Every male mammal that has ever been examined possesses a prostate gland. From a house mouse to a blue whale, from a wombat to a human, the prostate is a universal feature of the male mammalian reproductive tract. That universality, though, hides enormous variation in shape, size, and even seasonal behavior. The gland can look radically different from one species to the next, and some mammals even have functional prostate tissue in females.
Why Every Male Mammal Has a Prostate
The prostate’s universality comes down to a shared developmental blueprint. During embryonic life, all male mammals form a structure called the urogenital sinus, a common precursor to parts of the urinary and reproductive systems. Under the influence of testicular androgens, tissue surrounding the urogenital sinus sends chemical signals to the lining cells, which then sprout small buds that grow, branch, and eventually become the prostate gland. This process has been described in detail for humans, where it follows a sequence of budding, elongation, branching, and finally the maturation of secretory cells.1PubMed Central. Development of the human prostate In mice, the same basic chain of events takes place, driven by the same androgen-receptor signaling that determines the formation of other male-specific organs like the epididymis and seminal vesicles.2PubMed. Androgens and mammalian male reproductive tract development
The androgen receptor is the molecular gatekeeper. Without a functioning version of it, the prostate simply does not develop, and even in adults, blocking androgen signaling causes the gland to shrink.3PubMed Central. The role of the androgen receptor in prostate development and benign prostatic hyperplasia Because the androgen receptor and the basic urogenital sinus anatomy are conserved across all mammals, the prostate appears in every branch of the mammalian family tree. It is one of the most consistently present accessory reproductive glands in the class.
The Same Gland Looks Very Different Across Species
Saying “all male mammals have a prostate” can be misleading if it conjures the image of a single walnut-shaped organ wrapping around the urethra. That description fits humans reasonably well, but the prostate takes on dramatically different forms in other species. What unifies them is function and developmental origin, not appearance.
In marsupials, the prostate typically has a carrot-like shape with three distinct regions along its length. The hairy-nosed wombat, for example, has this characteristic marsupial prostate along with three pairs of bulbourethral glands, a configuration quite different from the compact gland humans carry.4PubMed. Histology and histochemistry of the accessory reproductive glands in the male hairy-nosed wombat (Lasiorhinus latifrons) In rodents, the prostate is split into several distinct lobes, each with different tissue properties. The rat prostate, for instance, has ventral, dorsal, lateral, and anterior lobes (the anterior lobe is also called the coagulating gland) that differ in their molecular makeup and their roles in reproduction.5PubMed. Nongastric H-K-ATPase in rodent prostate: lobe-specific expression and apical localization
Cetaceans present a particularly interesting case because they have spent tens of millions of years adapting to a fully aquatic life, losing limbs and external ears along the way, yet they still have prostates. Across nine species of toothed whales and dolphins that were examined, the prostate appeared as a muscular-glandular organ with two distinct parts. In the pygmy sperm whale and Cuvier’s beaked whale, the prostate was a compact, discrete gland, while in other species the glandular tissue was more spread out around the urethra.6PubMed Central. Comparative morphology, histology, and cytology of odontocete cetaceans prostates The fact that whales retain a prostate despite the wholesale redesign of their body plan tells you something about how fundamental the gland is to mammalian reproduction.
Dogs have a prostate that sits in roughly the same anatomical position as the human version and shares many functional and physiological features with it.7PubMed Central. Comparative pathology of dog and human prostate cancer This structural similarity is more than a curiosity, as it has made dogs one of the most important animal models for studying human prostate disease.
What the Prostate Does and Why Its Job Description Varies
The prostate contributes fluid to semen. That much is consistent across mammals. But the specific composition and purpose of that fluid shifts depending on the species’ reproductive strategy. In general, prostatic secretions provide nutrients and enzymes that help sperm survive after ejaculation, maintain the right chemical environment for sperm motility, and in some species, play a direct role in the mechanics of mating.
One of the more dramatic examples involves rodents. In rats and guinea pigs, semen rapidly clots inside the female reproductive tract after mating, forming a physical plug that blocks the vaginal opening. This copulatory plug is created when proteins from the seminal vesicles are acted upon by enzymes secreted mainly by the coagulating gland, which is the anterior lobe of the rodent prostate.8PubMed. Transglutaminases and the clotting of mammalian seminal fluids The process is vigorous enough that after mating, a rat’s coagulating glands are nearly emptied of their secretory contents within a few hours.9PubMed. Secretion in the rat coagulating gland (anterior prostate) after copulation This plug-forming function is absent in humans and many other mammals, which illustrates how the same underlying organ can be adapted to serve species-specific reproductive tactics.
