It’s not just how many – it’s when: Global study reveals people judge a potential partner’s sexual history by timing, not total number

A major international study has found that when it comes to choosing a long-term partner, people across the globe consider not just how many sexual partners someone has had, but also when those encounters took place.

Swansea University

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Illustration shows a visual timeline shown to participants, representing a potential partner’s sexual history. Each timeline showed the same number of past partners (12), but with different patterns – some concentrated early in life, others spread evenly, and some decreasing over time.  The study’s findings show that people were more willing to commit to someone whose encounters had become less frequent over time, as seen in timeline 3.

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Credit: Swansea University

This is the first time researchers have explored the timing of sexual history alongside quantity – offering a fresh perspective on human mating psychology.

Led by Swansea University, the study surveyed more than 5,000 participants from 11 countries across five continents. It found that people were generally less willing to commit to someone with a high number of past sexual partners but were more open if those encounters had become less frequent over time, suggesting a shift away from casual sex.

Lead researcher Dr Andrew G. Thomas of Swansea University’s School of Psychology explains: “People use sexual history as a cue to assess relationship risk. In our ancestral past, knowing someone’s sexual history could help people avoid risks like STIs, infidelity, emotional instability, or rivalry with ex-partners.

“Previous studies have shown that people are generally less inclined to pursue relationships with individuals who have had many past sexual partners. However, what’s particularly interesting about this study’s findings is that this effect diminishes when those encounters occurred primarily in the past and this is something we found across the globe."

Participants were shown simple visual timelines representing a potential partner’s sexual history. Each timeline showed the same number of past partners, but with different patterns – some concentrated early in life, others spread evenly, and some decreasing over time. Participants then rated their willingness to pursue a committed relationship, revealing that the timing of past encounters, particularly whether sexual activity with new partners had slowed over time, significantly shaped their perceptions.

Published in Scientific Reports, the study found little evidence of a sexual double standard, with male and female participants evaluating sexual history in similar ways. Only minor sex differences were observed across countries and cultures.

Dr Thomas said: “The results of this study point to a lack of sexual double standards, challenging the idea that women are judged more harshly for their sexual past than men.”

The study also looked at how people’s own attitudes toward casual sex influenced their views. Those who were more open to casual relationships were less affected by a partner’s sexual history, though they still showed some sensitivity to it.

Dr Thomas concludes: “The online discourse around people’s sexual history can be very damning, but the results of this study reveal the picture is far more nuanced. We’ve been led to believe that society harshly judges those with a sexually adventurous past, but as individuals, people are in fact far more forgiving, particularly if someone’s approach to sex has changed.

“The results of this study not only shed light on the universal nature of our sexual psychology but could be used to combat misogynistic discussion of sexual history online.”

—ENDS—

Full study: The paper ‘Sexual partner number and distribution over time affect long-term partner evaluation: Evidence from 11 countries across 5 continents’ is published in Scientific Reports

Image: The attached illustration shows a visual timeline shown to participants, representing a potential partner’s sexual history. Each timeline showed the same number of past partners (12), but with different patterns – some concentrated early in life, others spread evenly, and some decreasing over time.  The study’s findings show that people were more willing to commit to someone whose encounters had become less frequent over time, as seen in timeline 3.

Interview opportunities: Lead author Dr Andrew G. Thomas will consider media requests.

For further information: Kathy Thomas, Swansea University Press Office katherine.thomas@swansea.ac.uk | 01792 295050

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Journal

Scientific Reports

DOI

10.1038/s41598-025-12607-1 

Method of Research

Data/statistical analysis

Subject of Research

People

Article Title

‘Sexual partner number and distribution over time affect long-term partner evaluation: Evidence from 11 countries across 5 continents’

Article Publication Date

31-Jul-2025

 

Fast food, including cheeseburgers and fried chicken, shouldn’t be sold in hospitals, say most Americans in new poll

Physicians Committee for Responsible Medicine

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WASHINGTON, D.C. — Fast food like cheeseburgers, fried chicken, and pizza shouldn’t be sold in hospitals, say most Americans in a new Physicians Committee for Responsible Medicine/Morning Consult poll. The poll comes as a new report from the Physicians Committee—a health advocacy nonprofit with 17,000 doctor members—finds that Chick-fil-A is located in at least 20 U.S. hospitals or medical centers.

