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Evolving intelligent life took billions of years − but it may not have been as unlikely as many scientists predicted

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theconversation.com – Daniel Brady Mills, Postdoctoral Fellow in Geomicrobiology, Ludwig Maximilian University of Munich – 2025-02-14 13:33:00

The Sun’s distance from Earth allows it to be habitable for life.
DrPixel/Moment via Getty Images

Daniel Brady Mills, Ludwig Maximilian University of Munich; Jason Wright, Penn State, and Jennifer L. Macalady, Penn State

A popular model of evolution concludes that it was incredibly unlikely for humanity to evolve on Earth, and that extraterrestrial intelligence is vanishingly rare.

But as experts on the entangled history of life and our planet, we propose that the coevolution of life and Earth’s surface environment may have unfolded in a way that makes the evolutionary origin of humanlike intelligence a more foreseeable or expected outcome than generally thought.

The hard-steps model

Some of the greatest evolutionary biologists of the 20th century famously dismissed the prospect of humanlike intelligence beyond Earth.

This view, firmly rooted in biology, independently gained support from physics in 1983 with an influential publication by Brandon Carter, a theoretical physicist.

In 1983, Carter attempted to explain what he called a remarkable coincidence: the close approximation between the estimated lifespan of the Sun – 10 billion years – and the time Earth took to produce humans – 5 billion years, rounding up.

A man wearing a suit with gray hair and a beard.
Brandon Carter is a physicist at the Laboratoire Univers et Théories in Meudon, France.
Brandon Carter/Wikimedia Commons, CC BY-SA

He imagined three possibilities. In one, intelligent life like humans generally arises very quickly on planets, geologically speaking – in perhaps millions of years. In another, it typically arises in about the time it took on Earth. And in the last, he imagined that Earth was lucky – ordinarily it would take much longer, say, trillions of years for such life to form.

Carter rejected the first possibility because life on Earth took so much longer than that. He rejected the second as an unlikely coincidence, since there is no reason the processes that govern the Sun’s lifespan – nuclear fusion – should just happen to have the same timescale as biological evolution.

So Carter landed on the third explanation: that humanlike life generally takes much longer to arise than the time provided by the lifetime of a star.

A diagram showing the life cycle of the Sun, from its birth to its growth into a Red Giant around ten billion years.
The Sun will likely be able to keep planets habitable for only part of its lifetime – by the time it hits 10 billion years, it will get too hot.
NASA/JPL-Caltech

To explain why humanlike life took so long to arise, Carter proposed that it must depend on extremely unlikely evolutionary steps, and that the Earth is extraordinarily lucky to have taken them all.

He called these evolutionary steps hard steps, and they had two main criteria. One, the hard steps must be required for human existence – meaning if they had not happened, then humans would not be here. Two, the hard steps must have very low probabilities of occurring in the available time, meaning they usually require timescales approaching 10 billion years.

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Tracing humans’ evolutionary lineage will bring you back billions of years.

Do hard steps exist?

The physicists Frank Tipler and John Barrow predicted that hard steps must have happened only once in the history of life – a logic taken from evolutionary biology.

If an evolutionary innovation required for human existence was truly improbable in the available time, then it likely wouldn’t have happened more than once, although it must have happened at least once, since we exist.

For example, the origin of nucleated – or eukaryotic – cells is one of the most popular hard steps scientists have proposed. Since humans are eukaryotes, humanity would not exist if the origin of eukaryotic cells had never happened.

On the universal tree of life, all eukaryotic life falls on exactly one branch. This suggests that eukaryotic cells originated only once, which is consistent with their origin being unlikely.

A diagram of a phylogenetic tree, with types of organisms on each branch. On the left are bacteria, in the middle archea and on the right eukaryota.
In the evolutionary tree of life, organisms that have eukaryotic cells are all on the same branch, suggesting this type of cell evolved only once.
VectorMine/iStock via Getty Images Plus

The other most popular hard-step candidates – the origin of life, oxygen-producing photosynthesis, multicellular animals and humanlike intelligence – all share the same pattern. They are each constrained to a single branch on the tree of life.

