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Aging is complicated – a biologist explains why no two people or cells age the same way, and what this means for anti-aging interventions

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Aging is complicated – a biologist explains why no two people or cells age the same way, and what this means for anti-aging interventions

While some people may be older in chronological age, their biological age might be much younger.
FangXiaNuo/E+ via Getty Images

Ellen Quarles, University of Michigan

You likely know someone who seems to age slowly, appearing years younger than their birth date suggests. And you likely have seen the opposite – someone whose body and mind seem much more ravaged by time than others. Why do some people seem to glide though their golden years and others physiologically struggle in midlife?

I have worked in the field of aging for all of my scientific career, and I teach the cellular and molecular biology of aging at the University of Michigan. Aging research doesn’t tend to be about finding the one cure that fixes all that may ail you in old age. Instead, the last decade or two of work points to aging as a multi-factoral process – and no single intervention can stop it all.

What is aging?

There are many different definitions of aging, but scientists generally agree upon some common features: Aging is a time-dependent process that results in increased vulnerability to disease, injury and death. This process is both intrinsic, when your own body causes new problems, and extrinsic, when environmental insults damage your tissues.

Your body is comprised of trillions of cells, and each one is not only responsible for one or more functions specific to the tissue it resides in, but must also do all the work of keeping itself alive. This includes metabolizing nutrients, getting rid of waste, exchanging signals with other cells and adapting to stress.

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Aging results from a number of physiological factors.

The trouble is that every single process and component in each of your cells can be interrupted or damaged. So your cells spend a lot of energy each day preventing, recognizing and fixing those problems.

Aging can be thought of as a gradual loss of the ability to maintain homeostasis – a state of balance among body systems – either by not being able to prevent or recognize damage and poor function, or by not adequately or rapidly fixing problems as they occur. Aging results from a combination of these issues. Decades of research has shown that nearly every cellular process becomes more impaired with age.

Repairing DNA and recycling proteins

Most research on cellular aging focuses on studying how DNA and proteins change with age. Scientists are also beginning to address the potential roles many other important biomolecules in the cell play in aging as well.

One of the cell’s chief jobs is to maintain its DNA – the instruction manual a cell’s machinery reads to produce specific proteins. DNA maintenance involves protecting against, and accurately repairing, damage to genetic material and the molecules binding to it.

Proteins are the workers of the cell. They perform chemical reactions, provide structural support, send and receive messages, hold and release energy, and much more. If the protein is damaged, the cell uses mechanisms involving special proteins that either attempt to fix the broken protein or send it off for recycling. Similar mechanisms tuck proteins out of the way or destroy them when they are no longer needed. That way, its components can be used later to build a new protein.

Aging disrupts a delicate biological network

The cross-talk between the components inside cells, cells as a whole, organs and the environment is a complex and ever-changing network of information.

When all processes involved in creating and maintaining DNA and protein function are working normally, the different compartments within a cell serving specialized roles – called organelles – can maintain the cell’s health and function. For an organ to work well, the majority of the cells that make it up need to function well. And for a whole organism to survive and thrive, all of the organs in its body need to work well.

Illustration of cross-section of an animal cell and its organelles
Each organelle within a cell carries out specific functions.
Jian Fan/iStock via Getty Images Plus

Aging can lead to dysfunction at any of these levels, from the sub-cellular to the organismal. Maybe a gene encoding an important protein for DNA repair has become damaged, and now all of the other genes in the cell are more likely to be repaired incorrectly. Or perhaps the cell’s recycling systems are unable to degrade dysfunctional components anymore. Even the communication systems between cells, tissues and organs can become compromised, leaving the organism less able to respond to changes within the body.

Random chance can lead to a growing burden of molecular and cellular damage that is progressively less well-repaired over time. As this damage accumulates, the systems that are meant to fix it are accruing damage as well. This leads to a cycle of increasing wear and tear as cells age.

Anti-aging interventions

The interdependence of life’s cellular processes is a double-edged sword: Sufficiently damage one process, and all the other processes that interact with or depend on it become impaired. However, this interconnection also means that bolstering one highly interconnected process could improve related functions as well. In fact, this is how the most successful anti-aging interventions work.

There is no silver bullet to stop aging, but certain interventions do seem to slow aging in the laboratory. While there are ongoing clinical trials investigating different approaches in people, most existing data comes from animals like nematodes, flies, mice and nonhuman primates.

