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

• 核心主张：在每个有两种不同大小性细胞的物种中，恰好有两种性别，因为雄性意味着身体被构造成产生精子，雌性意味着被构造成产生卵子，而不是染色体、激素或身体特征。
• Wright区分了性别如何发育（这在各物种之间差异很大）和性别是什么，并认为许多混淆来自把二者混为一谈。
• 他回答了五项挑战：真菌的“交配型”、额外或缺失的性染色体（如XXY）、被描述为光谱的性发育差异、基于一组特征的定义，以及把性别分为遗传、激素和身体“层面”的模型。
• 关于性发育差异，他认为双性别观点并不要求每个人都能被清楚地分类；不明确的情况并不构成第三种性别，因为它们不会产生第三种性细胞。
• 他称特征集群模型和多层面模型是循环论证，因为特征被标为“典型男性”或“典型女性”，只是通过观察已经按精子或卵子分好类的身体。
• 该文发表于2025年11月（第54卷，第3941-3945页），位于“有多少种性别？有多少种性别认同？”专栏；Dana Mahr于2026年1月发表了批评，Wright于2026年3月作了回应。

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.