Men do not have ovaries. The typical male body contains testes, not ovaries, and the two organs develop from the same undifferentiated tissue during the first weeks of embryonic life. What steers that tissue toward becoming testes rather than ovaries is a single gene on the Y chromosome, and understanding that fork in the road explains not only why men lack ovaries but also why rare exceptions exist and what they reveal about how sex development actually works.
Every Embryo Starts With the Same Reproductive Blueprint
For roughly the first six weeks after conception, the gonads of every human embryo are identical regardless of chromosomal sex. These early structures are called bipotential gonads because they have the capacity to become either testes or ovaries. At this stage the embryo also has two sets of internal ducts: the Wolffian ducts, which can develop into male structures like the vas deferens and epididymis, and the Müllerian ducts, which can develop into the uterus, fallopian tubes, and upper vagina. Every embryo carries both sets of ductwork, waiting for signals that will preserve one and dismantle the other.
The bipotential gonad expresses a shared set of markers during this window. Laboratory research mimicking this process in cell culture has confirmed that early gonadal tissue upregulates the same set of genes regardless of whether it will eventually become testicular or ovarian tissue.1PubMed Central. An In Vitro Differentiation Protocol for Human Embryonic Bipotential Gonad and Testis Cell Development This shared starting point is why male and female reproductive organs have so many structural parallels: the testes and the ovaries are not unrelated organs that happen to exist in different bodies. They are two outcomes of the same primordial tissue, shaped by different molecular instructions.
The Genetic Switch That Makes Testes Instead of Ovaries
The decision point hinges on a gene called SRY, located on the Y chromosome. SRY encodes a protein that binds to DNA and kicks off a cascade leading to testis formation. Its main downstream target is another gene called SOX9. Research has shown that SRY works together with a co-factor called SF1 to activate a specific enhancer region of SOX9, and once SOX9 protein is produced, it loops back and helps maintain its own expression even after SRY activity fades.2PubMed. Sex determination involves synergistic action of SRY and SF1 on a specific Sox9 enhancer This self-reinforcing loop locks the gonad into a testicular fate.
SRY’s role is specifically to trigger the differentiation of supporting cells within the gonad into Sertoli cells, the cells that organize testis structure and nurture developing sperm. Without SRY, those same supporting cell precursors would instead become follicle cells and help form an ovary.3PubMed. Balancing the bipotential gonad between alternative organ fates: a new perspective on an old problem The process is sometimes described as a tug-of-war: pro-testis and pro-ovary genetic pathways are both active in early development, and the gonad commits to one direction only when one pathway gains enough momentum to suppress the other. SRY tips the balance decisively toward testis.
Importantly, SRY does not act by itself in a vacuum. It requires SF1 to co-activate SOX9 expression, and SRY’s binding to the testis-specific enhancer of SOX9 is a critical step that has been confirmed through direct biochemical studies.4PubMed. SRY: A transcriptional activator of mammalian testis determination If SRY is absent, non-functional, or if any step in this cascade fails, the gonad develops along the ovarian pathway by default.
How the Male Body Dismantles Its “Female” Ductwork
Once the testes form, they produce two hormones that reshape the embryo’s internal plumbing. The Sertoli cells secrete anti-Müllerian hormone (AMH), which causes the Müllerian ducts to regress. This happens during a narrow window: AMH expression begins around eight weeks of gestation, and by about nine weeks the Müllerian ducts have undergone irreversible regression.5The Journal of Clinical Endocrinology & Metabolism. Clinical Utility of Anti-Mullerian Hormone in Pediatrics – Section: Physiological Role of AMH Without functional Müllerian ducts, the structures that would have become the uterus and fallopian tubes simply disappear.
At the same time, the fetal Leydig cells in the testes produce testosterone, which stabilizes and promotes the differentiation of the Wolffian ducts into the epididymis, vas deferens, and seminal vesicles.6Biology of Reproduction. Functional Redundancy of TGF-beta Family Type I Receptors and Receptor-Smads in Mediating Anti-Müllerian Hormone-Induced Müllerian Duct Regression in the Mouse Wolffian duct differentiation depends on androgen signaling rather than on sex chromosomes directly. Research in animal models has shown that this androgen action must happen within a specific fetal programming window, estimated at roughly eight to twelve weeks of gestation in humans, and disrupting androgen receptor activity during this period prevents the Wolffian ducts from developing properly.7Biology of Reproduction. A tale of two tracts: history, current advances, and future directions of research on sexual differentiation of reproductive tracts – Section: How do androgens promote the maintenance of Wolffian ducts?
So the typical male outcome is a body with testes, Wolffian-derived structures, and no trace of the Müllerian ducts. This is why men do not have ovaries, a uterus, or fallopian tubes: the genetic cascade starting with SRY leads to testes, which produce hormones that actively eliminate the precursor structures for female reproductive organs.
