Fertile women cycle until they are around fifty years old, at which point a phenomenon called menopause occurs, when a woman ceases to produce eggs for fertilisation. Millions of ova develop within the female unborn baby, far more than the 450 or so that are ever used, so why has this cut-off point evolved?
Cooking is now seen as the definitive characteristic of modern humans, from which all others followed. It seems to have directly led to the development of tools, especially blade design, but it had many other consequences.
Cooking, particularly of meats and fats but also starches, partially pre-digests the food, making more energy available to us and allowing us to use less to digest it. We put this extra energy into growing brains. Growing big brains burns many calories and just running them consumes a significant part of our daily food intake. We know that the physical structures which allow us to speak were evolving at the same time as our brains were growing larger. Speech allowed more complex and efficient communication and cooperation. This encouraged conceptual thinking and other intellectual skills, again leading to the development of bigger brains.
Modern humans first appeared in Africa around 150,000 – 180,000 years ago; one of a closely-related group of hominids that had populated the savannah over the preceding three million years. During that time, our ancestors learned how to talk, how to make fire and cook and how to cooperate in groups. We probably lived in a similar way to earlier hominids, but something extraordinary happened: we developed culture.