However, as the evolutionary biologist and paleontologist Geerat Vermeij argued, there are other ways to explain why these evolutionary events appear to have happened only once.

This pattern of apparently singular origins could arise from information loss due to extinction and the incompleteness of the fossil record. Perhaps these innovations each evolved more than once, but only one example of each survived to the modern day. Maybe the extinct examples never became fossilized, or paleontologists haven’t recognized them in the fossil record.

Or maybe these innovations did happen only once, but because they could have happened only once. For example, perhaps the first evolutionary lineage to achieve one of these innovations quickly outcompeted other similar organisms from other lineages for resources. Or maybe the first lineage changed the global environment so dramatically that other lineages lost the opportunity to evolve the same innovation. In other words, once the step occurred in one lineage, the chemical or ecological conditions were changed enough that other lineages could not develop in the same way.

If these alternative mechanisms explain the uniqueness of these proposed hard steps, then none of them would actually qualify as hard steps.

But if none of these steps were hard, then why didn’t humanlike intelligence evolve much sooner in the history of life?

Environmental evolution

Geobiologists reconstructing the conditions of the ancient Earth can easily come up with reasons why intelligent life did not evolve sooner in Earth history.

For example, 90% of Earth’s history elapsed before the atmosphere had enough oxygen to support humans. Likewise, up to 50% of Earth’s history elapsed before the atmosphere had enough oxygen to support modern eukaryotic cells.

All of the hard-step candidates have their own environmental requirements. When the Earth formed, these requirements weren’t in place. Instead, they appeared later on, as Earth’s surface environment changed.

We suggest that as the Earth changed physically and chemically over time, its surface conditions allowed for a greater diversity of habitats for life. And these changes operate on geologic timescales – billions of years – explaining why the proposed hard steps evolved when they did, and not much earlier.

In this view, humans originated when they did because the Earth became habitable to humans only relatively recently. Carter had not considered these points in 1983.

Moving forward

But hard steps could still exist. How can scientists test whether they do?

Earth and life scientists could work together to determine when Earth’s surface environment first became supportive of each proposed hard step. Earth scientists could also forecast how much longer Earth will stay habitable for the different kinds of life associated with each proposed hard step – such as humans, animals and eukaryotic cells.

Evolutionary biologists and paleontologists could better constrain how many times each hard-step candidate occurred. If they did occur only once each, they could see whether this came from their innate biological improbability or from environmental factors.

Lastly, astronomers could use data from planets beyond the solar system to figure out how common life-hosting planets are, and how often these planets have hard-step candidates, such as oxygen-producing photosynthesis and intelligent life.

If our view is correct, then the Earth and life have evolved together in a way that is more typical of life-supporting planets – not in the rare and improbable way that the hard-steps model predicts. Humanlike intelligence would then be a more expected outcome of Earth’s evolution, rather than a cosmic fluke.

Researchers from a variety of disciplines, from paleontologists and biologists to astronomers, can work together to learn more about the probability of intelligent life evolving on Earth and elsewhere in the universe.

If the evolution of humanlike life was more probable than the hard-steps model predicts, then researchers are more likely to find evidence for extraterrestrial intelligence in the future.The Conversation

Daniel Brady Mills, Postdoctoral Fellow in Geomicrobiology, Ludwig Maximilian University of Munich; Jason Wright, Professor of Astronomy and Astrophysics, Penn State, and Jennifer L. Macalady, Professor of Geoscience, Penn State

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

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Trans people affirmed their gender without medical help in medieval Europe − history shows how identity transcends medicine and law

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theconversation.com – Sarah Barringer, Ph.D. Candidate in English, University of Iowa – 2025-02-18 07:36:00

Trans people affirmed their gender without medical help in medieval Europe − history shows how identity transcends medicine and law

The Lady and the Unicorn: Sight.
Unknown/Musée de Cluny, Paris via Didier Descouens/Wikimedia Commons

Sarah Barringer, University of Iowa

Restrictions on medical care for transgender youth assume that without the ability to medically transition, trans people will vanish.

