Women are born with all the eggs they will ever produce in their lifetime

The number and quality of sperm in men's semen is down, giving rise to various movements to avoid 'spermpocalypse'

A typical fertile, healthy young man produces over 100 million spermatozoa, or sperm cells, in his testicles every day. Scientists agree sperm figures are generally moving in the wrong direction, but also emphasize there's still a lot to learn about sperm.

Menstruation, which occurs monthly, is the release of an unfertilized egg

This routine vaginal bleeding is part of a woman's hormonal cycle and occurs after an egg is released by an ovary during ovulation and isn't fertilized. Also known as periods, this monthly occurrence can cause symptoms including cramping, fatigue, and mood changes.

Girls are hitting puberty earlier than ever before

Around the world, there has been a spike in children—especially girls—experiencing early puberty and doctors are seeking to understand why. The rise has been particularly strong post-2020. Early-maturing girls are at a higher risk for developing...

Why are there as many males as females?

Pretty much every species breaks down with an equal sex-ratio, with roughly the same number of males as females. But on the surface, it appears that most species wouldn't need many males to keep the population growing, with their energy-efficient, abundant sex cell production. So why is it equal? Scientists argue an equal ratio is the most evolutionarily stable. Learn about this quirk of biology here.

Some female tardigrades reabsorb their eggs if no male fertilizes them

The eggs are laid in skin that has detached after molting. These species undergo sexual reproduction, but others reproduce asexually, with females producing clones from unfertilized eggs. Some hermaphrodite species have both male and female reproductive organs and can self-fertilize.

As of 2022, scientists estimate that 117 billion people have been born on Earth

Although no demographic data exist for more than 99% of the time humans have existed, this value can be estimated by tracking approximate population sizes over different periods and the birth rates within those periods. In 2022, about 6.8% of humans that have ever been born were alive.

Why are women more likely to suffer autoimmune diseases than men?

A majority of Americans with autoimmune diseases have more than one X chromosome, a typical marker of the female biological sex, according to a study published in February of 2024. During fetal development, cells side with one X chromosome over the other, preventing the overproduction of X-chromosome-specific proteins and shutting down the twin chromosome. This article explores how this X-chromosome inactivation can lead to autoimmune disorders by generating antibodies to the body's own tissues.

Scientists have not yet answered what the evolutionary benefit may be of menopause

Few animals are known to experience menopause, raising questions about why it would be evolutionarily advantageous to have women survive past their reproductive years. One leading hypothesis is the grandmother hypothesis—older women and other species known to experience menopause, like whales, can aid families and pass down knowledge to future generations.

Cells create more organelles and duplicate their genetic material before dividing

As part of the cell cycle, this ensures that after mitosis—the process of cell division—the two resulting daughter cells possess the tools necessary to complete the functions of their parent cell, including accumulating energy and making proteins. During meiosis, four egg or sperm cells are created, each with half the parent cell's DNA.

How women grow tiny humans inside of them

Pregnancy is a complex biological journey, lasting about 40 weeks. When a sperm fertilizes an egg, that event triggers intricate cellular and hormonal processes, driven by hardwired cellular instructions, which lead to cell division, differentiation, and development—ultimately culminating in the birth of a baby.

The history of ectogenesis and artificial wombs

While the science of artificial wombs is new, the idea goes back to a 1923 Heretics Society of the University of Cambridge lecture where an English biologist was one of the first people to propose an egg could be fertilized outside the womb. This...

Bone marrow (soft tissue found inside certain bones) generates roughly 500 billion new blood cells each day

Kids often grow out of allergies to milk and eggs

Between 60% and 80% of kids with allergies to milk or eggs outgrow them by age 16. The immune system doesn’t always recognize and respond to baked forms of these allergens, so when kids eat muffins and other cooked food products, their immune system may become more habituated to them and overcome food sensitivities. Aging out of other allergies is less common.

Cells can last in the human body from days to a person's entire life

Despite claims that a person's body replaces itself every seven to 10 years, the rate at which cells die and are replaced varies by cell type. Gastrointestinal cells that line the digestive tract and stomach last only a few days, while some heart muscle cells and most neurons are around from birth until death.

Estrogen is a really important hormone for men, too

Many people may be familiar with the idea that too much estrogen can cause infertility and other complications, including erectile dysfunction, but too little estrogen is also a significant medical concern because it can result in a reduced sex drive and limit overall growth.

The story of the most prolific mother ever

An 18th-century Russian woman gave birth to 69 children through 27 pregnancies, with an unbelievable 16 pairs of twins, seven triplets, and four quadruplets.

Ordinary bee larvae can develop into queen bees upon being fed royal jelly

Royal jelly is a protein-rich, yellowish substance produced by worker bees in a honeybee hive. After three days, only a few continue receiving the jelly, which triggers the development of ovaries and other traits not found in workers. The first candidate to emerge becomes queen.

South Korea has the lowest fertility rate in the world

If current birthing trends persist, every hundred South Koreans today will have only six great-grandchildren between them. This crisis is a result of high expenses, harsh work-family trade-offs for women, declining marriage rates, and other societal factors. Some newer policies are helping to build incentives for having children, but larger issues also need to be addressed.

