Men have prostates because the gland plays a critical role in reproduction. The prostate produces a nutrient-rich fluid that makes up a significant portion of semen, nourishing and protecting sperm so they can survive long enough to fertilize an egg. Without it, sperm would have a much harder time staying alive and mobile after ejaculation.
What the Prostate Actually Does
The prostate is a small, partly muscular gland that sits just below the bladder, wrapped around the urethra. It has two main jobs: making fluid and pushing it out. The fluid it produces contains enzymes, zinc, and citric acid, all of which help keep sperm cells nourished and the urethra lubricated. During ejaculation, muscles within the prostate contract to force semen through the urethra and out of the body.
Sperm cells themselves are produced in the testicles, but they make up only a small fraction of semen. The rest is a cocktail of fluids from several glands, with the prostate being one of the primary contributors. Those fluids contain calcium, fructose, glucose, magnesium, potassium, and zinc. These nutrients give sperm the energy they need to swim and protect them from the acidic environment inside the vaginal canal, which would otherwise kill them quickly.
How the Prostate Develops
The prostate’s growth is driven almost entirely by hormones, specifically a potent form of testosterone called DHT. During fetal development, DHT triggers the formation of the prostate in the first place. Males born with a genetic condition that prevents their bodies from producing DHT typically have a very small or completely absent prostate, which underscores how essential the hormone is to the gland’s existence.
At puberty, rising DHT levels cause the prostate to grow alongside other reproductive organs. The prostate itself can produce large amounts of DHT locally, which stimulates normal glandular activity. This self-reinforcing loop is why the prostate remains active throughout a man’s life, but it’s also the reason the gland tends to keep growing over time, sometimes causing problems.
Why It Changes With Age
In a man’s 20s, the prostate is roughly the size of a walnut. By 40, it’s often slightly larger. By 60, it can reach the size of a lemon. This continued growth is called benign prostatic hyperplasia (BPH), and it happens because the prostate never stops responding to DHT stimulation, even long after a man’s reproductive years.
Because the prostate surrounds the urethra, this growth can gradually squeeze the tube and make urination slower, more frequent, or harder to start. BPH is not cancer, and it’s extremely common. It’s essentially the downside of having a hormone-responsive gland in a location where any swelling creates mechanical problems. The prostate’s position makes perfect sense for its reproductive role (it needs direct access to the urethra to inject fluid into semen) but becomes a design flaw as the gland enlarges.
Why the Prostate Exists at All
The deeper answer to “why do men have prostates” is that unassisted sperm are fragile. They need protection, fuel, and a liquid medium to travel in. The prostate evolved as a male sex accessory gland that significantly enhances fertility by providing all three. Across mammals, the prostate serves this same basic function: producing secretions that give sperm the best chance of reaching and fertilizing an egg.
In practical terms, men who have their prostates surgically removed (typically due to cancer) become infertile because semen volume drops dramatically and lacks the protective fluid sperm depend on. The body has no backup system for what the prostate does. It’s not a vestigial organ or a biological afterthought. It’s a core part of the reproductive machinery, one that works well for decades but, in many men, eventually becomes a source of medical issues precisely because it never stops doing its job.