Why Do Men Have Nipples? The Evolutionary Science Behind This Quirky Male Trait

Have you ever noticed that men have nipples? Like, what’s up with that? Unlike women, men can’t breastfeed babies. So why bother having nipples at all?

It’s a perfectly valid question that speaks to the quirky, imperfect ways human bodies evolve. As it turns out, there are some fascinating biological reasons men retain these seemingly useless body parts. Let’s unravel the science behind why guys have nipples!

Nipples Start Developing Before Embryos Become Male or Female

The key to understanding why men have nipples lies in how humans develop in the womb. For the first several weeks of gestation, a developing embryo follows a “default” template for what will become a human body.

During this early stage, the embryo is neither distinctly male nor female. Its genes haven’t yet activated the instructions to start specializing cells into male or female anatomy.

So early on, the embryonic tissue begins budding what will eventually become nipples and breast tissue in both sexes. It takes several weeks before the sex chromosomes kick in and start driving development towards male or female structures.

By the time the Y chromosome activates to make the fetus develop into a male, the nipples have already started forming. Evolution simply never selected for a process to halt nipple development in males.

There’s No Evolutionary Pressure to Remove Useless Male Nipples

Evolution works by selecting for advantageous traits and discarding detrimental ones. But male nipples seem to fall in a quirky middle ground. They don’t help or harm survival and reproduction.

If a trait doesn’t affect an organism’s chances of living long enough to pass on its genes, there’s no pressure from natural selection to remove it. Useless traits simply tag along in the genome unselected for or against.

Male nipples are like biological free riders. We can think of them as largely functionless vestiges, like our wisdom teeth or appendix. They neither help nor hurt the human body enough to evolve one way or another.

Since nipples pose no clear evolutionary disadvantage to males, natural selection allows them to persist from our early developmental structures.

Men’s Nipples Still Serve a Sensual Purpose

While men’s nipples don’t provide milk, they aren’t entirely useless. The nipple tissue remains sensitive and wired for sensual stimulation. So men are still able to derive sexual pleasure from this breast anatomy.

When stimulated, nerves send signals to the brain’s sensory cortex, releasing feel-good neurotransmitters like dopamine and oxytocin. So men can thank women for helping select for pleasurable nipple sensitivity over our evolutionary past.

Male and Female Bodies Default to Shared Traits

Another way to think about why men have nipples is to understand that male and female bodies don’t start from scratch. Our genomes don’t contain separate instructions for male and female structures.

Instead, the default body plan is female. The Y chromosome then overrides certain developmental pathways to masculinize the fetus. But any shared traits that don’t interfere with this process, like nipples, remain intact.

So while men’s nipples lie dormant, they still physically exist on male bodies. They are remnants of the default template from which both sexes emerge.

Men Can Sometimes Produce Milk Too

Now, it’s extremely rare, but men can sometimes produce milk from their nipples. This can happen if high levels of prolactin hormone are present, which normally stimulates milk production in women after pregnancy.

In fact, prolactin levels rise in both men and women during sexual stimulation and orgasm. Occasionally this allows men to express a milky discharge. Some male medical conditions or hormone treatments can also cause lactation.

There are accounts throughout history of male wet nurses providing milk for orphaned infants. And some impoverished fathers without access to formula have managed to breastfeed their babies.

So while not a common capability, the mammary glands and milk ducts in men’s chests can retain functionality given the right circumstances.

Male Nipples Still Require Some Medical Consideration

Since men have breast tissue and ducts, they can still develop medical conditions that affect these structures. While extremely rare, men can get breast cancer. Male nipple discharge or pain could indicate an underlying health issue requiring examination.

During the embryonic stage, the mammary ridge that becomes nipples and breast tissue develops separately from the gonads that become ovaries or testes. So even though men don’t need mammary glands to feed offspring, they carry this legacy anatomy forward.

The Takeaway: Our Bodies Are Imperfect Products of Evolution

At the end of the day, we’re left with the simple conclusion that men have nipples as an evolutionary artifact. Without any selective pressures acting on the trait, it persists as a leftover from early development in the womb.

Our bodies are imperfect products of gradual evolution, not intelligent designs created from scratch. So we’re left with quirky, useless parts like male nipples and appendixes.

These peculiar body parts speak to the winding path our evolution has taken. While we may look designed, our imperfections reveal we are continually adapting products of natural selection. Our human anatomy has many flaws and inefficiencies that we’ve accumulated along the way.

So the next time you notice a man’s nipples, take a moment to appreciate how evolution tinkers, meanders and pieces together new biological forms. Our bodies have many stories to tell if you know where - and on whom - to look!