If human development depends largely on the external environment then why is it that siblings, even identical twins, have different emotional responses?

One child might become an addict or have behavioural difficulties while the other does not.

The answer is that no two children have the same environment and the same parents.

The Changing Emotional State of the Parents Matters More than Their Physicality

If the parents are stressed during one pregnancy as opposed to the other or their relationship alters or the financial situation changes, there will be an impact on the child's development.

Moreover, human development has a recursive nature, which means parents are also shaped by the children and can be triggered in response to each child’s unique temperament. Parent-child relationships can be improved when parents are more conscious and mature about their responses to their children’s unique natures.

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