According to Francis Galton, heredity does not go to immediate parents but to remote ancestors. Only fifty percent of the heredity is due to

By Galton's law of ancestral heredity, the two parents together contribute about fifty percent of a person's heredity.

He held that inheritance traces back through remote ancestors, each generation adding a diminishing share.

In his scheme the two parents supply one half, the four grandparents one quarter, and so on in a halving series.

Great grandparents therefore contribute a still smaller fraction, well below the fifty percent from parents.

Grandparents contribute about one quarter, not the half that the question asks about.

Francis Galton, cousin of Charles Darwin, founded eugenics and pioneered the statistical study of heredity.