When asked, “Do you believe fast food—such as fried chicken, cheeseburgers, or pizza—should be sold in hospitals to patients, visitors, and staff?” 52% of respondents said “no,” and 57% said that hospitals should not profit from fast food sold on their premises. Most respondents, 85%, agreed that these foods do not promote good health. The poll was conducted July 1 to 3, 2025, among 2,202 U.S. adults.

A new report from the Physicians Committee finds that Chick-fil-A is located in at least 20 U.S. hospitals or medical centers, according to the fast-food restaurant’s website.

“While many people consider chicken to be a healthier option than red meat, consuming chicken can increase cholesterol just as much as eating red meat,” says Anna Herby, DHSc, RD, CDCES, who is the nutrition education specialist for the Physicians Committee for Responsible Medicine and oversees the organization’s Healthy Hospital Program. “Hospital staff, visitors, and patients would benefit by choosing more chickpeas and other plant-based foods instead of chicken.”

Consuming chicken has been linked to higher cancer risk, and consuming fried chicken is linked to higher risk of heart disease. Earlier this year, a study found that eating 300 grams of poultry—about the size of a large chicken breast—per week was linked to an increased risk of gastrointestinal cancer and death from all causes. A study published in BMJ found that women who ate fried chicken once or more per day had a 13% higher risk of death from any cause compared with women who did not eat any fried food and a 12% increased risk of death from heart disease.

In 2017, the American Medical Association adopted a resolution calling on hospitals to provide plant-based meals and remove processed meats, such as chicken nuggets, from menus.

“Hospitals should set an example by ensuring that their restaurants serve more menu items that are cholesterol-free, low in saturated fat, and high in fiber-rich vegetables, grains, beans, and fruit,” says Dr. Herby. “Meals like these have been shown to help prevent or improve the chronic diseases that bring people to the hospital.”

The Physicians Committee’s Healthy Hospital Program offers free resources to support institutions that want to make more plant-based options available to patients. With plant-based menu items, inpatient education tools, and printable recipes, patients will be empowered to take control of their health during their hospital stay and beyond. Learn more at PCRM.org/HealthyHospitalProgram.

UofL research shows combined exposure to alcohol and “forever chemicals” increases liver damage

University of Louisville

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Have you ever wondered why some people who drink alcohol develop serious liver problems while others don't? A study from University of Louisville researchers published in May in Toxicological Sciences suggests that the answer might be hidden in everyday sources such as drinking water, food packaging or even non-stick cookware.

Scientists at UofL, along with colleagues from Boston University and the University of Massachusetts Lowell, have identified perfluorooctane sulfonate (PFOS) as a potential environmental factor that worsens alcohol-associated liver disease.

PFOS is a man-made chemical belonging to the group known as per- and polyfluoroalkyl substances (PFAS), often referred to as "forever chemicals" because they do not readily break down in the environment or the human body. These substances have been used for decades in products such as non-stick cookware, water-resistant clothing, fast-food packaging, stain-resistant carpets and upholstery, and firefighting foams. Their extensive use has led to widespread contamination in the environment. Recent data from National Health and Nutrition Examination Survey show that PFAS can be detected in approximately 95% of Americans, sparking increasing concern about their long-term health effects.

At the same time, alcohol consumption remains a significant global health issue. According to the World Health Organization, alcohol contributes to nearly 3 million deaths worldwide each year, and its consumption continues to rise globally. In the U.S. alone, excessive alcohol use is responsible for approximately 95,000 deaths annually, making it one of the leading causes of preventable death and a major contributor to liver disease.

“Given the increasing prevalence of alcohol consumption and the widespread presence of PFAS in the environment, many individuals who drink alcohol may be inevitably exposed to these persistent pollutants. This makes it critically important to study how combined exposures to alcohol and environmental chemicals like PFOS might influence liver health,” said Matthew Cave, UofL professor of medicine and publication co-author.

Although it is well known that both alcohol and PFOS cause liver damage individually, little has been understood about their combined effects until now. Recent studies have shown that only about 35% of heavy drinkers develop severe forms of liver disease, indicating that additional factors such as genetics, sex, microbiome and environmental exposures may contribute to individual susceptibility.

