Custer Semen, South African Woman Runner

Biological factors are not sufficient determinants of whether a person considers herself a woman or is considered a woman. Intersex individuals, who have mixed physical and/or genetic features, may use other criteria in making a clear determination. There are also transgender or transsexual women, who were born or physically assigned as male at birth, but identify as women; there are varying social, legal and individual definitions with regard to these issues.
Although fewer females than males are born (the ratio is around 1:1.05), due to a longer life expectancy there are only 81 men aged 60 or over for every 100 women of the same age. Women typically have a longer life expectancy than men. This is due to a combination of factors: genetics (redundant and varied genes present on sex chromosomes in women); sociology (such as not being expected in most countries to perform military service); health-impacting choices (such as suicide or the use of cigarettes, and alcohol); the presence of the female hormone estrogen, which has a cardioprotective effect in premenopausal women; and the effect of high levels of androgens in men. Out of the total human population, there are 101.3 men for every 100 women (source: 2001 World Almanac).
Most women go through menarche and are then able to become pregnant and bear children. This generally requires internal fertilization of her eggs with the sperm of a man through sexual intercourse, though artificial insemination or the surgical implantation of an existing embryo is also possible. The study of female reproduction and reproductive organs is called gynaecology.
There are some diseases that primarily affect women, such as lupus. Also, there are some sex-related illnesses that are found more frequently or exclusively in women, e.g., breast cancer, cervical cancer, or ovarian cancer. Women and men may have different symptoms of an illness and may also respond differently to medical treatment. This area of medical research is studied by gender-based medicine.