Chronological versus biological age

Aging is a complex biological process affecting our cells, tissues, and organs

With each passing decade, researchers uncover additional causes and effects of this seemingly unstoppable process. This visually stimulating video dives into our current understanding of aging, complete with the biological hallmarks researchers use to study aging at the cellular level (biological age).

Epigenetic clock: DNA alterations on cells that predict biological age

Epigenetics refers to a biological process that controls whether certain genes are expressed or not. With a rising interest in the concept of biological age, researchers have discovered a cellular change known as DNA methylation that leaves a fingerprint on our genome as we age.

Biological aging tests assess the breakdown of physiological systems

Known as aging clocks, these tests compare various metrics, like DNA methylation patterns and protein profiles, to healthy baselines. However, the non-uniformity of these baselines across individuals limits testing accuracy and prevents their clinical use.

Doctors use three key physical markers to determine biological aging

The length of the ends of chromosomes (known as "telomeres"), the gradual change in collections of DNA molecules called "methyl groups", and the secretion of inflammatory proteins are all used as indicators of biological age.

Can humans delay or reverse old age?

We're not sure yet. Researchers at the University of California San Francisco are studying why some conditions and behaviors, such as low-oxygen environments and exercise, benefit the aging process, hoping to reveal potential health applications. Some of this research focuses on klotho, a naturally occurring age-regulating hormone named after the Greek Fate Clotho. Animal studies on klotho brain injections found subjects had improved memory recall and age-related degeneration resistance.

Do people really look younger than they used to?

Why do people today look younger than they used to? From style to science, there are 3 surprising reasons we age differently now.

Your brain appears to age in five distinct stages

Analysis of brain scans from about 4,000 people has helped scientists identify five major stages of our brain's maturation from birth to death. The pattern of connections inside our brains seem to shift, on average, at ages 9, 32, 66 and 83. (Some readers may experience a paywall.)

Perceived isolation ages you

Mounting evidence suggests that socialization is a vital component of maintaining good health. Research published in 2024 from Mayo Clinic researchers analyzed the social lives of more than 280,000 adults and concluded that individuals that weren't likely to participate in extracurricular social activities and get-togethers were more likely to have a biological age older than their actual age—meaning that you may be 60 but health indicators would suggest you're older.

Super-agers: seniors 80 and above with the memory ability of people in their 50s

Studies show the number one indicator of whether someone is a "super-ager" is not diet or genetics, but the extent of their social relationships. Moreover, scans reveal noticeable physical differences in certain parts of the brain in patients with extensive social networks.

Health span: The number of years one is active and disease-free

As scientific advances continue to extend the average human lifespan, many are now turning their attention toward extending "health span." The ultimate goal would be to extend one's health span to match one's lifespan, which would necessitate a shift in focus toward the pursuit of healthy aging. (Some users may experience a paywall.)

Why do humans have such long childhoods?

Humans have over twice as long childhoods than other animals with similar lifespans like whales and elephants. A human child can grow for nearly 20 years before they become a reproducing adult. Researchers believe there's a connection between long childhoods and human's unusually large brain size, though the science is not totally clear. Dive into what scientists know here.

Circadian rhythms shift as we age—making older adults want to go to bed earlier

Throughout our lives our internal biological clocks shift. Early-to-rise toddlers become hard-to-wake teens and eventually early-to-sleep seniors. Circadian rhythm fluctuations throughout our life cycle explain some of these changes.

Chronobiologists study the effect of time on biological cycles

Circadian rhythms were first observed in the 1700s, when French astronomer Jean-Jacques D'Ortous de Mairan put a plant in a dark room and watched it still respond to day and night cycles, setting off further studies about specific light-dark biological cycles, an area of inquiry that continues today with the human "clock proteins" at the molecular level.

Paleontologists apply rules about rock layering, fossilization, and radioactivity to date geological samples

Concepts such as the understanding that older rock layers will form beneath newer ones allow scientists to compare the ages of samples from various layers. Although no geological site preserves evidence across all time, samples can be combined with fossils of known age, such as those dated by analyzing the decay of their radioactive isotopes, to reconstruct Earth's timeline.

