Your understanding isn't correct, at least for nursing.

Nurses were male until the 1800s. https://en.wikipedia.org/wiki/Men_in_nursing#History give examples of predominately nurses and caregivers in other cultures before that time. http://minoritynurse.com/rethinking-gender-stereotypes-in-nu... says "Before modern day nursing, men were nurses, not women. The earliest recorded nursing school was established in India around 250 B.C. It was exclusively for men; women were not allowed to attend because it was believed that women were not as pure as men."

What happened in the 1800s? Quoting from https://files.eric.ed.gov/fulltext/EJ1081399.pdf :

> Through the efforts of Florence Nightingale in the mid-nineteenth century, nursing was established as a women's profession (Hus, Chen & Lou, 2010). Nightingale's image of the nurse as subordinate, nurturing, domestic, humble, and self-sacrificing, as well as not too educated, became prevalent in society. The American Nursing Association ostracized men from nursing until 1930, when as a "result of a bylaw amendment, provision was made for male nurses to become members of the American Nurses' Association" (In Review - American Nurses' Association, p. 6). Looking back in nursing history, Florence Nightingale, and the American Nursing Association ostracized men from the nursing profession.'

See also http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2648.1997.... , "History appears to indicate that men have had a place in nursing for as long as records are available, but their contribution has been perceived as negligible, largely because of the dominant influence that the 19th century female nursing movement has had on the occupation's historical ideology."

If there is an imbalance in intrinsic inchoate biases, such as if men tended to unconsciously hire 55% men and 45% women, whereas women preferred to hire 50% each, then an initial 50-50 split, but with no other biases in play after someone enters the field, would drift towards an equilibrium at around .5263 men and .4737 women. More men magnify the male bias towards males.

My other assumption was that early movers have a magnified effect on the future of the field. Think about how any arbitrary decisions made by Turing or von Neumann could still be affecting computing today, like the sign convention for the charge on an electron--that could have been +1 instead of -1, and many of the signs in physics equations would be flipped. If a female had been making those decisions, we might be using a different computing paradigm that would better match female thought patterns. Computing as we now know it initially came about through the confluence of war and academia. Mathematicians designed machines to aim artillery pieces and automate military-grade ciphers, and then to automatically break automated ciphers. The development of computing has occurred rapidly and recently, and after air travel and telephony, such that there really is only one global culture for it. The body of work is already so large, and readily available to everyone, that starting from a different foundation today really does require the fictional time stasis bubble that I described.

You would have to look back into history, when culture barriers were stronger, to look for examples of computing devices that may have been used preferentially by men or women.