed him the run of several rooms. The family, going in and out of this area, would use a particular door that closed with a slight click. When this door did not fully close as evidenced by its failure to click, Steven would come scrambling on his hands and knees from the opposite end of the area and