One of the best studied interventions is caloric restriction, which involves reducing the amount of calories an animal would normally eat without depriving them of necessary nutrients. An FDA-approved drug used in organ transplantation and some cancer treatments called rapamycin seems to work by using at least a subset of the same pathways that calorie restriction activates in the cell. Both affect signaling hubs that direct the cell to preserve the biomolecules it has rather than growing and building new biomolecules. Over time, this cellular version of “reduce, reuse, recycle” removes damaged components and leaves behind a higher proportion of functional components.

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The effects of calorie restriction on aging are still under study.

Other interventions include changing the levels of certain metabolites, selectively destroying senescent cells that have stopped dividing, changing the gut microbiome and behavioral modifications.

What all of these interventions have in common is that they affect core processes that are critical for cellular homeostasis, often become dysregulated or dysfunctional with age and are connected to other cellular maintenance systems. Often, these processes are the central drivers for mechanisms that protect DNA and proteins in the body.

There is no single cause of aging. No two people age the same way, and indeed, neither do any two cells. There are countless ways for your basic biology to go wrong over time, and these add up to create a unique network of aging-related factors for each person that make finding a one-size-fits-all anti-aging treatment extremely challenging.

However, researching interventions that target multiple important cellular processes simultaneously could help improve and maintain health for a greater portion of life. These advances could help people live longer lives in the process.The Conversation

Ellen Quarles, Assistant Professor in Molecular, Cellular, and Developmental Biology, University of Michigan

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Colors are objective, according to two philosophers − even though the blue you see doesn’t match what I see

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theconversation.com – Elay Shech, Professor of Philosophy, Auburn University – 2025-04-25 07:55:00

What appear to be blue and green spirals are actually the same color.
Akiyoshi Kitaoka

Elay Shech, Auburn University and Michael Watkins, Auburn University

Is your green my green? Probably not. What appears as pure green to me will likely look a bit yellowish or blueish to you. This is because visual systems vary from person to person. Moreover, an object’s color may appear differently against different backgrounds or under different lighting.

These facts might naturally lead you to think that colors are subjective. That, unlike features such as length and temperature, colors are not objective features. Either nothing has a true color, or colors are relative to observers and their viewing conditions.

But perceptual variation has misled you. We are philosophers who study colors, objectivity and science, and we argue in our book “The Metaphysics of Colors” that colors are as objective as length and temperature.

Perceptual variation

There is a surprising amount of variation in how people perceive the world. If you offer a group of people a spectrum of color chips ranging from chartreuse to purple and asked them to pick the unique green chip – the chip with no yellow or blue in it – their choices would vary considerably. Indeed, there wouldn’t be a single chip that most observers would agree is unique green.

Generally, an object’s background can result in dramatic changes in how you perceive its colors. If you place a gray object against a lighter background, it will appear darker than if you place it against a darker background. This variation in perception is perhaps most striking when viewing an object under different lighting, where a red apple could look green or blue.

Of course, that you experience something differently does not prove that what is experienced is not objective. Water that feels cold to one person may not feel cold to another. And although we do not know who is feeling the water “correctly,” or whether that question even makes sense, we can know the temperature of the water and presume that this temperature is independent of your experience.

Similarly, that you can change the appearance of something’s color is not the same as changing its color. You can make an apple look green or blue, but that is not evidence that the apple is not red.

Apple under a gradient of red to blue light
Under different lighting conditions, objects take on different colors.
Gyozo Vaczi/iStock via Getty Images Plus

For comparison, the Moon appears larger when it’s on the horizon than when it appears near its zenith. But the size of the Moon has not changed, only its appearance. Hence, that the appearance of an object’s color or size varies is, by itself, no reason to think that its color and size are not objective features of the object. In other words, the properties of an object are independent of how they appear to you.

That said, given that there is so much variation in how objects appear, how do you determine what color something actually is? Is there a way to determine the color of something despite the many different experiences you might have of it?

Matching colors

Perhaps determining the color of something is to determine whether it is red or blue. But we suggest a different approach. Notice that squares that appear to be the same shade of pink against different backgrounds look different against the same background.

Green, purple and orange squares with smaller squares in shades of pink placed at their centers and at the bottom of the image
The smaller squares may appear to be the same color, but if you compare them with the strip of squares at the bottom, they’re actually different shades.
Shobdohin/Wikimedia Commons, CC BY-SA

It’s easy to assume that to prove colors are objective would require knowing which observers, lighting conditions and backgrounds are the best, or “normal.” But determining the right observers and viewing conditions is not required for determining the very specific color of an object, regardless of its name. And it is not required to determine whether two objects have the same color.

To determine whether two objects have the same color, an observer would need to view the objects side by side against the same background and under various lighting conditions. If you painted part of a room and find that you don’t have enough paint, for instance, finding a match might be very tricky. A color match requires that no observer under any lighting condition will see a difference between the new paint and the old.