"This work helps explain why two people with similar alcohol consumption may experience very different liver outcomes," said Frederick Ekuban, assistant professor of medicine at UofL and first author of the study. "Environmental exposures like PFOS may be the missing link."

Using animal models, the researchers simulated real-world exposures to both alcohol and PFOS. The study showed that co-exposure to alcohol and PFOS significantly increased fat accumulation and markers of liver damage, as well as clear signs of disrupted metabolism and activation of genes and pathways predicted to be associated with oxidative stress and cancer development.

In short, the study demonstrates that PFOS exposure can significantly worsen liver damage when combined with alcohol consumption. While this research used high levels of alcohol to understand the underlying mechanisms, the findings reveal important biological pathways that warrant further investigation across different drinking patterns.

The research team also found that PFOS interferes with the liver's ability to manage fats, disrupts its natural protective and repair systems and activates pathways that promote liver injury.

“While the liver typically has a remarkable capacity to recover from alcohol-induced stress, PFOS appears to push that resilience beyond its limits, resulting in compounded and more severe damage,” said Jennifer Schlezinger professor of environmental health at Boston University and co-author of the publication.

Perhaps most concerning, the team discovered that 60% of all PFOS exposure ended up concentrated in the liver, exactly where alcohol damage occurs.

Ongoing research at UofL is examining how other PFAS compounds may interact with alcohol, whether males and females respond differently to these exposures and what the long-term consequences of combined exposures might be. The team is also exploring whether targeted therapies can be developed to prevent or mitigate this type of liver damage.

Although more studies are needed, people can take practical steps now to limit their exposure to PFAS. These include:

• Choose stainless steel or cast-iron cookware instead of non-stick pans
• Use water filters, especially in areas near industrial zones
• Avoid stain-resistant treatments on furniture and carpets
• Reduce consumption of packaged fast foods and microwave popcorn.
• Select household products with PFAS-free labels

Given that liver disease affects millions of Americans and is becoming more prevalent worldwide,

the findings of this research support growing calls for stronger regulation and oversight of persistent chemical contaminants. By better understanding the hidden interactions between environmental toxicants and lifestyle behaviors, scientists and policymakers may be better equipped to prevent and treat liver disease.

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Journal

Toxicological Sciences

DOI

10.1093/toxsci/kfaf066/812834 

Method of Research

Experimental study

Subject of Research

Animals

Article Title

Perfluorooctane sulfonate exposure and alcohol-associated liver disease severity in a mouse chronic-binge ethanol feeding model

 

Both flexibility and persistence make some birds successful in human-made environments

University of California - Santa Barbara

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(Santa Barbara, Calif.) — Across North America, grackles are virtuosos of adaptation. The small- to medium-sized New World blackbirds are particularly social and known for foraging skills that help them flourish in environments ranging from rural farms to urban parking lots.

They are often viewed as rather bold and somewhat amusing birds that pick up French fries and other fast food scraps — or, alternatively, as annoying pests that eat our grain crops. 

UC Santa Barbara scientist Corina Logan, however, is fascinated by what goes on in their bird brains and how they manage to adapt to the growing footprint of human-made environments. In a pair of papers that appear in the Peer Community Journal, she and fellow authors investigate the role of behavioral flexibility in great-tailed grackles, a species related to cowbirds and meadowlarks that originated in Central America but has been rapidly expanding its range across the U.S.

“The big question was: Is behavioral flexibility how the great-tailed grackles are so rapidly expanding their geographic range?” said Logan, a research associate at UCSB’s Neuroscience Research Institute who also leads the Comparative Behavioral Ecology Group at the Max Planck Institute for Evolutionary Anthropology. “It is a long-held assumption that this must be the case, but researchers hadn’t yet measured flexibility in populations across the range of a rapidly expanding species.” Their findings provide insight into what needs to be measured to predict how successful species might be in a new environment, which could be a useful tool for conservation managers.

In their first paper, Logan and co-authors define behavioral flexibility as “the ability to change behavior in the face of a changing environment by packaging information and making it available to other cognitive processes.” The cognitive trait is implicated in species range expansion, including early hominids, and also in the adaptations of people who move from one culture to another. However, it has been unclear whether this trait underlies behaviors related to animals’ successful adaptation to new environments, such as foraging, habitat use and sociability.