Beyond seminal fluid chemistry, the prostate also appears to play a role in local immune defense. In humans, defensins, which are small antimicrobial proteins, are expressed in the prostate gland and detected in semen.10PubMed Central. Defensins: defenders of human reproductive health These proteins help protect the reproductive tract from bacterial infection, adding an immunological function on top of the gland’s primary secretory role.
An interesting pattern connects diet to the rest of the male accessory gland complement. While all male mammals have a prostate, the seminal vesicles, another pair of glands that contribute to semen, are not universal. Carnivorous species like dogs and cats generally lack seminal vesicles, while herbivores and omnivores tend to have them.11PubMed. Similarities of prostate and breast cancer: Evolution, diet, and estrogens The prostate, by contrast, persists regardless of what the animal eats, making it the one reproductive accessory gland that never disappears.
Sperm Competition Shapes Prostate Size
If the prostate’s presence is constant, its size is not. Across rodent species, the relative size of certain accessory reproductive glands scales with the level of sperm competition a species faces. Species where females mate with multiple males, creating intense competition among sperm from different males, tend to have larger seminal vesicles and larger anterior prostates compared to species with lower mating competition.12PubMed Central. Sperm competition and the evolution of male reproductive anatomy in rodents
This makes evolutionary sense. A bigger anterior prostate produces more of the clotting enzymes needed to form a larger or more durable copulatory plug, which reduces the chance that a rival male’s sperm will displace the first male’s. The prostate, in this context, is not just a passive fluid dispenser. It is a weapon in a reproductive arms race, and its size has been shaped by the mating system the species evolved within. This is one of the clearest examples of sexual selection acting on an internal organ rather than an obvious external trait like antlers or a colorful tail.
Seasonal Breeders and the Shrinking Prostate
In mammals that breed only during certain months of the year, the prostate does not simply sit idle during the off-season. It actively shrinks and then regrows in sync with the reproductive cycle. This seasonal plasticity is striking because it means the prostate is not a fixed anatomical fixture but a dynamic organ that remodels itself on a schedule.
The grey squirrel provides a well-documented example. During the breeding season from January through June, its prostate cells are packed with the organelles needed for active secretion. But from July through September, the gland becomes atrophic, with almost all the cellular machinery associated with secretory activity disappearing. Recovery begins in October through December with a wave of cell division that rebuilds the gland before the next breeding season starts.13PubMed Central. Ultrastructural changes in the prostate gland of a seasonally breeding mammal, the grey squirrel (Sciurus carolinensis Gmelin)
A similar cycle has been documented in the raccoon. During months when spermatogenesis declines, the prostate’s glandular lining goes through a regression process where cells slough off into the lumen, followed by restoration as the breeding season approaches again. This cycle is coordinated by changes in androgen receptor expression and cell proliferation within the gland.14Journal of Veterinary Medical Science. Seasonal changes of the prostate gland in the raccoon (Procyon lotor) inhabiting Hokkaido, Japan
Humans, as year-round breeders, do not experience this seasonal demolition and rebuilding. But the underlying capacity for androgen-driven growth and regression is still present, which is why hormone-blocking therapies can shrink an enlarged human prostate. The molecular machinery that allows a squirrel’s prostate to atrophy every summer is essentially the same machinery that a urologist exploits when prescribing medication for benign prostatic hyperplasia.
A Marsupial Twist on Prostate Hormones
The conventional assumption for decades was that testosterone, converted inside cells to a more potent form called dihydrotestosterone, was the androgen responsible for building the prostate during fetal development across all mammals. Research on the tammar wallaby challenged that assumption. In wallaby pouch young, the standard androgens, testosterone and dihydrotestosterone, are present at similar levels in males and females during the period when the prostate is forming, which makes them unlikely candidates for driving male-specific development.
Instead, another androgen, a derivative called 5-alpha-androstane-3-alpha,17-beta-diol, turned out to be produced by the testes and present at higher concentrations in male plasma during early sexual differentiation. When researchers administered this compound to female wallaby pouch young, it induced the formation of prostatic buds, structures that would normally never appear in females. In target tissues, this circulating androgen was converted to dihydrotestosterone, suggesting a two-step process: the testes export a precursor that is then activated locally.15PubMed. Prostate formation in a marsupial is mediated by the testicular androgen 5 alpha-androstane-3 alpha,17 beta-diol
This finding matters because it shows that while the endpoint is always the same, a prostate, different mammalian lineages can use different hormonal routes to get there. The developmental blueprint is conserved, but the specific hormonal signals have diversified over evolutionary time. Marsupials diverged from placental mammals roughly 160 million years ago, and in that time, the proximate endocrine signal shifted even though the outcome did not.
