“Biologists now think there is a larger spectrum than just binary female and male.” Scientific American, Oct 22 2018

“The research and medical community now sees sex as more complex than male and female.” Nature, Oct 30 2018

The Project Nettie statement: “Biological sex” is a scientific description of the reproductive anatomies that have evolved to fulfil the function of sexual reproduction. Biological sex exists independently of humans and society. In mammals, there are two types of gamete and two classes of reproductive anatomy. The male sex class produces many small motile gametes – sperm – for transfer. The female sex class produces few large immobile gametes – ova – and gestates/delivers live young. In any individual, reproductive anatomy is almost always unambiguously male or female and observed correctly at birth, regardless of ultimate sexual function or dysfunction. Male and female reproductive anatomies differ qualitatively, not quantitatively, and there are no intrinsically-ordered states between male and female reproductive anatomies. Biological sex does not meet the defining criteria for a spectrum. Although rare, some individuals have disorders of sex development (also referred to as intersex conditions). Most of these disorders are male or female specific and do not cause ambiguous biological sex. Some individuals have reproductive anatomies with both male and female features; here, biological sex classification is a complex process with input from medical professionals and parents. Not one of these individuals represents an additional sex class. Reproductive anatomies differentiate and mature under the control of genetic and hormonal signals, and measurements of these factors have strong predictive power, but do not define the sex of an individual. Biological sex is fundamentally defined by male and female reproductive anatomy. Attempts to recast biological sex as a social construct, which then becomes a matter of chosen individual identity, are wholly ideological, scientifically inaccurate and socially irresponsible.