“The great-tailed grackles are a serendipitous study system about whether flexibility is involved in a rapid geographic range expansion because they happen to be expanding their range,” said Logan, whose group in 2016 discovered that the birds are also highly behaviorally flexible. “This allows us to ask questions like, ‘How does flexibility work? How does it relate to other abilities? Is it the main behavior involved in a range expansion?’”

To answer these questions, the researchers devised two experiments on two distinct populations of great-tailed grackles — one in Tempe, Arizona; the other in Woodland, California. One experiment involved reversal learning, in which the birds were presented with two different colored containers and steered into preferring one color by way of a food reward consistently placed in a container of that color. The food would then be placed in the other container. The speed with which the birds changed their color preference was the measure of flexibility. The researchers then trained one subset of the Arizona population to be more flexible by conducting this process repeatedly.

In the other test, the grackles accessed food through a box of four puzzles. Once the birds solved one puzzle, leading to a food reward, access to the food through that solution would be blocked, requiring the birds to attempt another puzzle. The speed with which they switched locations on the box was the indicator of flexibility. All the birds were then released and observed.

The researchers found that the grackles that had been trained to be more flexible became better at foraging. That is, they ate a wider variety of foods and used more foraging techniques, in effect packaging what they learned during the experiments and deploying it in their usual environments.

“We may laugh at the birds in parking lots eating the leftover French fries, but actually not all birds are able to change their behaviors to take advantage of these human-provided resources,” said Auburn University behavioral ecologist and co-author Kelsey McCune, who conducted the grackle research while she was at UCSB. “So, it’s interesting to find that this ability to eat many different foods is also related to the cognitive trait of behavioral flexibility.”

However, while flexibility underlies foraging behavior, the researchers found no strong correlations between flexibility and sociability between the birds in both the Arizona (trained and untrained) and California (untrained) populations, or between flexibility and habitat use. They hypothesized that this may be because social and habitat use behaviors are “potentially formed early in life and individuals are less likely to change these behaviors when circumstances change.” Another explanation, they said, could be that while their sample sizes allowed them to detect larger effects and medium effects, they were not large enough to detect the weaker and smaller effects.

The second paper compared populations of great-tailed grackles and boat-tailed grackles — birds found along the Atlantic and Gulf coasts of the southeastern U.S., and the great-tailed’s closest relatives.

“Boat-tailed grackles are not rapidly expanding their range,” Logan said. As a result, the expectation was that the boat-tailed grackles would not do as well on the reversal learning test (switching between two different color containers with food) than the great-tailed grackles, or that they would also be less likely to switch between food types.

But when tested, the boat-tailed grackles' reversal learning speeds were within the range of their wider-ranging cousins, and there were no strong differences between the two populations in their ability to switch between food types. “These species are similar in many ways,” Logan said. “They eat the same kinds of foods, live in the same kinds of places, and they even look the same. That they are also similar in their levels of flexibility was surprising, given differences in how fast they are expanding — or not — their ranges.” 

The authors conclude that behavioral flexibility, while helpful in allowing birds to adapt to new food environments, factors into but is not the primary facilitator for geographic range expansion.

Rather, the success of the great-tailed grackle in the expansion of its range may be more attributable to persistence and variability in flexibility, as the researchers point out in previous findings. “It is likely that, historically, both species needed flexibility to adapt to human-modified environments that encroached on their habitat,” Logan explained. ”Perhaps they continue to rely on flexibility to interact in these human-modified environments, which is now their primary habitat.”

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Journal

Peer Community Journal

Article Title

Behavioral flexibility is related to foraging, but not social or habitat use behaviors, in a species that is rapidly expanding its range

 

Biodiversity matters in every forest, but even more in wetter ones

University of Michigan

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 Researchers examined individual trees and their neighbors to quantify diversity for their new study.

This photo shows inside an experimental site in Putuo, China. Individual trees of one species (Triadica sebifera) are surrounded by neighboring trees of another species (Liquidambar formosana).
 