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Is the dress yellow and white or black and blue?

That two people can determine whether two objects have the same color even if they don’t agree on exactly what that color is – just as a pool of water can have a particular temperature without feeling the same to me and you – seems like compelling evidence to us that colors are objective features of our world.

Colors, science and indispensability

Everyday interactions with colors – such as matching paint samples, determining whether your shirt and pants clash, and even your ability to interpret works of art – are hard to explain if colors are not objective features of objects. But if you turn to science and look at the many ways that researchers think about colors, it becomes harder still.

For example, in the field of color science, scientific laws are used to explain how objects and light affect perception and the colors of other objects. Such laws, for instance, predict what happens when you mix colored pigments, when you view contrasting colors simultaneously or successively, and when you look at colored objects in various lighting conditions.

The philosophers Hilary Putnam and Willard van Orman Quine made famous what is known as the indispensability argument. The basic idea is that if something is indispensable to science, then it must be real and objective – otherwise, science wouldn’t work as well as it does.

For example, you may wonder whether unobservable entities such as electrons and electromagnetic fields really exist. But, so the argument goes, the best scientific explanations assume the existence of such entities and so they must exist. Similarly, because mathematics is indispensable to contemporary science, some philosophers argue that this means mathematical objects are objective and exist independently of a person’s mind.

Blue damselfish, seeming iridescent against a black background
The color of an animal can exert evolutionary pressure.
Paul Starosta/Stone via Getty Images

Likewise, we suggest that color plays an indispensable role in evolutionary biology. For example, researchers have argued that aposematism – the use of colors to signal a warning for predators – also benefits an animal’s ability to gather resources. Here, an animal’s coloration works directly to expand its food-gathering niche insofar as it informs potential predators that the animal is poisonous or venomous.

In fact, animals can exploit the fact that the same color pattern can be perceived differently by different perceivers. For instance, some damselfish have ultraviolet face patterns that help them be recognized by other members of their species and communicate with potential mates while remaining largely hidden to predators unable to perceive ultraviolet colors.

In sum, our ability to determine whether objects are colored the same or differently and the indispensable roles they play in science suggest that colors are as real and objective as length and temperature.The Conversation

Elay Shech, Professor of Philosophy, Auburn University and Michael Watkins, Professor of Philosophy, Auburn University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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‘Extraordinary claims require extraordinary evidence’ − an astronomer explains how much evidence scientists need to claim discoveries like extraterrestrial life

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theconversation.com – Chris Impey, University Distinguished Professor of Astronomy, University of Arizona – 2025-04-25 07:54:00

The universe is filled with countless galaxies, stars and planets. Astronomers may find life one day, but they will need extraordinary proof.
ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre (CEA Paris-Saclay), G. Anselmi

Chris Impey, University of Arizona

The detection of life beyond Earth would be one of the most profound discoveries in the history of science. The Milky Way galaxy alone hosts hundreds of millions of potentially habitable planets. Astronomers are using powerful space telescopes to look for molecular indicators of biology in the atmospheres of the most Earth-like of these planets.

But so far, no solid evidence of life has ever been found beyond the Earth. A paper published in April 2025 claimed to detect a signature of life in the atmosphere of the planet K2-18b. And while this discovery is intriguing, most astronomers – including the paper’s authors – aren’t ready to claim that it means extraterrestrial life exists. A detection of life would be a remarkable development.

The astronomer Carl Sagan used the phrase, “Extraordinary claims require extraordinary evidence,” in regard to searching for alien life. It conveys the idea that there should be a high bar for evidence to support a remarkable claim.

I’m an astronomer who has written a book about astrobiology. Over my career, I’ve seen some compelling scientific discoveries. But to reach this threshold of finding life beyond Earth, a result needs to fit several important criteria.

When is a result important and reliable?

There are three criteria for a scientific result to represent a true discovery and not be subject to uncertainty and doubt. How does the claim of life on K2-18b measure up?

First, the experiment needs to measure a meaningful and important quantity. Researchers observed K2-18b’s atmosphere with the James Webb Space Telescope and saw a spectral feature that they identified as dimethyl sulfide.

On Earth, dimethyl sulfide is associated with biology, in particular bacteria and plankton in the oceans. However, it can also arise by other means, so this single molecule is not conclusive proof of life.

Second, the detection needs to be strong. Every detector has some noise from the random motion of electrons. The signal should be strong enough to have a low probability of arising by chance from this noise.

The K2-18b detection has a significance of 3-sigma, which means it has a 0.3% probability of arising by chance.

