Preformationism

Preformationism is a historical biological theory that existed before the discovery of modern genetics. It posited that organisms develop from pre-existing miniature versions of themselves, known as "homunculi." According to this view, all the traits of an organism were thought to be fully formed at the time of fertilization or were contained in the sperm or egg, and development was merely a process of growth and unfolding, rather than a process of complex development and differentiation from simpler forms.