Persistent Müllerian Duct Syndrome
In rare cases, the system breaks down at the hormone level rather than the genetic one. In persistent Müllerian duct syndrome (PMDS), a person has a Y chromosome, typical male external genitalia, and functioning testes, but also retains a uterus and fallopian tubes internally. This happens because either AMH was not produced in sufficient quantity or the receptors that respond to AMH did not work correctly, so the Müllerian ducts were never given the signal to regress.8PubMed Central. Persistent mullerian duct syndrome
PMDS is classified as a rare form of internal male pseudohermaphroditism. The condition is familial in some cases, and genetic studies of affected families have traced it to defects in either the AMH gene itself or the gene encoding its receptor.9Human Molecular Genetics. Molecular genetics of the persistent Müllerian duct syndrome: a study of 19 families People with PMDS are typically raised as boys and may not discover the retained Müllerian structures until they undergo surgery for something else, often for undescended testes. One recent case report described PMDS being discovered incidentally in a male patient being treated for bilateral cryptorchidism and a testicular tumor.10PubMed Central. Incidental Discovery of Persistent Müllerian Duct Syndrome in a Male With Bilateral Cryptorchidism and a Testicular Germ Cell Tumor: A Rare Case Report
Even in PMDS, the person still has testes rather than ovaries. The gonads differentiated correctly under SRY’s influence; the issue is limited to the duct system. The retained uterus and fallopian tubes are usually non-functional, and the person’s hormonal profile is that of a typical male. PMDS demonstrates that sex development is not a single switch but a series of steps, each of which can succeed or fail somewhat independently.
When Both Ovarian and Testicular Tissue Exist in One Body
There is one condition in which a person can genuinely have ovarian tissue alongside testicular tissue: ovotesticular disorder of sex development (OT-DSD), historically called “true hermaphroditism.” This is the rarest form among all disorders of sex development and involves the simultaneous presence of both ovarian tissue containing primordial follicles and testicular tissue containing seminiferous tubules.11PubMed Central. Ovotesticular Disorder of Sex Development: An Unusual Presentation The two tissue types can exist in the same gonad (called an ovotestis) or in separate gonads on different sides of the body.12V.F.Snegirev Archives of Obstetrics and Gynecology. Ovotesticular disorder of sex development: bilateral ovotestes (clinical case)
Individuals with OT-DSD typically present with ambiguous genitalia in infancy, and the condition can occur across a range of chromosomal backgrounds. The testicular tissue may have variable fertility potential, while the ovarian tissue contains follicles at various stages.13PubMed Central. Ovotesticular Disorder of Sex Development: Approach and Management of an Index Case in the Dominican Republic OT-DSD challenges the simple binary of “ovaries or testes” because it shows the bipotential gonad can, in rare circumstances, partly commit to both fates at once. These individuals are not typically described as “men with ovaries” or “women with testes” since their sex development diverged from the typical male or female path early on, and the clinical picture varies enormously from person to person.
Chromosomal Combinations That Defy Expectations
The link between chromosomes and reproductive organs is strong but not absolute. Two conditions illustrate the exceptions particularly well.
In 46,XX testicular DSD (sometimes called XX male syndrome), a person has two X chromosomes and no Y chromosome yet develops testes and typical male external genitalia. This usually happens because a small piece of the Y chromosome carrying SRY has been translocated onto one of the X chromosomes during sperm formation. The majority of affected individuals present as phenotypically normal males with normal external genitalia.14Journal of Clinical and Translational Endocrinology: Case Reports. A case report of hypogonadism and infertility in 46,XX (SRY positive) male syndrome – Section: Discussion They have testes, not ovaries, because SRY was present and functional even without a full Y chromosome. Most learn of the condition only when they experience infertility or are evaluated for small testicular volume.
The mirror image is Swyer syndrome, or 46,XY gonadal dysgenesis. Here a person has X and Y chromosomes but SRY is mutated or absent, so the gonads never receive the signal to become testes. Instead of developing ovaries, the gonads remain as non-functional “streak” tissue. People with Swyer syndrome have female external genitalia and develop a uterus and fallopian tubes (because no AMH was produced to cause regression), but the uterus is typically underdeveloped and they do not go through spontaneous puberty because the streak gonads produce neither estrogen nor testosterone in meaningful amounts.15PubMed Central. Swyer syndrome in a woman with pure 46, XY gonadal dysgenesis and a hypoplastic uterus Swyer syndrome makes an important point: having a Y chromosome does not guarantee testes. Without a working SRY gene, the gonad does not commit to either a testicular or a fully functional ovarian fate.