That sounds low, but most scientists would consider that a weak detection. There are many molecules that could create a feature in the same spectral range.

The “gold standard” for scientific detection is 5-sigma, which means the probability of the finding happening by chance is less than 0.00006%. For example, physicists at CERN gathered data patiently for two years until they had a 5-sigma detection of the Higgs boson particle, leading to a Nobel Prize one year later in 2013.

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The announcement of the discovery of the Higgs boson took decades from the time Peter Higgs first predicted the existence of the particle. Scientists, such as Joe Incandela shown here, waited until they’d reached that 5-sigma level to say, ‘I think we have it.’

Third, a result needs to be repeatable. Results are considered reliable when they’ve been repeated – ideally corroborated by other investigators or confirmed using a different instrument. For K2-18b, this might mean detecting other molecules that indicate biology, such as oxygen in the planet’s atmosphere. Without more and better data, most researchers are viewing the claim of life on K2-18b with skepticism.

Claims of life on Mars

In the past, some scientists have claimed to have found life much closer to home, on the planet Mars.

Over a century ago, retired Boston merchant turned astronomer Percival Lowell claimed that linear features he saw on the surface of Mars were canals, constructed by a dying civilization to transport water from the poles to the equator. Artificial waterways on Mars would certainly have been a major discovery, but this example failed the other two criteria: strong evidence and repeatability.

Lowell was misled by his visual observations, and he was engaging in wishful thinking. No other astronomers could confirm his findings.

An image of Mars in space
Mars, as taken by the OSIRIS instrument on the ESA Rosetta spacecraft during its February 2007 flyby of the planet and adjusted to show color.
ESA & MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA, CC BY-SA

In 1996, NASA held a press conference where a team of scientists presented evidence for biology in the Martian meteorite ALH 84001. Their evidence included an evocative image that seemed to show microfossils in the meteorite.

However, scientists have come up with explanations for the meteorite’s unusual features that do not involve biology. That extraordinary claim has dissipated.

More recently, astronomers detected low levels of methane in the atmosphere of Mars. Like dimethyl sulfide and oxygen, methane on Earth is made primarily – but not exclusively – by life. Different spacecraft and rovers on the Martian surface have returned conflicting results, where a detection with one spacecraft was not confirmed by another.

The low level and variability of methane on Mars is still a mystery. And in the absence of definitive evidence that this very low level of methane has a biological origin, nobody is claiming definitive evidence of life on Mars.

Claims of advanced civilizations

Detecting microbial life on Mars or an exoplanet would be dramatic, but the discovery of extraterrestrial civilizations would be truly spectacular.

The search for extraterrestrial intelligence, or SETI, has been underway for 75 years. No messages have ever been received, but in 1977 a radio telescope in Ohio detected a strong signal that lasted only for a minute.

This signal was so unusual that an astronomer working at the telescope wrote “Wow!” on the printout, giving the signal its name. Unfortunately, nothing like it has since been detected from that region of the sky, so the Wow! Signal fails the test of repeatability.

An illustration of a long, thin rock flying through space.
‘Oumuamua is the first object passing through the solar system that astronomers have identified as having interstellar origins.
European Southern Observatory/M. Kornmesser

In 2017, a rocky, cigar-shaped object called ‘Oumuamua was the first known interstellar object to visit the solar system. ‘Oumuamua’s strange shape and trajectory led Harvard astronomer Avi Loeb to argue that it was an alien artifact. However, the object has already left the solar system, so there’s no chance for astronomers to observe it again. And some researchers have gathered evidence suggesting that it’s just a comet.

While many scientists think we aren’t alone, given the enormous amount of habitable real estate beyond Earth, no detection has cleared the threshold enunciated by Carl Sagan.

Claims about the universe

These same criteria apply to research about the entire universe. One particular concern in cosmology is the fact that, unlike the case of planets, there is only one universe to study.

A cautionary tale comes from attempts to show that the universe went through a period of extremely rapid expansion a fraction of a second after the Big Bang. Cosmologists call this event inflation, and it is invoked to explain why the universe is now smooth and flat.

In 2014, astronomers claimed to have found evidence for inflation in a subtle signal from microwaves left over after the Big Bang. Within a year, however, the team retracted the result because the signal had a mundane explanation: They had confused dust in our galaxy with a signature of inflation.

On the other hand, the discovery of the universe’s acceleration shows the success of the scientific method. In 1929, astronomer Edwin Hubble found that the universe was expanding. Then, in 1998, evidence emerged that this cosmic expansion is accelerating. Physicists were startled by this result.

