howlsmovingcastle84 wrote - "The first thing we tell our students when they start their degree is-do not use Wikipedia as a reference, ever!"
Wikipedia can still be a very useful source of sources.
The Wikipedia article about "Sex" cites multiple peer-reviewed sources that support the biological mainstream idea that there are only two biological sexes in humans, e.g. Proceedings: Biological Sciences, and Seminars in Cell and Developmental Biology. The first sentence of the article even cites the Oxford English Dictionary's long-established biology-based binary definition of sex.
The only mention of sex spectrum that I found in Wikipedia's article about "Sex" is in its "Further reading" section that merely lists an article titled "Sex redefined: The idea of two sexes is simplistic. Biologists now think there is a wider spectrum than that". This spectrum article was was published in "Nature", which is a major scientific journal.
Rubbish is published in allegedly reputable sources much more often than is generally acknowledged by university staff, so students should treat all sources with care, even if university staff lull their students into a false sense of security by rubbishing Wikipedia while giving other sources the "all clear".