The earth gives life just like woman gives life. This seems to have been the belief of many different cultures from ancient times until now, particularly in cultures where life's greatest mystery was even more inexplicable than it is to us today. Paleolithic sculptures of a woman with extremely emphasised breasts, abdomen, genitals, thighs and buttocks have been found in a broad belt from Southern Europe to Northern Russia. They depict the divinity most important to these people, the one who ensured that food grew from the earth. To us, she survives as Mother Nature, or the Goddess to some.
In the eighteenth century, our good friends the civilised people became interested in the mother goddess - first from discovering that there existed matriarchal societies around the world where such a deity was still worshipped, later from discovering the female figures of such a goddess from their own stone-age past. Venus of Willendorf is symbolical for these finds, which created a whole new theory about an interesting past before the patriarchy.
The mother goddess had a prominent place in the first civilisations of the Middle East. The Sumerians worshipped Inanna, the Egyptians Isis, among Babylonians and Assyrians she was Ishtar. The Phrygians and Lydians called her Cybele and in Syria and Palestine she was known as Astarte.
In all ancient European mythologies at least one mother goddess, often more, can be found. The Greeks worshipped her in the aspects of Gaia (Mother Earth), Demeter (goddess of growth and fertility), Aphrodite (goddess of love), Hera (the chief god's consort), and Rhea (the ur mother). Along the same vein, she was Tellus, Ceres or Ops, Venus, and Maia to the Romans. The Celts often worshipped three bare-breasted ladies called the Modron, while the Vikings went for Freya and possibly others.
In Hinduism, where the pantheon has been allowed to grow through the millennia, the great goddess in several manifestations is still worshipped. She is known as Devi, the mother who gives life, and Kali or Durga, the destroyer who takes it. Other important goddesses which can be said to be aspects of the one are Parvati (Shiva's consort], Aditi, the mother of the sun and moon, Bharat Mata (Mother India), or Bala, Bhavani, Devaki or Ida among many others.
And although the Virgin Mary is not exactly a fertility symbol - quite removed from sexuality as she is - she is seen by many as the greatest Mother of them all.