No one knows for sure how life began.
Scientifically speaking it has been reasoned that very primitive forms of life like amoeba originated and gradually became organized, became more complex evolving into life forms that evolved in stages like a fish, an animal and man in several avatars with increased function of mind action over the body. Darwin has a popular theory of evolution based on competition,survival and adaptation.
Males and females of every species know well how they can initiate life but know almost nothing beyond that.. The male earns or hunts food and provides protection against the elements, the female cares until the young acquire their own capacity to care for themselves.In no other way they know how by artificial means can new life be created or controlled.
Spiritually it is believed in many faiths that life is given in and taken out by a Superior composite form that is structured both ways, integrated in all living entities and at the same time contained within every life form.This spiritual awareness varies across all life forms in many cultures.
Worship of Shiv-Ling including yoni form is a Bhakthi addressal to the Superior form contained in us about the mysterious cyclic process of creation,sustenance and eventual amalgamation with myriad individual and social group connections.
It is not worship of the likeness of our own body parts meant for duplication.It is the nature of connection to the Supernatural regarding Adwaithic identity designed to removes ego-centrality. Main difficulty is due to extreme variance in modes of dependence to God manifested in such vagueness and awareness amongst us.