How Diagnosing These Conditions Works
Most differences in sex development are identified either at birth (when genital appearance is atypical), during puberty (when expected changes do not occur), or incidentally during unrelated surgery. The diagnostic workup typically combines a thorough physical examination with hormone level testing, chromosomal analysis, and imaging of the genitourinary tract.16PubMed. Evaluation and management of disorders of sex development: multidisciplinary approach to a complex diagnosis Ultrasound can reveal internal structures like a uterus that might not be expected, while blood tests for AMH, testosterone, and other hormones help clarify whether the gonads are functioning as testes, ovaries, or something in between. Genetic testing can identify whether SRY is present and whether AMH or its receptor gene carries mutations.
The move toward multidisciplinary care teams, including endocrinologists, surgeons, geneticists, and psychologists, reflects how complex these conditions are. No single test provides the full picture, and treatment decisions often need to account for the person’s gender identity, fertility goals, and risk of gonadal tumors (streak gonads in Swyer syndrome, for instance, carry an elevated cancer risk and are usually removed).
Environmental Chemicals and Male Reproductive Development
The fetal programming window during which testes form and begin producing hormones is sensitive to outside interference. Endocrine-disrupting chemicals (EDCs), substances that mimic or block hormones, can interfere with the tightly regulated pathways of sexual differentiation. In males, disrupted androgen signaling during fetal development has been linked to conditions including hypospadias, cryptorchidism, reduced fertility, and testicular cancer.17PubMed. Endocrine-disrupting chemicals and reproductive health: With focus on the developmental window of susceptibility
Certain phthalates, chemicals found in plastics and personal care products, have received particular attention. Animal studies have shown that fetal exposure to specific phthalates can impair the hormone production of the developing testes, leading to a cluster of abnormalities sometimes grouped under the label “testicular dysgenesis syndrome.”18PubMed. Pathways of endocrine disruption during male sexual differentiation and masculinization The relevance to the ovary-versus-testis question is indirect but real: these chemicals do not cause ovaries to form in a male embryo, but they can compromise how well the testes develop and function, blurring some of the downstream hormonal distinctions that typically separate male from female physiology.
Sex Determination Across the Animal Kingdom
The mammalian system, in which a Y-linked gene triggers testis formation and its absence leads to ovaries, is far from universal. Across vertebrates, an enormous diversity of sex determination mechanisms exists, ranging from purely genetic systems to environmental triggers like temperature. Some fish species even undergo functional sex change during adulthood, transitioning from one sex to the other complete with gonadal reorganization.19PubMed. Sex determination, gonadal sex differentiation, and plasticity in vertebrate species
Mammals sit at the most rigid end of this spectrum. Once the gonad commits to a testicular or ovarian fate, the decision is essentially irreversible under natural conditions. There is no equivalent in humans or other mammals of the clownfish’s ability to switch from male to female when the dominant female in a group dies. The self-reinforcing genetic loops that lock in testis development, like the SOX9 feedback mechanism described earlier, make mammalian gonadal sex stable in a way that many other vertebrate species’ gonadal sex is not. This rigidity is part of why conditions like OT-DSD are so extraordinarily rare in humans: the molecular machinery is strongly biased toward committing fully to one gonadal type.
Can Ovarian Tissue Function in a Male Body?
An intriguing experimental question is whether ovarian tissue can survive and function when transplanted into a male hormonal environment. Mouse research has tested this by transplanting frozen-thawed ovarian tissue subcutaneously into adult male mice. The results showed that follicles within the transplanted tissue survived and developed regardless of the recipient’s baseline hormonal environment.20Reproductive and Developmental Medicine. Offspring from oocytes grown in frozen-thawed ovarian tissues transplanted to male and female bodies This is strictly laboratory work in mice, not a clinical possibility for humans, but it demonstrates that ovarian tissue is not inherently incompatible with a male body. The tissue needs hormonal support to function (follicle development requires certain hormone signals), but the male endocrine environment does not destroy the tissue outright.
Separately, studies of transmasculine individuals who take testosterone have examined what happens to existing ovarian tissue in a body with elevated androgen levels. A multicenter case series found that ovarian pathology in these patients remained benign while on testosterone, with follicle development and simple cysts falling within the normal range for reproductive-age ovaries. None of the ovaries in the study showed pathology that would have required surgical removal.21PubMed Central. Ovarian Histopathology in Transmasculine Persons on Testosterone: a multicenter case series – Section: Discussion These findings are relevant to transgender healthcare decisions around whether oophorectomy is medically necessary during gender-affirming surgery and suggest that ovarian tissue does not become dangerous simply because the surrounding hormonal milieu is androgenic.
Neither of these lines of research means that a typical man “has” or “could have” ovaries in any practical sense. But they fill in a subtler picture: the gonads are less rigidly bound to one hormonal context than people tend to assume, and ovarian tissue is more resilient across different endocrine environments than its reputation might suggest.