As of 2024, 26 U.S. states have banned gender-affirming care for young people. Less than a month into office, President Donald Trump issued numerous executive orders targeting transgender people, including a mandate to use “sex” instead of “gender” on passports, visas and global entry cards, as well as a ban on gender-affirming care for young people. These actions foreground the upcoming Supreme Court case of U.S. vs. Skrmetti which promises to shape the future of gender-affirming health care in the U.S., including restrictions or bans.

History, however, shows that withholding health care does not make transgender people go away. Scholarship of medieval literature and historical records reveals how transgender people transitioned even without a robust medical system – instead, they changed their clothes, name and social position.

Surgery in medieval times

Surgery was not a widespread practice in the medieval period. While it gained some traction in the 1300s, surgery was limited to southern France and northern Italy. Even there, surgery was dangerous and the risk of infection high.

Cutting off fleshy bits is an old practice and, potential dangers aside, removing a penis or breasts wasn’t impossible. But amputating functioning limbs was nearly always a form of punishment. Medieval people, including surgeons and patients, likely would not have had positive views of surgery that involved removing working body parts.

Watercolor diagram of various implements resembling scalpels
Illustration from a Latin translation of Albucasis’ Chirurgia, depicting surgical instruments.
Wellcome Collection

Surgeons in the 14th century were increasingly thinking about how to perform surgery on those with both male and female genitalia – people now called intersex. But they thought about this in terms of “correcting” genitalia to make it more apparently male or female – an attitude still present today. Historically, the procedure was probably performed on adults, but today it is usually performed on children. Both then and now, the surgery often disregards the patient’s wishes and is not medically necessary, at times leading to complications later. For patients deemed female, excess flesh could be cut away, and for patients deemed male, the vulva could be cauterized to close it.

There is, however, at least one historical example of a transgender individual receiving surgery. In 1300, near Bern, Switzerland, an unnamed woman was legally separated from her husband because she was unable to have sex with him. Soon after, the woman headed to Bologna, which was the surgery capital of Europe at the time. There, a surgeon cut open the woman’s vulva, revealing a penis and testicles. The account ends, “Back home, he took a wife, did rural work, and had legitimate and sufficient intercourse with his wife.”

The story presents the possibility of medical transition, possibly even a desire for it. But given the limits of surgical techniques and ideologies at the time, these forms of medical transition were unlikely to be common.

Transitioning without medicine

To transition without medicine, medieval transgender people relied on changes they could make themselves. They cut their hair, put on different clothes, changed their names, and found new places in society.

In 1388, a young woman named Catherine in Rottweil, Germany, “put on men’s clothes, declared herself to be a man, and called herself John.” John went on to marry a woman and later developed breasts. This caused some initial consternation – the city council of Rottweil sent John and his wife to court. However, the court did not see breasts as inhibiting John’s masculinity and the couple went home without facing any charges.

In 1395, a transgender woman named Eleanor Rykener appeared before a court in London, England, after she was caught working as a prostitute. The court clerk wrote “that a certain Anna … first taught [her] to practice this detestable vice in the manner of a woman. [She] further said that a certain Elizabeth Bronderer first dressed [her] in women’s clothing” and later she took on work as an embroideress and tapster, a sort of bartender. The account is Rykener’s own, but the court clerk editorialized it, notably adding the phrase “detestable vice” in reference to prostitution.

Medieval manuscript illustration of two people embracing in bed
Detail of lovers in bed, Aldobrandino of Siena, Le Régime du corps, northern France. 13th century.
British Library Catalogue of Illuminated Manuscripts/Sloane MS 2435, f. 9v.

Rykener’s account reveals that there were a number of people interested in helping her transition – people who helped her dress, taught her how to behave, provided her employment and supported her choice of a new name. Community was a more important part of her transition than transforming her body. Based on the record, she apparently did not make an effort to create breasts.

