Sperm Warfare (Or: Why it Takes 1 Billion Sperm to Make One Zygote)

iStock/Bet_Noire
iStock/Bet_Noire

The average man produces roughly 525 billion sperm cells over his lifetime and releases, in one way or another, more than one billion of them per month and anywhere from 40 million to 1.2 billion in a single ejaculation. The males of other species boast some equally impressive numbers: 280 million, 1 billion and 3 billion per ejaculate for rabbits, sheep and bulls, respectively. If it only takes one sperm cell to fertilize an egg, though, why produce so many?

The Seminal Wars

The females of many species mate with and receive the sperm of multiple males, often in quick succession. Deep in the lady’s nether regions, those sperm compete to fertilize the egg. Now, if you’re serious about winning a lottery or a raffle, you don’t buy just one ticket do you? No, you buy several to increase your probability of winning. Sperm, in a way, are a lot like lottery tickets. If you’re serious about passing on your genes, then you want to get as many sperm as possible near a fertile egg cell. (In other ways, they’re not like lottery tickets at all, and I would discourage you from trying to buy them in gas stations or convenience stores.) For a male, the more of his sperm going up against his rivals’ seed, the merrier.

Sperm competition is such a powerful selective pressure, in fact, that it influences the size of the testes and the volume of ejaculate of some animals and causes others to modulate the amount of sperm they produce based on the presence of a rival male. Male chimpanzees, who face high levels of sperm competition, possess the largest testes among the great apes. Gorillas, who face almost no sperm competition thanks to a rigid social structure where the dominant male alone gets to mate with all the females, don’t need to waste precious energy and resources on sperm production and hence have some downright dinky testes—almost 15 times smaller than chimps’ (relative to their body weight).

Male humans would feel somewhat embarrassed if they were naked in a locker room full of chimps, but still pretty good about themselves if they were naked and surrounded by silverbacks (nervous, too, perhaps). Evolutionary biologists are still trying to work out whether our relatively large testes are leftovers from some point in our evolutionary past, or if sperm competition was at one point an important factor in human reproduction.

It’s not a sprint. It’s a marathon

Sperm competition isn’t a prevalent problem among modern Homo sapiens and guys don’t really need a veritable army of sperm to race someone else’s genes to an egg. We still need an awful lot of those squiggly little cells, though, because even if there’s no other sperm to compete against, every man’s little swimmers still have to fight in a battle of the sexes. Females demand only the finest sperm for their eggs, and the war their bodies wage on sperm is one of attrition.

After insemination, the sperm cells of humans, and many other species, have a long trip ahead of them, relative to their tiny size. At every step of the way, many sperm cells run out of energy or die and their surviving brothers are forced to leave them behind: only a portion of the sperm that are deposited into the vagina make it to the uterus, an even smaller group get to the oviducts and a fraction of those make their way to the upper oviduct where the egg is actually located. Once the sperm reach the egg, things don’t get any easier. One does not simply walk into Mordor. The egg is covered by a thick layer of gelatinous, follicular cells called the cumulus oophorus, which acts as a barrier, and it often takes the assault of several sperm cells to break it down enough for one lucky one to get through and fertilize the egg. Charles Lindemann, who researches the mechanisms of sperm motility at Oakland University in Rochester, Michigan, likens the whole ordeal to a “marathon run in a maze filled with mucus followed by an obstacle course.”

The odds stacked against any single sperm cell making the grueling journey to the egg can be offset by producing a large number of sperm. While just a small fraction of the sperm will reach their destination and do the job they were made to do, having a few million more cells backing them up makes for a pretty good reproductive insurance policy.

Save Up to 80 Percent on Furniture, Home Decor, and Appliances During Wayfair's Way Day 2020 Sale

Wayfair
Wayfair

From September 23 to September 24, customers can get as much as 80 percent off home decor, furniture, WFH essentials, kitchen appliances, and more during the Wayfair's Way Day 2020 sale. Additionally, when you buy a select Samsung appliance during the sale, you'll also get a $200 Wayfair gift card once the product ships. Make sure to see all that the Way Day 2020 sale has to offer. These prices won’t last long, so we've also compiled a list of the best deals for your home below.

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15 Mysterious Facts About Agatha Christie

British mystery author Agatha Christie autographing French editions of her books in 1950.
British mystery author Agatha Christie autographing French editions of her books in 1950.
Hulton Archive/Getty Images

With over 2 billion copies of her books in print, British novelist Agatha Christie (1890-1976) has kept countless readers up into the early morning hours. Occasionally, the mystery surrounding her personal life—including a high-profile disappearance in the 1920s—has rivaled the best of her fiction. Let's take a look at some of the verifiable details of the famed crime writer’s life and times.

1. Agatha Christie's mother was against her daughter learning to read.

Before becoming a bestselling novelist, Agatha Christie was in real danger of growing up an illiterate. Her mother was said to be against her daughter learning how to read until age 8 (Christie taught herself) and insisted on home-schooling the budding author. Mrs. Christie refused to let Agatha pursue any formal education until the age of 15, when her family dispatched her to a Paris finishing school.

2. Agatha Christie's first novel was written on a dare.

After an adolescence spent reading books and writing stories, Christie’s sister Madge dared her sibling to attack a novel-length project. Christie accepted the challenge and penned The Mysterious Affair at Styles, a mystery featuring a soldier on sick leave who finds himself embroiled in a poisoning at a friend’s estate. The novel, which featured Hercule Poirot, was rejected by six publishers before being printed in 1920.

