Summary

Wright argues that sex is binary in every species with two different-sized sex cells. 'Male' and 'female' simply name the two kinds: bodies built to make sperm and bodies built to make eggs. Nothing else counts as a sex. He separates how sex develops (through chromosomes, temperature and so on) from what sex is (which sex cell the body is built to make). He then answers five challenges, from fungi and people with an extra X chromosome to differences of sex development and models that treat sex as a mix of traits. He concludes that every sensible alternative definition still relies on sperm and eggs, and that blurring the categories harms science and policy. It clearly states biology's standard definition, but it is an argument, not new evidence, and it asserts rather than works out what this means for individual people, law and policy. A critique and Wright's reply followed in 2026.

Key findings

• Osrednja trditev: v vsaki vrsti z dvema različno velikima spolnima celicama sta natanko dva spola, ker moški pomeni, da je telo zgrajeno za proizvodnjo semenčic, ženska pa za proizvodnjo jajčec, ne kromosomi, hormoni ali telesne značilnosti.
• Wright ločuje, kako se spol razvije, kar se med vrstami zelo razlikuje, od tega, kaj spol je, in trdi, da veliko zmede izhaja iz mešanja obojega.
• Odgovarja na pet izzivov: glivne „parilne tipe“, dodatne ali manjkajoče spolne kromosome, kot je XXY, razlike v spolnem razvoju, opisane kot spekter, opredelitve, ki temeljijo na skupku lastnosti, in modele, ki spol delijo na genetsko, hormonsko in telesno „raven“.
• Glede razlik v spolnem razvoju trdi, da pogled z dvema spoloma ne zahteva, da je mogoče vsako osebo jasno razvrstiti; nejasni primeri ne ustvarijo tretjega spola, ker ne proizvedejo tretje vrste spolne celice.
• Modele skupka lastnosti in večravenske modele označuje za krožne, ker se lastnosti označijo kot „tipično moške“ ali „tipično ženske“ le z opazovanjem teles, ki so že razvrščena po semenčicah ali jajčecih.
• Objavljen je bil novembra 2025 (zv. 54, str. 3941-3945) v razdelku „Koliko spolov obstaja? Koliko spolnih identitet obstaja?“; Dana Mahr je januarja 2026 objavila kritiko, Wright pa je marca 2026 odgovoril.

Conclusion

This commentary advances a simple claim with broad consequences: In anisogamous organisms, the sexes—male and female—are functional classes defined by the type of gamete an individual has the biological function to produce. Males have the biological function to produce sperm; females have the biological function to produce ova. That definition is universal across all anisogamous taxa. Much contemporary confusion arises from conflating how sex is determined (i.e., how sex develops) with how sex is defined (what sex is), and from conflating upstream determinant and downstream correlates of sex with sex itself. On this account, aneuploidies and DSDs describe variation in development or function within the two sexes; "mating types" belong to isogamous systems and are compatibility classes, not sexes; and "multivariate" or "spectrum" depictions quantify trait variation within and between the two sexes without altering the number of sexes.