This ridiculous article (shame on the once-great Scientific American) ignorantly misunderstands the nature of the sex binary: “Actual research shows that sex is anything but binary”. Sex is not defined by chromosomes, nor by anatomy, nor by psychology or sociology, nor by personal inclination, nor by “assignment at birth”, but by gamete size. It happens to be embryologically DETERMINED by chromosomes in mammals and (in the opposite direction) birds, by temperature in some reptiles, by social factors in some fish. But it is universally DEFINED by the binary distinction between sperms and eggs. You may argue about “gender” if you wish (biologists have better things to do) but sex is a true binary, one of rather few in biology.