What causes high cholesterol?

Cholesterol is a complex health issue, and for a long time, the American Health Association recommended Americans not eat more than three eggs a week to avoid it. But scientific advancements on the impact of different types of cholesterol revealed eggs aren't so bad. So what is it, and how does it effect us? Dive into the digestive tract here.

Each day, about 60 US pregnancies end in stillbirth

This online memorial for families who experienced the unexpected death of a fetus 20 weeks or older is the result of ProPublica reporters inviting 60 families to share their baby's name and answer some questions about their unfulfilled wishes for their children. About 21,000 babies are stillborn in the US annually. About the same number of children die in the US during their first year of life.

What happens to golf balls after they're used?

With over 1 billion golf balls produced annually, an estimated 300 million to 1.5 billion are lost worldwide. On average, thousands of balls are left behind on each course, often ending up in ponds, forests, and beaches. While many golf courses recover and reuse some of these balls, studies suggest countless remain unretrieved.

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

Ticks survived 27 years in a lab, including eight without food

Research published in 2022 set a new record for tick longevity. A group of adult African ticks that are normally found in eastern and southern Africa lived in a laboratory for 27 years, including eight without food. What's more, one of the females laid eggs at least four years after the last male died. Most ticks, on average, reportedly live for six months to three years.

Eggshell color doesn't indicate taste or superiority

Brown, white, and blue eggs taste and cook identically. Despite popular notions that brown eggs are superior, the shell color reflects the genetics of the hen alone. What actually determines egg quality is freshness and the diet of the hen (where grass and leafy greens lead to denser yolks). And freshness can go both ways: older eggs peel more easily than fresh ones.

Billions of flies are being dropped from the sky

The US is dropping billions of sterile flies to stop a deadly parasite. Screwworm maggots eat animals alive, so scientists are collapsing the population by ensuring females can’t reproduce.

Each taste bud has 10 to 50 sensory cells that form a flower-like capsule

At the top of the structure are thin filaments known as "taste hairs" that bind taste-producing substances to the surfaces of the cell, after which corresponding electrical signals are sent to the brain. Adults have 2,000 to 4,000 taste buds on their tongue.

The odds of a perfect March Madness bracket are worse than finding one specific grain of sand on Earth

With 63 games to predict, random guessing produces odds of 1 in 9.2 quintillion. Even an informed picker who gets 67% of games right faces odds of about 1 in 120 billion, meaning if every American filled out a unique bracket, we'd expect a perfect one in roughly 366 years.

Indefinite cloning of some endangered species may not sustain their longevity because cloning success rates decrease as genetic mutations accumulate.

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.

About 2,000 US babies are born annually without some portion of their limbs, potentially leading to a lifetime of pricey prosthetics.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

Up to a million Girl Scouts sell about 200 million cookie boxes every spring, generating $800 million, largely because refusing a child is frowned upon

Use this calculator to find the dollar value of your mental load, from meal planning to coordinating after-school care for your children.

Researchers believe the brain consolidates memories, processes emotions, and plans for the future during dream states

Children are now three times more likely to say they want to be a YouTuber when they grow up than an astronaut, with some even attending 'YouTube camps' that teach kids how to create content for the platform.

Apeirophobia is an overwhelming fear of living forever, perhaps stemming from the brain's inability to conceptualize an infinite life.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

American short story writer Flannery O'Connor raised 40 peacocks, which became potent symbols for her fiction's elegant violence

English mathematician Ada Lovelace wrote the first computer algorithm a century before computers existed and hypothesized that computing devices would one day be able to compose music—foreseeing the generative AI systems of today.

11 people died from firework injuries in the US in 2024.

20,000 letters to the advice columnist 'Dear Abby' provide insight into prevailing sex, religion, and LGBTQ fears, anxieties, and concerns from the 1950s onward.

Visualize the path of every solar eclipse from 1900 to 2099 and see what each looks like when observed from different locations on Earth.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

Scientists have struggled to pin down Ebola's natural reservoir species for decades, but the available evidence suggests that it's very likely fruit and insect-eating bats found in Africa.

As of 2025, the most cited papers in science include a review of graphene, methods to improve image recognition, streamlining electron density calculations, and optimizing protein studies.

While the first exchange-traded fund (a 'basket' of different assets that can be bought and sold on a stock exchange) in the US only launched in 1993, the global ETF market has grown to more than $10T in the short time since.

In 1963, a basement renovation in Turkey revealed a passageway to a hidden, multilevel underground city that once housed as many as 20,000 people

Apollo astronauts left items in the moon's 'toss zone,' including golf balls, family photos, and bags of human waste, to make room for lunar rocks.

Brandi Chastain, the star of the 1999 US victory over China in the 1999 Women's World Cup, was a last-second choice to take the penalty kick that sealed the victory.

The boiling temperature of water decreases with increasing elevation because the molecules need less energy to overcome the lower atmospheric pressure associated with thinner air.