Chimerism is what happens when cells from one twin are present in the other. For example, white blood cells with Y chromosomes would be found in the female twin. Vigier et. al, 1989.
Piaget's theory of cognitive development. Piaget's theory of cognitive development is a comprehensive theory about the nature and development of human intelligence. It was first created by the Swiss developmental psychologist Jean Piaget (1896â1980).
Lesson Summary. Jean Piaget developed a theory of cognitive development which involved four distinct stages. Each stage is signified by a distinct milestone to be achieved. The first stage is the sensorimotor stage and the milestone for this stage is object permanence.