When Anton van Leeuwenhoek, the Dutch scientist who invented the early compound microscope, first discovered sperm in 1677, he was mortified. He dubbed the swimmers he found in ejaculate, which he’d been begged by his peers and friends to examine, “animalcules” and buttressed groundbreaking work with gothic apologies. He was specifically embarrassed because he did not know at the time if the sperm in the ejaculate he was examine — his own — was unusual.
“If your Lordship should consider that these observations may disgust or scandalise the learned, I earnestly beg your Lordship to regard them as private and to publish or destroy them as your Lordship sees fit,” wrote Leeuwenhoek to the Royal Society of London accompanying his work. The Society opted to publish his findings in 1678 and Leeuwenhoek was rightly lauded for his breakthrough. Still, there was much that both the dutch scientist and his English publishers did not know. Sperm were initially understood to be “preformists,” vessels containing tiny babies. Today, most adults likely know that’s not the case, but even would-be parents struggle to understand how precisely sperm works.
Why the confusion? For one thing, sperm behavior and composition is complicated. For another, human reproduction remains a difficult field of study because new work is often misrepresented, politicized, or misunderstood by people uncomfortable asking follow-up questions. Unfortunately, what we don’t know about sperm could hurt us. The sperm quality of western men is in rapid decline according to knew data. There is, in short, a sperm crisis going on. But to understand that crisis, people must understand how and why swimmers swim.
What the Hell Are Sperm?
First and foremost, sperm is not the same as semen though sperm are a component of semen. Sperm are tiny, streamlined cells with a single set of chromosomes, a head, neck, midpiece, and flagellum, a tail that propels the cells towards the egg and give it its tadpole-like appearance. The head contains a nucleus tightly packed with DNA as well as enzymes that help to penetrate the egg. These enzymes are located in the acrosome on top of the head, like a hat. Sperm without hats cannot gain access to an egg.
How Are They Made?
Sperm is produced in the testicles through a combination of mitosis (cell division that results in two additional cells with the same number and kind of chromosomes as the original) and meiosis (cell division that results in four additional cells with half the number of chromosomes as the original). The process is known as spermatogenesis and takes roughly 74 days. Sperm is stored in the epididymis, a tube connecting the testicles — via a somewhat roundabout route — to the penis and expelled during ejaculation.
Sperm Collaborates With the Egg
Unlike the egg, which provides substantial amounts of genetic material to aid in growth and development, sperm are optimized for efficiency and “exploit” this maternal investment, research shows. In essence, sperm are very efficient packaging for DNA being dropped off. Put another way, sperm supply information software, but play little role in the creation of hardware.
It’s a Volume Game
Men ejaculate anywhere from a half to a full teaspoon of semen per orgasm, which contains about a million sperm. While this may make some eggs seem less greedy, but it’s incredibly difficult for even healthy sperm to make it through the vagina, fallopian tubes and to the egg. Scientists suspect this is natural selections way of making sure only the healthiest sperm get to make babies. Thus, you can have 999,999 problems without infertility being one.
Still, more semen is not necessarily a good thing. Less than a half a teaspoon of semen may not have enough sperm to fertilize the egg, but more than a teaspoon could dilute sperm with excess seminal fluid and cause fertility problems. Interestingly, the condition, known as hyperspermia, often occurs in men with higher sex drives. So, if you’re not the horniest guy, you still could be the most virile.
Sperm Live Longer Than Some Insects
Sperm can survive in the female reproductive tract for up to five days, while mayflies only live for 24 hours. Although this may make sperm seem like the unwanted couch-surfers of conception, in rare instances it can actually cause a woman to become pregnant twice, without having twins in a traditional sense, otherwise known as superfetation. Take that, mayflies.
Sperm Can and (and Often Does) Mutate
Part of the reason men need a million sperm in order to fertilize one egg is that only 4 to 15 percent of sperm are considered normal. The rest of them mutate due to age, environmental factors, lifestyle factors, but often errors in cell division during spermatogenesis. This results in sperm having shrunken, enlarged, multiple, or even no heads. In some instances, sperm can have multiple tails which would suggest that they are more efficient swimmers, but both sperm with too many heads or tails have malformed genetic material that leads to miscarriages.
Immune Systems Think They’re the Enemy
Sperm are unique to other cells in order to swim to the egg, but because of the difference, it can be mistaken as a foreign invader by the female immune system. Their immune systems react by releasing antibodies to fight against sperm, but specialized cells produced in the testicles act as bodyguards, making them a hype man away from a successful entourage.
Human Sperm Is Not as Cooperative as Other Species
Human sperm is known for being competitive, rat and mice sperm appear to be more cooperative. Shaped slighting different with hooked heads resembling talons, a 2007 study found that their shape allowed them to hook on to other sperm and form trains, in order to ensure meeting the egg more efficiently. Study authors suspect that instead of competing against each other, sperm from a single host cooperate to compete against the sperm of other males. There’s no evidence that adorable conga lines apply to people, but human sperm could learn a lot from rodents about working together. Sadly, their little dense heads don’t have the capacity for that.
Sperm Never Go Away
Unlike female eggs, sperm are constantly regenerated every 42 to 76 days, studies show. The renewal system allows for men to potentially improve sperm quality through lifestyle changes, but the catch is that men have to orgasm regularly as well in order to benefit. Sperm that stay in the testes too long are more likely to mutate. The good news and bad news is that sperm won’t stop regenerating until you die. Although male fertility declines with age, men still need a release to stay healthy—another great reason to keep the romance alive after having children — if that’s possible.