Why are there as many males as females?

Why are some people left-handed?

About one-tenth of the world’s population are left-handed. Why does the trait exist in the first place? This five-minute video investigates how the uneven ratio of lefties and righties gives insight into a balance between competitive and cooperative pressures on human evolution.

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.

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

Girls are born with an estimated 1 million to 2 million eggs in their bodies, but around 10,000 die monthly before puberty. Scientists have not yet figured out why there's such an excessive number of eggs prior to menstruation, but they've calculated that there are roughly 300,000 to 400,000 eggs left at puberty.

Men and women didn't evolve to perform segregated hunter-gatherer duties

The often-cited theory that men evolved to hunt and women evolved to gather is wrong. This article explores the origins of the "Man the Hunter" theory and the mounting evidence that undermines it. Exercise science indicates that those assigned...

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.

The science of symmetry | The Royal Society

Nature is full of symmetries, from spiral galaxies to florets of broccoli. So why do complex creatures break the pattern?This short video discusses why symmetry came to dominate life on Earth, and how many complex life forms, such as humans, transitioned from radial to lateral symmetry.

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.

Women's health research continues to be underfunded

Health conditions that affect women more than men get less research funding. This interactive collection of graphs details the gendered gap in health research funding. Of the conditions that affect one sex more than another, those that create the...

Why genetic similarities between humans suggest a past near-extinction event

Researchers have found that low genetic diversity among humans—even those on opposite sides of the planet—may result from a breeding population of as few as 1,280 adults, estimated to have existed 930,000 years ago. This genetic bottleneck may have resulted from a near-extinction or from a small population of human ancestors, from which we all descend, that broke off from a larger population.

Why physiology and genetics prevent king bees from existing

The mating process is fatal to male honey bees, as their endophallus detaches from their bodies and remains temporarily within the queen. Because fertilized honey bee eggs develop into female bees, if a male somehow did survive and become king, his line of succession would also abruptly end.

Half of human DNA is inherited from each parent

Within most cells reside 23 pairs of chromosomes made of tightly wound DNA, and half of each pair is inherited from each parent. The 23rd pair consists of two X-shaped chromosomes, or one such chromosome paired with a Y chromosome, and determines biological sex.

Genetics may account for nearly 67% of mosquito attractiveness

In a mosquito attraction study published in 2015, identical twins appeared equally attractive to mosquitoes in lab tests, whereas some nonidentical twins were far less likely to be bitten than their siblings. Other work related showed that body odor is also more similar between identical twins.

View a breakdown of the identified species on Earth

Over 2 million species have been documented by scientists, but there may be as many as a billion distinct species. The vast majority of the species on Earth are insects, while mammals form the smallest group.

Energy from the Big Bang should have created equal amounts of matter and antimatter

Compared to antimatter, the abundance of normal matter suggests the symmetry between the two broke down at some point in the early universe. Research is ongoing to uncover a responsible mechanism, which would revise the Standard Model.

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.

Before Title IX, boys competing in high school sports far outnumbered girls

In 1971, the year before Title IX was passed, about 294,000 girls were playing high school sports. That paled in comparison to the number of boys: 3.7M.

Nobel Prizes in science have heavily favored male, North American, and European scientists

Most science laureates come from established academic institutions, and limited outreach and nomination rules have biased against researchers from low- and middle-income countries. As of 2024, China ranks among the world’s top scientific contributors, but has only won 10 Nobel Prizes in the sciences.

Distinguishing polar and nonpolar molecules and why charges get distributed unevenly in molecules

Because each element has a unique number of protons and configuration where electrons exist, they attract electrons that are shared with other elements in chemical bonds to varying degrees. When this attraction—electronegativity—varies between two bonded elements, electrons are more likely to be near the more electronegative element and away from the less electronegative element. This can create regions of opposite charge, or poles, and thus polar molecules.

An analysis of the logistic map, which shows how chaos can emerge from simple equations

When modeling systems such as the predator-prey cycle of an organism's population in an ecosystem, the logistic map function shows the population normally settles into an equilibrium value. However, at high reproduction and starvation rates, multiple such values arise, making it difficult to accurately model long-term population growth in some environments.

Testosterone prescriptions remain very low overall

Though demand for an injectable formulation of testosterone roughly doubled between 2019 and 2025, testosterone prescriptions still remain very uncommon—adding up to less than 2 per 100,000 prescriptions in 2025.

T. rex needed the same amount of calories as 80 people every day

Tyrannosaurus rex is the most extensively studied fossil creature ever known. Every year, new research is added to the towering list of papers that try to draw …

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

The US had roughly 1.6 million minimum wage workers as of 2021

Typically, minimum wage workers are young. They’re not only more likely to be a woman than a man, but also more likely to be single than married.

Jobs that marry each other the most

Out of all married physicians, roughly one in five is married to another physician. The trend extends beyond the medical field. Some professionals are more likely to marry one another than others. Find out which jobs most often pair together among married couples with this interactive tool based on estimates from the American Community Survey. Click here to type in your profession and see your most likely match.

Butterfly populations have declined by 22% from 2000 to 2020

Research suggests that one in every five butterflies is lost due to pesticide use, habitat loss, and climate change. Playing a vital role in pollination, their declining populations threaten plant reproduction and the health of ecosystems.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

Bone marrow generates roughly 500 billion new blood cells each day

Some of our bones are stuffed to the brim with a fatty, jam-like substance called marrow. Bone marrow comes in yellow and red, with the latter responsible for producing new blood cells, and has become critical in treating diseases like leukemia.

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

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

See how each of the more than two million known species relates to each other—and to common ancestors—in this zoomable tree of 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.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.

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.

Coral reefs get their colors from zooxanthellae—microorganisms that line corals' digestive tracts and provide them with sugars in exchange for a home within this protective tissue.

Learn how your body is, scientifically, like a firework with its own slow, controlled burn.

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.

The US dollar is the most widely circulated currency in the world, and is involved in nearly 90% of global transactions

Despite being favored by 87% of Americans, Congress does not have term limits.

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

US housing costs have risen by roughly 175% between 1991 and 2026—but a growing number of Gen Zers are becoming homeowners anyway. In 2025, 4% of homebuyers were Gen Z, up from 3% the year before.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

Electrical grids worldwide must double their power delivery capacity by 2050 to meet surging demand from AI and electric vehicles.

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.

Browse a detailed visual analysis of over 200,000 similes—comparisons that often use 'like' or 'as'—from popular fiction to see how frequently writers the same idiomatic expressions.

Hedge funds, the private investment firms that trade a wide swath of financial assets, make money by imposing steep fees on investors and from the fund's investment performance.

In 2026, Finland was named the world's happiest country for the ninth consecutive year based on its wealth, social safety network, and high life expectancy, among other factors.

Budweiser stores yeast derived from the original 1800s strain in a secret bunker, which only the Head of Yeast Management can access—not even the CEO

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

44% of Americans say they pray at least once a day—discover how your state's religiosity stacks up against the rest of the country.