Two research groups used supernovae to separately trace the expansion. In a friendly rivalry, they used different sets of supernovae but got the same result. Independent corroboration increased their confidence that the universe was accelerating. They called the force behind this accelerating expansion dark energy and received a Nobel Prize in 2011 for its discovery.

On scales large and small, astronomers try to set a high bar of evidence before claiming a discovery.The Conversation

Chris Impey, University Distinguished Professor of Astronomy, University of Arizona

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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Hotter and drier climate in Colorado’s San Luis Valley contributes to kidney disease in agriculture workers, new study shows

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theconversation.com – Katherine Ann James, Associate Professor of Environmental and Occupational Health, University of Colorado Anschutz Medical Campus – 2025-04-25 07:53:00

Agricultural workers exposed to a hotter and drier climate are at an increased risk of kidney damage.
George Rose/via Getty Images

Katherine Ann James, University of Colorado Anschutz Medical Campus

Heat and humidity contributed to kidney damage and disease in the San Luis Valley in Colorado between 1984 and 1998, according to our recently published work in the peer-reviewed journal Weather, Climate, and Society.

The San Luis Valley is the largest high valley desert in North America. Many of its residents work in agriculture and are exposed to worsening air quality. That decline is due to increased wildfires, dust and temperatures, in combination with low humidity. This change was in part caused by the region’s climate becoming more arid due to a 23-year drought.

I’m an environmental epidemiologist with an engineering background. For nearly two decades, I have partnered with the San Luis Valley community to investigate how water systems affect human health. Over the past eight years, my team’s research has focused on the far-reaching human health effects of the drought in the area.

In this study, we used data from a cohort of people in the San Luis Valley who were originally recruited for research on the risk factors for Type 2 diabetes. Researchers often look to established datasets to evaluate new hypotheses because it avoids the need to recruit new study participants. This dataset includes 15 years of clinical, behavioral, demographic, genetic and environmental exposure data. Using it in our recent study allowed us to evaluate the impacts of drought conditions on kidney health.

Our study suggests that a 10% decline in humidity is associated with a 2% increase in risk for acute kidney injury, while accounting for known risk factors for kidney disease. Those risk factors include age, sex, diabetes and hypertension.

These findings are supported by our previous study that examined the effects of drought and heat on emergency and urgent care visits for kidney-related issues between 2003 and 2017 in the San Luis Valley.

The two studies align with growing evidence that climate-related changes, particularly heat and humidity, are contributing to kidney injury. Over time, this means that more people are developing chronic kidney disease.

Why it matters

Globally, 10% of the population has kidney disease. In 2021, kidney diseases were the ninth leading cause of death worldwide, according to the World Health Organization. People experiencing poverty or limited access to health care are disproportionately affected.

In the U.S., more than 1 in 7 adults has chronic kidney disease. That does not account for those with undiagnosed kidney disease.

Extended exposure to drought conditions coupled with inadequate water intake has been linked to kidney stones, acute kidney injury and chronic kidney disease.

Dehydration, especially in outdoor workers who labor in hot or dry conditions, is a known contributor to both acute kidney injury and chronic kidney disease.

Acute kidney injury is characterized by a reduction in kidney function that is reversible.

Chronic kidney disease is kidney damage that is progressive and may not be reversible.

Studies in Florida and California have shown declining kidney health in agriculture workers as working conditions are becoming hotter and drier.

Outdoor workers in agriculture, forestry, mining, ranching and construction are susceptible to the effects of changing outdoor conditions coupled with physical labor. This combination exacerbates dehydration and leads to acute and chronic kidney disease.

What other research is being done

In addition to these studies, our research team is involved in other projects aimed at addressing the health impacts of a changing climate.

One such initiative is the Mountain West Climate-Health Engagement Hub, which focuses on reducing exposure to decreased air quality. This includes the deployment of do-it-yourself air filters and development of low-cost, point-of-use water filters to mitigate exposure to the secondary effects of drought.

Woman tapes a box fan to a box of air filters.
Do-it-yourself air filters can reduce exposure to decreased air quality.
The Washington Post/Getty Images

In the Centers for Health, Work & Environment, where I am affiliated, multiple national and international studies are focused on agriculture workers, farm owners and ranchers.

These studies examine how heat, air quality and drought affect kidney, cardiovascular and mental health. These broader studies aim to inform policy and interventions to safeguard the health of workers globally and particularly in regions most vulnerable to climate change.

The Research Brief is a short take on interesting academic work.The Conversation

Katherine Ann James, Associate Professor of Environmental and Occupational Health, University of Colorado Anschutz Medical Campus

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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