[thaumasiotes]

> Genetic predisposition to something != inevitability.

That depends on the thing. Whether you grow five or six fingers on your hands is determined by your genes without much reference to anything else. Whether you reach a "natural" height or develop stunted by malnutrition is also determined by your genes. It is more responsive to environmental conditions than the number of fingers on your hand is - but that responsiveness is determined by your genes.