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Credit: Baiyu Yang

Biodiversity is important in every ecosystem. Research has shown having a richer diversity of plant and animal species bolsters ecosystem functioning and stability, making habitats more resilient to the threats of things like pests, disease and climate change.

Still, there are varying degrees of importance. Now, research led by the University of Michigan reveals some of the real-world implications of this fact in forests, providing valuable insights for land managers and conservationists working to protect these habitats.

"Diversity matters everywhere we look," said Peter Reich, professor of environment and sustainability and director of the Institute for Global Change Biology at the University of Michigan. "But in our experiments, we see it matters more in the wetter climates." 

Reich was the senior researcher on a project that encompassed 15 tree diversity experiments across the globe and spanning a range of climates. In an analysis that involved 100,000 trees belonging to nearly 130 species, the researchers found that trees with more diverse neighbors in wetter climates grew more. In drier climates, the effect was weaker or nonexistent.

"This provides a more nuanced insight into how biodiversity works in different environments," said Reich, who is also a professor at the University of Minnesota. "If you're thinking of restoring or regrowing, it makes a lot of sense to plant diverse trees, especially in wetter areas."

Reich stressed that the "wetter" designation includes more than just tropical rainforests that likely come to mind. By the study's metrics, for example, Michigan's forests would also qualify as wet.

The project was enabled by the larger Tree Diversity Network, which is the world's largest network of tree diversity experiments consisting of 34 different sites. The resulting study, published in the journal Nature Ecology & Evolution, included authors from nearly a dozen countries representing more than 30 affiliations. 

The work, likewise, had funding from international sources, including the U.S. National Science Foundation, German Research Foundation, São Paulo Research Foundation and University of Chinese Academy of Sciences.

"We find a tree growth boost in diverse tree neighbourhoods with different species and functional traits—for example, specific leaf area and wood density," said study lead author Liting Zheng, who performed the work as a postdoctoral fellow at Michigan's School of Environment and Sustainability and is now a researcher at the German Center for Integrative Biodiversity Research.

"Our results highlight the importance of establishing and maintaining high neighborhood diversity in forest management—especially to maximize the potential of biodiversity as a nature-based climate solution in wetter regions."

Seeing the forest for the trees

Although previous studies have examined the benefits of biodiversity in the context of climate, their results have been inconsistent. The reasons for that aren't entirely clear, Reich said, but many have shared a couple notable limitations.

For one, they often focused on a single experimental site. Then the few that have used more sites for a more comprehensive analysis tended to quantify biodiversity at a broad level, as a sort of average descriptor of an entire community.

The new study adopted a much more granular approach. Researchers at each experimental site characterized tree biodiversity by looking at every individual and their neighbors.

"What's unique about our study is it has 15 long-term experiments with lots and lots and lots of trees," Reich said. "Then, rather than looking at an entire community, we looked at every individual and eight or so of its neighbors and asked, 'Are those neighbors diverse or not?'"

He added that a limitation of their study is that, because of the nature of the experiments, the trees studied were all fairly young, from 4 to 14 years old. But there's not an obvious argument for why the results wouldn't hold for more mature forests. 

This approach enabled the researchers to show the pronounced impact of biodiversity in wetter forests, as well as make another interesting and important finding. While biodiversity appears to matter more in wetter climates, its impact in wetter years in those wetter climates is negligible. 

"Diversity appears to be better suited for the average condition, which matters for management," Reich said. "There's thinking that biodiversity is really going to help you when you have those extreme years and some evidence supporting this idea, but in our data this was not the case."

Kai Zhu, associate professor of geospatial data science, and Inés Ibáñez, professor of ecosystem science and management—both with Michigan's School of Environment and Sustainability—also contributed to the study.

Researchers used data from 15 tree diversity experimental sites—like this one in Putuo, China—to find that richer diversity promotes more tree growth in wetter climates.

This photograph shows a dense copse of trees growing up a hillside, with trees of different shapes and sizes creating a natural skyline. Most of the trees leaves are a lush green, but some are tinged with a rusty red.

 

Credit

Liting Zheng

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Journal

Nature Ecology & Evolution

DOI

10.1038/s41559-025-02805-5 

Article Title

Neighbourhood diversity increases tree growth in experimental forests more in wetter climates but not in wetter years