3. Hercule Poirot was based on a real person.

The dapper Poirot, a mustachioed detective who took a gentleman's approach to crime-solving, might be Christie’s best-known creation. Christie was said to have been inspired when she caught sight of a Belgian man deboarding a bus in the early 1910s. He was reportedly a bit odd-looking, with a curious style of facial hair and a quizzical expression. His fictional counterpart's debut in The Mysterious Affair at Styles would be Poirot's first of more than 40 appearances.

4. Agatha Christie once disappeared for 10 days.

Hulton Archive/Getty Images

In 1926, Christie—who was already garnering a large and loyal fan base—left her home in London without a trace. It could’ve been the beginning of one of her sordid stories, particularly since her husband, Archie, had recently disclosed he had fallen in love with another woman and wanted a divorce. A police manhunt ensued, although it was unnecessary: Christie had simply driven out of town to a spa, possibly to get her mind off her tumultuous home life. The author made no mention of it in her later autobiography; some speculated it was a publicity stunt, while others believed the family's claim that she had experienced some kind of amnesic event.

5. Agatha Christie wasn't big on violence in her work.

While a murder is typically needed to set a murder mystery in motion, Christie’s preferred methodology for slaying her characters was poison: She had worked in a dispensary during wartime and had an intimate knowledge of pharmaceuticals. Rarely did her protagonists carry a gun; her two most famous detectives, Miss Marple and Hercule Poirot, were virtual pacifists.

6. Agatha Christie had an alias.

Not all of Christie’s work had a mortality rate. Beginning in 1930 and continuing through 1956, she wrote six romance novels under the pen name Mary Westmacott. The pseudonym was a construct of her middle name, Mary, with Westmacott being the surname of her relatives.

7. Agatha Christie loved surfing.

The image of Christie as a matronly author of mystery is the one most easily recognized by readers, but there was a time when Christie could be found catching waves. Along with her husband, Archie, Christie went on a traveling spree in 1922, starting in South Africa and winding up in Honolulu. At each step, the couple got progressively more capable riding surfboards; some historians believe they may have even been the first British surfers to learn how to ride standing up.

8. Agatha Christie didn't like taking an author's photo.

AFP/Getty Images

Although not explicitly camera-shy—Christie took frequent photos while traveling—she appeared to dislike having her photo appear on the dust jackets of her novels and once insisted they be issued without a likeness attached. It’s likely Christie preferred not to be recognized in public.

9. Agatha Christie took an oath of detective writing.

Founded in 1928 by writer Anthony Berkeley, the London Detection Club, or Famous Detection Club, was a social assembly of the notable crime writers in England. Members “swore” (tongue mostly in cheek) to never keep vital clues from their readers and to never use entirely fictional poisons as a plot crutch. Christie was a member in good standing, and took on the role of honorary president in 1956 on one condition: She never wanted to give any speeches.

10. Agatha Christie tried her best to take up smoking.

While it would shortly gain a reputation for killing its devotees, smoking was once so revered that it seemed unusual not to take a puff. Shortly after the end of the first world war, Christie was quoted as saying she was disappointed she couldn’t seem to adopt the habit even though she had been trying.

11. Agatha Christie wrote a play that may never stop running.

The curtain was first raised on Mousetrap in London’s West End in 1952. More than 60 years later, it’s still being performed regularly and passed the 25,000 show mark in 2012. The play—about a group of people trapped in a snowbound cabin with a murderer among them—was originally a radio story, Three Blind Mice, that was written at the behest of Queen Mary in 1947.

12. Agatha Christie loved archaeology.

AFP/Getty Images

After divorcing alleged cad Archie, Christie married archaeologist Max Mallowan in 1930 and joined him for regular expeditions to Syria and Iraq. In 2015, HarperCollins published Come, Tell Me How You Live, the author’s long-forgotten 1946 memoir of her experiences traveling. Although she assisted her husband on digs, she never stopped working on her writing: Their preferred method of transport was frequently the Orient Express, a fact that likely inspired her Murder on the Orient Express.

13. At least one of Agatha Christie's fictional "victims" was inspired by a real-life nuisance.

When Mallowan married Christie, he was assistant to renowned archaeologist Sir Leonard Woolley. This fact upset Woolley’s wife, who refused to let Christie stay in a Mesopotamia digging camp; Mallowan was forced to take a train into Baghdad every night to see her. Christie soon wrote Murder in Mesopotamia: The victim was the wife of an archaeology field director who was bludgeoned with an antique mace. Christie dedicated the book to the Woolleys, who never joined Mallowan on an expedition again.

14. You can rent Agatha Christie's old home.

If you feel like inhabiting the same real estate as Christie is a bucket-list travel opportunity, her former home in Devonshire, England is available for rent. The centuries-old home was Christie’s summer getaway in the 1950s; portions of it are rented out to individuals or groups for $500 a night. Some furniture and a piano that once belonged to the author remain in residence.

15. The New York Times ran an obituary for Hercule Poirot when he "died."

Like Arthur Conan Doyle before her, Christie eventually grew tired of her trademark character and set about having Hercule Poirot perish in the 1975 novel Curtain. The reaction to his demise was so fierce that The New York Times published a front-page “obituary” for the character on August 6. Christie died the following year.

This story has been updated for 2020.