One of the crucial differences between males and females pertains to how their reproductive cells, sperm and eggs, are produced.
Males retain precursor sperm cells (known as germline stem cells) within their testis that enable them to produce new sperm via a process known as spermatogenesis throughout their lifetime. The entire process of spermatogenesis lasts around 74-120 days and around 100 million viable sperm are produced every single day!
In stark contrast, females are born with a fixed quota of around 1-2 million eggs. Since no new eggs are produced after birth, the eggs and their surrounding follicles endowed at birth are the sole source of a woman’s eggs as well as the hormones, oestrogen and progesterone, which are produced by follicular cells. Being born with a fixed number of eggs has two important consequences: firstly, eggs undergo ageing which diminishes their quality and, secondly, egg numbers decline with age until they eventually run out resulting in the menopause.