It is a commonly held belief. The sperm cells are like epic race runners, competing against each other to access the coveted eggs at the finish line. The egg patiently waits for victory sperm to stab its outer membrane, causing fertilization. This story of lace sperm and waiting eggs lasted over time, but still not accurate. Scientific research has exposed this idea over and over again.
In her new book, The Stronger Sex: What Science Talks About the Power of the Female Body (Seal Press/Hachette, 2025), science writer Star Vartan addresses this and other widespread myths about the female body, highlighting that science actually speaks of gender differences, and that knowledge gaps still exist, historical research exists.
Eggs are selective (but we keep forgetting)
Mammal adaptation to make all eggs at once, stress-test and dump most of them, and have something available at once for fertilization. It represents a change in reproductive strategy, according to Professor Linnet Siebert, a biologist at the University of Massachusetts at Amherst. That shift away from the earlier or older breeding methods that fish, amphibians, and most reptiles still have great success today.
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They both make both eggs and sperm continuously, in large quantities, and throughout their lifetime until they die. Female fish and frogs drive egg masses out into the water, while males shoot and deposit sperm in the direction of the egg, or generally aim. Fertilized eggs develop due to environmental conditions – or do not, or are eaten by predators. Sea turtles have sex, but they still lay hundreds of fertilized eggs at a time, and do so until they are older, as do egg-laden snakes (biofat snakes live younger).
For all these animals, Reproduction is a number game. There are plenty of eggs, lots of sperm, lots of fertilizer and lots of hatched eggs, with only a few young people surviving into adulthood. In many cases, newly hatched turtles, tadpoles and weesnake byeby are important food sources for other animals living in ecosystems, like biological offerings to larger communities.
This more fertile, robust design is still adopted by male humans, but not female.
Related: Does sperm really compete for eggs?
“Human men still follow the fish pattern. They still produce a million sperm. They don’t clean up the sperm, they don’t produce the best sperm, they just put out all the sperm like fish,” says Siebert. She wonders why female mammals have made a major transition from that model. “Why were male sperm and mammals never chosen to be egg-like? Something changed and that separated the gender,” she says. This is an unanswered biological question, but there is one obvious possible answer: control.
Female mammals house the mechanisms in which eggs (and sperm) are used to breed within the body, while amphibians, reptiles and fish exclude ecological conditions such as temperature, predators, salinity and pollutants. Both strategies are clearly effective, but why did mammals move from successful models?
Long-lived mammals may be able to store epigenetic information about their local state as they grow. Choices about who lives and who is not made will instead bring the best offspring to the current conditions instead.
Why is this problem all this problem in Bohannon the cat “turning your body into an eggshell” in her book “Eve: How a woman’s body pushed for 200 million years of evolution?” This can be explained by the combination of energy and fine tuning. By bringing fertilization and growing young within a female body, mammals can use living experiences (as well as the moment of conception) to influence which traits are chosen. They can do this by controlling both which eggs and which sperm is preferred.
All this energy used in the stage of conception or before it means that there are fewer fertilized eggs and fewer babies. If you only have one or two babies at a time, instead of hundreds, it will be logical to invest in ensuring that it has the best chance of survival. Therefore, the female body of choice about egg fights and sperm makes perfect sense. This is the case with the following year of raising children.
The selection of sperm by eggs is a fundamental biological fact that has been “discovered” many times over the years. Despite the facts, the stubbornness of the “active sperm and waiting egg” story highlights how difficult it is for humans to accept biological stories that go against our cultural ideas.
As Emily Martin detailed in his memorable paper, we know that the story was once a sperm was an active party of fertilization, and that the swift, harsh sperm was trying to be the first to swim at each other, attacking the outer membrane of the eggs and depositing DNA packages.
Back in the mid-1980s, it was first discovered that eggs were in fact active decision-makers of fertilization. The egg uses Zona Pellucida (a thick protein coat that protects egg cells) to chemically grab the sperm, test it, and reject or admit that DNA to the egg. Reciprocating sperm cannot be broken even by a single chemical bond, but eggs can. Research in the 1990s went to support that idea, and it has become widely accepted.
However, for the past 20 years, scientists have continued to “discover” this fact. In 2017, Quanta Magazine published an article about researchers who “challenge this doctrine” that they are not the obedient traditional cells that scientists have long thought of. And an article in the University of Virginia magazine states: It promotes the fusion of the two. The author called this an “unexpected discovery.”
This “rediscovery” of already known scientific information about the interaction of eggs and sperm was covered in a 2024 article in Ms. Magazine about Evelyn Fox Keller, a pioneer in the field of feminist philosophy of science. The idea of passive eggs/active sperm just doesn’t go away, even in the same journal that published a study that said it wasn’t true. “One of Fox Keller’s key findings was that seemingly neutral assumptions in biology can actually be gendered. Researchers and Science Press show that they have been making the same “discovery” for decades.
Latest evidence shows that not only determine which sperm the egg wants to recognize, it can attract or repel different sperm even before the egg reaches the egg.
In 2020, scientists from Stockholm University, working with colleagues at the University of Manchester, discovered that eggs release chemicals that can attract sperm when they travel. They also discovered that different eggs attract different types of sperm – not all eggs attract the same sperm. Eggs sometimes attracted sperm that was not their partner’s.
They understood this by obtaining reproductive materials from a couple who gave permission at an IVF clinic in Manchester, UK. “Each experimental block constituted follicular fluid and sperm samples from a unique set of two couples, and each male sperm was exposed to follicular fluid from their partner and non-pastor.
Chemosensory communication between eggs and sperm allows for “female choice and fertilizer fertilizer for specific men,” the researchers write. What is the standard for eggs? It’s unknown at this point. It is possible that in some way you will choose a high-quality sperm or sperm that is more genetically compatible. “This shows that human egg-sperm interactions depend on the specific identities of women and men involved,” one researcher told Labroots. He went on to say that the sperm choice had completely reached the egg.
Science shows that, contrary to some cultural narratives, the menstrual cycle is extremely sensitive to energy savings. Eggs go to war every month, ensuring only the strongest ones survive. That winner’s egg will signal it to the sperm it likes. And it selects sperm to unite to create a possible new human.
Due to the inherent weaknesses of the female body and the passive female reproductive system.
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