Female Mammals Have Prostate Tissue Too
Perhaps the most counterintuitive piece of the prostate story is that it is not exclusively male. Females of several mammalian species, including humans, have a structure that is developmentally and functionally equivalent to the male prostate. In human anatomy, this tissue is known as the Skene’s gland or paraurethral gland, and for decades it was treated as an obscure anatomical footnote. More recent work has pushed for its recognition as a genuine female prostate.
Ultrastructural examination of the normal adult human female prostate revealed that it contains the same two basic cell types found in the male version: mature secretory cells and basal cells. The study’s authors described it as a functional genitourinary organ, not a vestigial leftover.16PubMed. Ultrastructure of the normal adult human female prostate gland (Skene’s gland) The female prostate has been documented in a range of mammalian species beyond humans, including rodents, rabbits, bats, and dogs. In rodents, the female prostate shows strong similarities to the ventral lobe of the male prostate at both the gross and microscopic levels.17PubMed. Female prostate: historical, developmental, and morphological perspectives
The plains viscacha, a large South American rodent, offers a particularly detailed example. Anatomical study of this species revealed a paraurethral gland formed by glandular units surrounded by connective tissue and smooth muscle fibers, a structural arrangement that mirrors the male prostate’s architecture.18PubMed. Morphological characterization of the female prostate (Skene’s gland or paraurethral gland) of Lagostomus maximus maximus
The female prostate’s existence makes perfect sense embryologically. Both sexes start with the same urogenital sinus precursor tissue. In males, high androgen levels drive full prostatic development. In females, lower androgen levels allow only partial development of the same tissue, resulting in a smaller gland that retains many of the same cell types and secretory capabilities. The wallaby experiment described earlier, where administering an androgen to female pouch young induced prostatic buds, demonstrates that the female body already contains the raw material for a prostate; it just typically does not receive the hormonal signal to build a full-sized one.15PubMed. Prostate formation in a marsupial is mediated by the testicular androgen 5 alpha-androstane-3 alpha,17 beta-diol
Growth Factor Signaling Without Testosterone
Recent experimental work has added a surprising wrinkle to the story of prostate development. Researchers working with mouse tissue managed to induce the formation of prostate buds from urogenital epithelium even in the absence of the surrounding mesenchymal tissue that normally sends the initiating signals. When a specific growth factor, FGF10, was supplied to the isolated epithelium, prostatic budding occurred without testosterone. Adding another signaling pathway on top of FGF10 enhanced the expression of prostate progenitor markers even further.19PubMed. In vitro induction of prostate buds from murine urogenital epithelium in the absence of mesenchymal cells
This does not mean testosterone is irrelevant to prostate formation in a living animal, where it clearly plays a central role. But it suggests that the epithelial tissue lining the urogenital sinus is primed for prostate formation and can be tipped into that fate by growth factor signals alone under the right conditions. In normal development, androgens act on the mesenchyme, which then produces growth factors like FGF10 that instruct the epithelium. The experiment essentially skipped the middleman. Understanding these pathways has practical implications for regenerative medicine and for cancer research, since some of the same signaling circuits that build the prostate during development are reactivated in prostate tumors.
Dogs and Prostate Disease Research
Among all the mammals with prostates, dogs hold a special place in medical research because their prostate develops the same diseases that affect humans. Dogs are one of the few non-human mammals that spontaneously develop prostate cancer with aging, and their version of the disease shares enough anatomical and physiological features with the human form that the canine prostate has been proposed as a translational model for studying the disease in men.7PubMed Central. Comparative pathology of dog and human prostate cancer
Most laboratory rodents, by contrast, do not spontaneously develop prostate cancer, which limits their usefulness for modeling the disease as it actually occurs in aging humans. The multi-lobed rodent prostate also makes direct anatomical comparisons tricky, since there is no clean one-to-one correspondence between a rat’s ventral prostate lobe and the zones of the human prostate that clinicians care about. Dogs bridge that gap. Their prostate sits in the same pelvic position, responds to the same hormones, and develops age-related enlargement and malignancy through pathways that overlap substantially with those in humans. For researchers trying to test new therapies or understand why some prostates become cancerous and others do not, dogs offer a naturally occurring version of the problem rather than a genetically engineered one.