Explain how intelligence is the result …

Intelligence is the results of both hereditary and environment as follows:
Hereditary: The effect of hereditary on intelligence comes from the studies on twins and adopted children. The intelligence of identical twins brought up together shows a correlation of 0.90, while identical twins reared in different environments co-relate 0.72 in term of intellectual, personality and behavioural characteristic. The intelligence of fraternal twins slows a correlation of 0.60 and that of brothers and sisters correlates 0.50. Another study shows that children's intelligence is more like their biological parents than their adoptive parents.
Environment: Studies have shown that a with the growth of children, their intelligence tends to match that of their adoptive parents. Children from disadvantaged backgrounds and adopted into higher socio-economic status families shows a large increase in their intelligence levels. Rich nutrition, good family background and quality schooling increases intelligence, while environmental deprivation lowers intelligence.

Thus, it could be concluded that intelligence is an interplay of both (nature and environment). Both hereditary and environment go hand in glove in determining intelligence.