Another account appeared in 1355 in Venice, Italy, concerning Rolandina Ronchaia. While John declared himself male, and Rykener was very active in her transition, Ronchaia’s transition was spurred on by the perceptions of others. She argued that she had always had a “feminine face, voice and gestures,” and was often mistaken for a woman. She also had breasts, “in women’s fashion.” One night, a man came to have sex with her, and Ronchaia, “wishing to connect like a woman, hid [her] own penis and took the man’s penis.” After that, she moved to Venice, where, although she continued to wear men’s clothes, she was still perceived as a woman.

Ronchaia’s account is unique because it emphasizes her body and her desire to change it by hiding her penis. But this was still a matter of what she herself could do to express her gender, rather than a medical transition.

A long transgender history

The accounts of medieval transgender individuals are limited – not only in number but in length. A lot of things did not get written down, and people were not talking about transgender people the way we are now.

Historical accounts of transgender individuals are almost always in court records, which reflect the concerns of the court more clearly than the concerns of its subjects. The court was especially worried about sexual activity between men, which both overemphasizes the importance of sex in medieval transgender people’s lives and often obscures that these accounts are even about transgender people. Eleanor Ryekener’s account frequently misgenders her and refers to her as “John.”

But it’s clear that transgender people existed in the medieval period, even when medical care was unavailable to them.

Yellowed page of manuscript with small, inked script
A court document from the interrogation of John Rykener.
Internet Medieval Source Book/Wikimedia Commons

It is also the case that many of these individuals – Rykener is a likely exception – were probably intersex, and their experience would be different from those who were not. Intersex people were legally recognized and allowed some leeway if they chose to transition as an adult. This is starkly apparent in an account from Lille, France, in 1458, where a transgender woman was accused of sodomy and burned at the stake. She claimed “to have both sexes,” but the account says this was not the case. While being demonstrably intersex may not have saved her, that she claimed she was is telling.

Gender transition has a long history, going even further back than the medieval period. Then as now, the local community played a vital role in aiding an individual’s transition. Unlike the medieval period, most modern societies have far greater access to medical care. Despite current restrictions, transgender people have far more options for transition than they once did.

Medieval modes of transitioning are not a solution to current denials of medical care. But medieval transgender lives do illuminate that transgender people will not vanish even when the legal and medical systems strive to erase them.The Conversation

Sarah Barringer, Ph.D. Candidate in English, University of Iowa

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Why community pharmacies are closing – and what to do if your neighborhood location shutters

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theconversation.com – Lucas A. Berenbrok, Associate Professor of Pharmacy and Therapeutics, University of Pittsburgh – 2025-02-18 07:36:00

Why community pharmacies are closing – and what to do if your neighborhood location shutters

Lucas A. Berenbrok, University of Pittsburgh; Michael Murphy, The Ohio State University, and Sophia Herbert, University of Pittsburgh

Neighborhood pharmacies are rapidly shuttering.

Not long ago, Walgreens, one of the nation’s biggest pharmacy chains, announced plans to close 1,200 stores over the next three years. That’s part of a larger trend that has seen nearly 7,000 pharmacy locations close since 2019, with more expected in the coming years.

Many community pharmacies are struggling to stay open due to an overburdened workforce, shrinking reimbursement rates for prescription drugs and limited opportunities to bill insurers for services beyond dispensing medications.

As trained pharmacists who advocate for and take care of patients in community settings, we’ve witnessed this decline firsthand. The loss of local pharmacies threatens individual and community access to medications, pharmacist expertise and essential public health resources.

The changing role of pharmacies

Community pharmacies – which include independently owned, corporate-chain and other retail pharmacies in neighborhood settings – have changed a lot over the past decades. What once were simple medication pickup points have evolved into hubs for health and wellness. Beyond dispensing prescriptions, pharmacists today provide vaccinations, testing and treatment for infectious diseases, access to hormonal birth control and other clinical services they’re empowered to provide by federal and state laws.

Given their importance, then, why have so many community pharmacies been closing?

