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).
In other words, cognitive development is the emergence of the ability to think and understand. A large portion of research has gone into understanding how a child imagines the world.Jean Piaget was a major force in the establishment of this field, forming his  theory of cognitive development .Piaget proposed four stages of cognitive development: the sensorimotor, preoperational, concrete operational and formal operational period. Many of his theoretical claims have since fallen out of favor. large portion of research has gone into understanding how a child imagines the world. Jean Piaget was a major force in the establishment of this field, forming his  theory of cognitive development .