The sheela-na-gig, once seen, are hard to forget.
These carvings can be found on medieval churches and buildings across Northern Europe, but more frequently in the British Isles and in the greatest numbers in Ireland.
A popular hypothesis is that sheela na gigs represent a pagan goddess, but academics believe the situation was more complex, with multiple interpretations and roles for the female character as spiritual traditions changed over time. The goddess in question usually is identified as Celtic, the hag-like Cailleach figure of Irish and Scottish mythology. Margaret Murray proposed this, as did Anne Ross, who wrote in her essay, “The Divine Hag of the Pagan Celts”, “I would like to suggest that in their earliest iconographic form they do in fact portray the territorial or war-goddess in her hag-like aspect … Mircea Eliade‘s The Encyclopedia of Religion (1993) draws parallels between the sheela na gig and the ancient Irish myth of the goddess who granted kingship. She would appear as a lustful hag, and most men would refuse her advances, except for one man who accepted. When he slept with her, she was transformed into a beautiful maiden who would confer royalty onto him and bless his reign. There are additional variants of this common Northern European motif (see “Loathly lady“).
Additional speculations are that the figures are fertility symbols, or meant to drive away evil spirits, or for luck, or to remind early Christian church-goers about the evils of lust. The thing is, these theories are probably all correct, to varying degrees, depending on the time and place and the cultural narrative woven around the sheela-na-gig by the community in context.
In the pre-Christian era, she was most likely to be a goddess figure, with all the fertility most goddess figures entail. She is the embodiment of the tautology, “Where does all life come from? It comes from RIGHT HERE.” Many goddesses in Northern Europe and Celtic lands had a “triple aspect”, where they could manifest as fertile maidens and mothers, and also as in the form of a powerful crone/hag. The sheela-na-gig could have easily been a simplified representation of the essence of this death-and-life-giving female trinity goddess.
The sheela-na-gig became a less auspicous symbol as Christianity spread in part because women were seen as monsters in the Greco-Roman civilisations where the new religion had been codified.
Women, according to Classical thought, were just all kinds of wrong. Women were emotional, animalistic, unreasonable, and a slave to their biology — the opposite of men. Ancient physicians and philosophers thought that there was something unquestionably weird about the not-male body itself. Galen, a Greek physician who was considered the utmost authority on biomedicine, considered the uterus to be an inverted scrotum which had not descended in the female due to the lack of proper male ‘heat’. This meant that women were, from birth, ‘men gone wrong’.
Like Galen, Aristotle also imagined that women were “mutilated males”. This understanding of women as mutilated/deformed men meant that women were conceptualised on some level as “monsters”, their feminine bodies a horrible admixture of human and animal. This monster/woman image has the deeper implication in that women’s bodies are anomalies which must be feared and restrained. Nevertheless, most men coveted access to female bodies and all men needed women in order to beget heirs. Women were thus a distressingly necessary evil … This simultaneous attraction and repulsion felt toward the female body has been postulated to be the key to misogynists’ secret dread and fear of women right up to the present day.
Christianity was heavily influenced by these philosophies, and the time of St. Augustine, Christian theology had taken its cues from Aristotle & Co and viewed women as inherently sinful and likely to lead otherwise innocent men into similar sins with their Eve-begotten womanly wiles. The spread of Christianity in Northern Europe would have not only pushed out the former goddess worship, it would have restructured the ideology of goddess figures. As the repositories of temptation, the female body and the vagina were fearsome, rather than awe-inspiring.
In the newly-converted Celtic lands the sheela-na-gig were likewise either reconceptualized represent something frightening (worthy of scaring away demons) or something evil (worthy to serve as a warning of sinfulness). In most places the sheela-na-gig were destroyed altogether as too uncomfortable a reminder of the terrible power of the feminine, but the Irish Celts were a such a strong matriarchal or egalitarian society initially that destroying the goddess was thought too unlucky, and thus the carvings survived … albeit now monstrous images rather than sacred representations.
The feminine aspect of divinity, however, has never really gone away, and the vaginal symbol of the sheela-na-gig still exists in hidden and unlikely places. For example, look at this picture of Our Lady of Guadalupe:
Not only is she the Queen of Heaven, she is both maiden and mother at once. Moreover, she is a sacred depiction of the vulva, a modern-day sheela-na-gig The outer nimbus is the labia majora, the folds of her cloak are the labia minora, her head is in the position and shape of the hooded clitoris, her folded hands are where the urinary meatus is located, and the crescent she stands on is the beginning of the perineum. Her symbolism is not why she is venerated; rather her veneration probably led to this depiction of her.
The feminine aspect of divinity is a tenacious part of the human experience.
As no Sheelas have been found prior to the Norman Christian period I am puzzled that you talk about them being goddesses in the pre -Christian period. We have no evidence that they existed at all.