There are many reasons, but the most important is reduced reimbursement for prescription drugs. Most community pharmacies operate under a business model centered on dispensing medications that relies on insurer reimbursements and cash payments from patients. Minor revenue comes from front-end sales of over-the-counter products and other items.

However, pharmacy benefit managers – companies that manage prescription drug benefits for insurers and employers – have aggressively cut reimbursement rates in an effort to lower drug costs in recent years. As a result, pharmacists often have to dispense prescription drugs at very low margins or even at a loss. In some cases, pharmacists are forced to transfer prescriptions to other pharmacies willing to absorb the financial hit. Other times, pharmacists choose not to stock these drugs at all.

And it’s not just mom-and-pop operations feeling the pinch. Over the past four years, the three largest pharmacy chains have announced plans to close hundreds of stores nationwide. CVS kicked off the trend in 2021 by announcing plans to close 900 pharmacy locations. In late 2023, Rite Aid said that thousands of its stores would be at risk for closure due to bankruptcy. And late in 2024, Walgreens announced its plans to close 1,200 stores over the next three years.

To make matters worse, pharmacists, like many other health care providers, have been facing burnout due to high stress and the lasting effects of the COVID-19 pandemic. At the same time, pharmacy school enrollment has declined, worsening the workforce shortage just as an impending shortfall of primary care physicians looms.

Why pharmacy accessibility matters

The increasing closure of community pharmacies has far-reaching consequences for millions of Americans. That’s because neighborhood pharmacies are one of the most accessible health care locations in the country, with an estimated 90% of Americans living within 5 miles of one.

However, research shows that “pharmacy deserts” are more common in marginalized communities, where people need accessible health care the most. For example, people who live in pharmacy deserts are also more likely to have a disability that makes it hard or impossible to walk. Many of these areas are also classified as medically underserved areas or health professional shortage areas. As pharmacy closures accelerate, America’s health disparities could get even worse.

So if your neighborhood pharmacy closes, what should you do?

While convenience and location matter, you might want to consider other factors that can help you meet your health care needs. For example, some pharmacies have staff who speak your native language, independent pharmacy business owners may be active in your community, and many locations offer over-the-counter products like hormonal contraception, the overdose-reversal drug naloxone and hearing aids.

You may also consider locations – especially corporate-owned pharmacies – that also offer urgent care or primary care services. In addition, most pharmacies offer vaccinations, and some offer test-and-treat services for infectious diseases, diabetes education and help with quitting smoking.

What to ask if your pharmacy closes

If your preferred pharmacy closes and you need to find another one, keep the following questions in mind:

What will happen to your old prescriptions? When a pharmacy closes, another pharmacy may buy its prescriptions. Ask your pharmacist if your prescriptions will be automatically transferred to a nearby pharmacy, and when this will occur.

What’s the staffing situation like at other pharmacies? This is an important factor in choosing a new pharmacy. What are the wait times? Can the team accommodate special situations like emergency refills or early refills before vacations? Does the pharmacist have a relationship with your primary care physician and your other prescribers?

Which pharmacies accept your insurance? A simple call to your insurer can help you understand where your prescriptions are covered at the lowest cost. And if you take a medication that’s not covered by insurance, or if you’re uninsured, you should ask if the pharmacy can help you by offering member pricing or manufacturer coupons and discounts.

What are your accessibility needs? Pharmacies often offer services to make your care more accessible and convenient. These may include medication packaging services, drive-thru windows and home delivery. And if you’re considering switching to a mail-order pharmacy, you should ask if it has a pharmacist to answer questions by phone or during telehealth visits.

Remember that it’s best to have all your prescriptions filled at the same pharmacy chain or location so that your pharmacist can perform a safety check with your complete medication list. Drug interactions can be dangerous.

