Answer:
It was a simplistic grescale scenario devoid of unnecessary features. Think a simple and fast 3D render from the 90s or something. So everything was grescale, the person had no gender (or even features), and pushed a baseball sized sphere on a simple rectangular table made of indeterminate materials. Now I can picture something more detailed if required or desired but my mind focused on the mechanics of it all and kept details to a minimum. Asking for these details afterwards doesn’t generate them retroactively.
A population in which births are overwhelmingly female means those who give birth to males have an advantage in passing down their genetic material. In your scenario a man will likely have more descendants than a woman, so genes that arise promoting male children would be favored. If you reverse the ratio and the population is overwhelmingly male then being female gives you an advantage and genes promoting female children would become favored. So you get a tug of war that balances out at roughly 50/50. This is known as Fischer’s principle.