There is practical importance as well as intrinsic fascination in the idea that every human being has in him something unalterable. This something is determined at the moment when a particular spermatozoon fertilizes the ovum. Although the course of development of the embryo is influenced by the vicissitudes of intrauterine life, this course is largely determined by the inherited pattern.
After birth the program of development is further modified by nutrition, trauma, and an infinitude of other environmental influences. So a person's performance is largely determined by experience and opportunity, and his appearance is largely determined by his history. Nevertheless, it has been assumed1 that the inherited something, the genotype, determines the course which the person's development will take in any given environment.
The resultant of all these influences is a person marked by many individual differences and deviations. Their extent has been revealed in recent studies by Williams.
PHYSICAL TYPES. JAMA. 1957;164(7):770–771. doi:10.1001/jama.1957.02980070052013
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