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).
A major controversy in cognitive development has been  nature and nurture , that is, the question if cognitive development is mainly determined by an individual's innate qualities (nature), or by their personal experiences (nurture).n 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.