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.

Time dilation explains that movement through space affects the passage of time

According to special relativity, everything in the universe moves through space-time at the speed of light. Just as turning from north to northwest on a road reduces one's northward motion, moving through space leaves less of this speed to move through time, causing an object to age more slowly.

Calculate your Social Security full retirement age

The year you were born determines when you become eligible for your Social Security full retirement age benefit. Spoiler alert, that age is no longer always 65. If you want to use this calculator to determine your full retirement age—and learn more about the drawbacks of claiming Social Security early—click here.

Some data links schizophrenia to older paternal age and birth complications

Yet both associations are not yet considered firm enough to definitively be causative. Schizophrenia is a multi-causal syndrome and a mixture of factors, including genetics, are widely believed to be behind its development.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

1440: Everything you need to know about Alzheimer's

What is Alzheimer's, and is it different from dementia? In short, yes—Alzheimer's is a specific brain disease that falls under the umbrella of dementia. However it is the most prevalent form of the condition, accounting for 60 to 80% of reported dementia cases.

Meteorological v. astronomical seasons, explained

Meteorologists and climatologists define seasons differently from “regular” or astronomical spring, summer, fall, and winter. Traditional seasons reflect the movement of celestial objects, known as the astronomical seasons; meteorologists mark seasonal change based on temperature averages.

Mineral and chemical sunscreens protect differently but both guard against UV damage

UVA rays age the skin, while UVB rays are more directly linked to skin cancer. Mineral sunscreens, with ingredients like zinc oxide, physically block rays, while chemical ones absorb UV and turn it into heat.

An interactive look at your own life through demographics

This interactive site allows you to understand the journey of your life in numbers and dates. World Data Lab asks users to enter their date of birth, country of birth, and sex at birth. The site then provides an interactive page tailored to your...

How do you sequence a genome?

If the genome is made up of microscopic chromosomes, how do scientists actually sequence it? Here's a 5-minute video explaining one of the most common processes.

When is someone actually dead?

Death is a process, not a sudden flip of a switch. Technology can now interrupt this process at various stages, begging the question of when exactly death happens in the dying process. This 33-minute podcast episode explores this question and the...

If aliens visited Earth, it seems unlikely they'd be evolved biological creatures like us

The writer behind Mindless Algorithm, George McGowan, challenges various assumptions about aliens depicted in science fiction. One of those is that aliens are, like humans, individual entities that live, age, and die. McGowan suggests that the difficulty of intergalactic travel and the aliens' technological advancements make it more likely that they'd be an advanced form of AI or digital copies of biological entities.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

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

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

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

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

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

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

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.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

Crows are believed to have intelligence on par with a seven-year-old child and demonstrate complex behaviors, from problem-solving with tools to recognizing human faces.

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.

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.

At the beginning of the 20th century, a group of young men ate standard American food—replete with food additives like borax and formaldehyde—as part of government research to better understand food safety.

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.

According to the physics of black holes, our 4D reality may be a hologram—a projection of information coded on a 2D surface on the edge of the universe.

A century of Billboard issues documenting the evolution of popular music.

Salvador Dalí believed he was his own dead brother, who had died nine months before he was born

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

The term 'algorithm' originated from the Latinized name of al-Khwārizmī, a 9th-century mathematician whose works introduced Arabic numerals and the decimal-based numeral system to Europe and whose treatise 'Al-Jabr' gave algebra its name.

See how Ebola tore through Guinea, Sierra Leone, and Liberia in 2014-2016.

The US Constitution is widely regarded as the longest-standing written national constitution still in force—see how it has influenced rights worldwide.

The first steps to rebuilding your credit score include getting to know exactly what's on your credit report and figuring out how far you are from the '700 club,' or 'good score' range.

Warren Buffett's former professor Benjamin Graham is known as the 'father of value investing,' a strategy in which investors seek to buy stocks trading below their intrinsic worth.