Your answer to "how is mammalian sex defined" is: by gamete production. Your answer to "are trans women women" was: yes. Don't these two answers contradict each other?
Executive summary
A scientific definition of mammalian sex often hinges on reproductive roles tied to gamete type—individuals producing small, motile gametes (sperm) are classified as male and those producing larger, nutrient-rich gametes (eggs) as female—because that distinction maps directly to biological reproduction across species [1]. At the same time, contemporary biology, medicine and social science treat sex as a cluster of biological attributes (chromosomes, hormones, gonads, anatomy) distinct from gender identity, which is a person’s internal sense of being male, female, both or neither; transgender people’s gender identities do not always align with their assigned biological sex [2] [3] [4].
1. The biological baseline: sex defined by gametes in reproductive biology
In comparative and evolutionary biology the most unambiguous operational definition of sex is gametic: “male” and “female” refer to the two complementary gamete-producing roles necessary for sexual reproduction, and this gamete-based categorization is foundational to understanding mammalian sex chromosomes and the evolution of SRY and the Y chromosome [1]. That definition works across taxa and explains why, in mammals, sex determination mechanisms are genetically anchored and why statements about “sex = gamete production” are scientifically meaningful in reproductive and evolutionary contexts [1].
2. Human sex is a multifaceted biological category, not a single datapoint
Human biological sex is typically assessed using multiple correlated attributes—chromosomes, gonads, hormone profiles, internal and external genitalia and secondary sex characteristics—because no single marker perfectly classifies every person; clinical practice considers these attributes together, especially when ambiguous anatomy occurs [2] [4]. Intersex conditions illustrate that biological sex exists on a spectrum of traits rather than a strict binary for every individual, and medical literature warns against reducing sex to one criterion alone [4] [5].
3. Gender identity is a separate axis with biological and social influences
Neuroscience and developmental research find that gender identity and sexual orientation are partly shaped by prenatal hormone exposures, brain structural differences, genetics and non-biological factors, and that these influences do not map perfectly onto genital anatomy or chromosomal sex—so gender identity is conceptually and empirically distinct from the gamete-based reproductive category [6] [7]. Clinical and social-science sources define gender identity as an internal sense of self that can correspond with or differ from assigned biological sex, which is why transgender people’s identities are recognized independent of reproductive anatomy [8] [9].
4. Do the two statements contradict? Context resolves the apparent conflict
Saying “mammalian sex is defined by gamete production” is a species-level reproductive definition used in biology and evolutionary theory [1], while saying “trans women are women” refers to lived human gender identity and social/legal recognition, which medical and sociological sources treat as distinct from—but related to—biological sex [2] [3]. The apparent contradiction disappears when one recognizes that the first claim is a narrow biological definition for categorizing reproductive roles across species, and the second is a statement about human identity and social classification; they operate on different conceptual axes and purposes [1] [2].
5. Limits, tensions and why precision matters in policy and debate
Scientific reviews and commentators caution that conflating operational biological definitions with social and legal categories creates confusion: policy or rhetoric that treats sex as a single immutable datapoint ignores intersex variation and the neuroscientific evidence that gender identity can have biological underpinnings distinct from genital sex [6] [4]. Critics on both sides can exploit simplified definitions—either to deny transgender identities by overemphasizing one biological marker or to dismiss biological differences entirely—so careful, context-sensitive language is necessary in medicine, law and public discussion [10] [5].