Community pharmacies have been staples of neighborhoods for more than a century. Unfortunately, current trends in pharmacy closures pose real threats to public health. We hope lawmakers address the underlying systemic issues so more Americans don’t lose access to their medications, health services and pharmacists.The Conversation

Lucas A. Berenbrok, Associate Professor of Pharmacy and Therapeutics, University of Pittsburgh; Michael Murphy, Assistant Professor of Pharmacy Practice and Science, The Ohio State University, and Sophia Herbert, Assistant Professor of Pharmacy, University of Pittsburgh

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Many gluten-free foods are high in calories and sugar, low on fiber and protein, and they cost more − new research

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theconversation.com – Sachin Rustgi, Associate Professor of Molecular Breeding, Clemson University – 2025-02-18 07:36:00

Many gluten-free foods are high in calories and sugar, low on fiber and protein, and they cost more − new research

The vast majority of Americans are not sensitive to foods containing gluten.
Westend61 via Getty Images

Sachin Rustgi, Clemson University

U.S. consumers often pay more for gluten-free products, yet these items typically provide less protein and more sugar and calories compared with gluten-containing alternatives. That is the key finding of my new study, published in the journal Plant Foods for Human Nutrition.

This study compared gluten-free products with their gluten-containing counterparts, and the findings suggested that many perceived benefits of gluten-free products – such as weight control and diabetes management – are exaggerated.

Currently, many gluten-free products lack dietary fiber, protein and essential nutrients. Manufacturers often add supplements to compensate, but the incorporation of dietary fibers during processing can hinder protein digestion.

In addition, gluten-free products generally contain higher sugar levels compared with other products containing gluten. Long-term adherence to a gluten-free diet has been associated with increased body mass index, or BMI, and nutritional deficiencies.

Gluten-free products – defined in the U.S. as those that contain less than or equal to 20 parts per million of gluten – largely lack wheat, rye, barley and sometimes oats, all rich sources of arabinoxylan, a crucial nonstarch polysaccharide. Arabinoxylan provides several health benefits, including promoting beneficial gut bacteria, enhancing digestion, regulating blood sugar levels and supporting a balanced gut microbiota.

Our study also pointed out that it is difficult to find a gluten-free product that excels in all nutritional areas, such as high protein and fiber content with low carbohydrates and sugar.

On the other hand, gluten-free seeded bread contains significantly more fiber – 38.24 grams per 100 grams – than its gluten-containing counterparts. This is likely due to efforts by manufacturers to address fiber deficiencies by using ingredients such as pseudo-cereals, such as amaranth and quinoa hydrocolloids – meaning water-soluble macromolecules used in gluten-free baked goods made with quinoa flour.

These improvements, however, vary by manufacturer and region. For example, gluten-free products in Spain tend to have lower fiber content than their gluten-containing counterparts.

Why it matters

The term “gluten-free diet” has become a buzzword, much like “organic,” and is now a part of everyday life for many people, often without a full understanding of its actual benefits. While a gluten-free diet is a medical necessity for people who are sensitive to gluten, a condition called celiac disease, or for those with wheat allergies, others adopt a gluten-free diet due to perceived health benefits or because it’s a trend.

In 2024, the global gluten-free product market was valued at US$7.28 billion and projected to reach $13.81 billion by 2032. The U.S. market share is estimated to be $5.9 billion – a little less than half of the global figure.

Approximately 25% of the U.S. population consumes gluten-free products. This figure is far higher than the the roughly 6% of people with non-celiac wheat sensitivity, 1% of people with celiac disease and even lower percentages of people with wheat allergies.

This suggests that many people adopt gluten-free diets for reasons other than medical necessity, which may not offer health or financial benefits.

YouTube video
Symptoms of celiac disease and gluten intolerance include stomach pain and bloating.

What’s next

Investment in research and development is essential to create more nutritionally balanced gluten-free products using locally available ingredients. This will require human feeding trials with different formulations of gluten-free products to ensure that these products meet nutritional needs without adverse effects.

Collaborations between governments could help secure subsidies, which would reduce production costs and make these products more affordable. Although the initial costs of research and maintaining a gluten-free production line are high, using local ingredients and financial incentives can make these products more cost-competitive compared with their gluten-containing counterparts.

Public education is also important to keep people informed about the pros and cons associated with a gluten-free diet.

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

Sachin Rustgi, Associate Professor of Molecular Breeding, Clemson University

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

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