One of the world's most prominent atheists has sided with Christians and traditionalists in the debate over gender by asking his followers to sign a document that declares the "meaning of the word 'woman'" should not "be changed to include men."

Richard Dawkins, a well-known atheist and biologist and the author of The God Delusion, tweeted a link to The Declaration on Women's Sex-Based Rights, which was launched by a United Kingdom group that believes replacing "sex" with "gender identity" would result in "discrimination against women and girls." Although the document implicitly supports legalized abortion and progressive beliefs about sexual orientation, it also promotes traditional beliefs about gender and gender identity.

"Please sign the Declaration on Women's Sex-based Rights. I have just done so," Dawkins tweeted. The same day, Dawkins retweeted a link to a story criticizing the International Olympic Committee for dropping the requirement that transgender women - that is, biological men who identify as female - suppress testosterone levels in their blood.

Men cannot become women, the declaration says.

"Men who claim a female 'gender identity' are being enabled to access opportunities and protections set aside for women," the declaration says. "This constitutes a form of discrimination against women, and endangers women's fundamental rights to safety, dignity and equality.

The declaration takes a firm stance against biological men competing in women's sports even if they identify as female.

"When men claiming female 'gender identities' are enabled to participate in women's single-sex sporting activities, women are placed at an unfair competitive disadvantage and may be placed at increased risk of physical injury," the declaration says. "This undermines women's and girls' ability to have the same opportunities as men to participate in sports, and therefore constitutes a form of discrimination against women and girls, which should be eliminated."

The document also says, "there is no objective scientific evidence" that children are born transgender.

Governments should make clear, the declaration says, that the word "woman" references only biological women.

"The meaning of the word 'woman' shall not be changed to include men," it says.

It's not the first time Dawkins has made his views on gender identity known - although the declaration details them in ways he previously had not done. In 2015, he said, "Is trans woman a woman? Purely semantic. If you define by chromosomes, no. If by self-identification, yes. I call her 'she' out of courtesy."