"The International Olympic Committee (IOC) introduced sex testing in 1968 at the Olympic games in Mexico City, after the masculine appearance of some competitors, many pumped up by anabolic steroids, had started to raise questions about the gender of athletes in female events. Unsurprisingly, gender-determination tests were seen as degrading, with female competitors having to submit to humiliating and invasive physical examinations by a series of doctors. Later, the IOC decided to use a supposedly more sophisticated genetic test, based on chromosomes. Women usually have two X chromosomes; men an X and a Y chromosome. So, according to the rules of the test, only those athletes with two X chromosomes could be classed as women. However, many geneticists criticised the tests, saying that sex is not as simple as X and Y chromosomes and is not always simple to ascertain.
It is thought that around one in 1,000 babies are born with an "intersex" condition, the general term for people with chromosomal abnormalities. It may be physically obvious from birth - babies may have ambiguous reproductive organs, for instance - or it may remain unknown to people all their lives. At the Atlanta games in 1996, eight female athletes failed sex tests but were all cleared on appeal; seven were found to have an "intersex" condition. As a result, by the time of the Sydney games in 2000, the IOC had abolished universal sex testing but, as will happen in Beijing, some women still had to prove they really were women."