Intuition and past research suggest that whether people deem someone trustworthy depends on that person’s past behavior and reputation for betrayal. But now, new work from psychologists at UCLA and Oklahoma State University is helping to explain why people might nevertheless trust certain cheaters and other betrayers.

When we benefit from someone’s betrayal, we tend to still regard that person as inherently trustworthy, the psychologists reported in a study published in Evolution and Human Behavior. Their experiments found that, although subjects tended to regard people who betrayed others as generally less trustworthy, when a person’s betrayal benefited the subject, that person was still thought to be worthy of trust.

At question is the role concepts like “trustworthiness” play in our relationships. According to the research team, inferences about someone’s trustworthiness are used for making adaptive choices — that is, choices that benefit us. So, while people might be attuned to whether someone has betrayed others in the past, the researchers predicted that people would also be attuned to certain relationship-based factors that impact how that person is viewed/trusted.

“Making decisions about whom to trust based only on whether that person has betrayed someone else might not be the best way to determine whether or not I can trust someone,” said study co-author and UCLA professor of psychology Jaimie Krems.

“Sure, if someone betrays other people, that could be a valuable cue that they might betray me — but not always. For example, think about that friend who always tells you other friends’ secrets but doesn’t share yours. This friend is betraying other people but enriching you with information,” Krems added.

This was the researchers’ main contention: The mind should be attuned to whether someone has a reputation for betrayal, yes, but also to how someone’s betrayal affects you.

The researchers designed experiments to test whether people deemed targets more trustworthy when the targets avoided betrayal — but also when the betrayal had different impacts on the subject.

In one series of experiments, participants were randomly assigned to read one of three vignettes describing their interaction with a target. The first experiment involved sharing secrets among friends, while the second involved romantic infidelity. The third described an interaction in the context of international relations, with participants acting as CIA agents attempting to cultivate a French official as a source.

The targets exhibited one of three behaviors: they did not betray anyone when they had the opportunity; they betrayed another person to the participant or betrayed the participant to someone else. For example, some targets did not share a secret, others shared a secret about someone else with the participant, and still others shared the participant’s secret with a third party. After reading the vignettes, participants rated the target’s trustworthiness on a 7-point scale with questions such as, “I would trust the target to keep my secrets.”

As intuition would predict, across all types of relationships, participants regarded targets as more trustworthy if they did not betray anyone and less trustworthy if they did. But people who betrayed were not all deemed equally untrustworthy. When betrayal benefited the participants, they still considered the target trustworthy. This pattern was largely consistent across friendships, romantic relationships and professional relationships.

The findings upheld the researchers’ hypothesis that judgments of trustworthiness are partly a reflection of the person’s disposition and idiosyncratic factors specific to the participant and the person at hand.

The findings show that while people might start with lofty ideals when it comes to trusting people, what they do in practice is often based more on self-interest.

The research was funded by the National Science Foundation.

Key takeaways

• Both intuition and past research suggest that whether people deem someone trustworthy depends on that person’s past behavior and reputation for betrayal.
• In a series of experiments, psychologists found that subjects regarded those who previously exhibited that behavior as less trustworthy. However, when the betrayal benefited them or had no effect on them, participants regarded the betrayer as trustworthy.
• This pattern was largely consistent across the types of relationships studied: friendships, romantic relationships and professional relationships.

The study, published today, January 9, in the journal Nature Water, finds that Earth’s vegetation stores about 786 km³ of water, only about 0.002% of the total amount of freshwater stored on Earth. The study also finds that the time it takes for water to flow through plants (referred to as transit or turnover time) and return to the atmosphere is among the fastest in the global water cycle, ranging from just five days in croplands to 18 days in evergreen needleleaf forests. The transit of water through plants is particularly fast in croplands, grasslands and savannas. The results underscore vegetation’s dynamic role in the water cycle. In comparison to the global annual median of 8.1 days for water to transit through plants from entry to exit, the water in lakes is estimated to take 17 years, and the water in glaciers is estimated to take 1600 years.

“We have known for a long time that most of the water that returns from the ground to the atmosphere does so through plants, but until now, we did not really know how long it took for that water to transit through plants. Our results show that the transit of water through plants occurs on the order of days, rather than months, years, or centuries, as it does in other parts of the water cycle,” said the study’s lead author Dr. Andrew Felton, who carried out the work as part of a U.S. Department of Agriculture Fellowship while at Chapman University and is now a professor at Montana State University.

The research team notes that by combining estimates of the transit of water through plants with the transit of water through the atmosphere (about 8-10 days) and the transit time of water through soil before being taken up by plants (about 60 to 90 days), they can begin to estimate the complete amount of time it takes for a drop of water to move through the terrestrial water cycle.

“Plants are the forgotten part of the global water cycle,” said Felton. “In many cases, plants are not even represented on water cycle diagrams, which is ironic because we already know they play this critical role in returning water from the ground to the atmosphere.”

To generate the estimates, the research team first calculated the amount of water stored in plants using data from NASA’s Soil Moisture Active Passive Mission (SMAP) satellite mission, which provided high-resolution estimates of the water in soils. The SMAP mission originally saw plants as interfering with the soil moisture measurements, and was correcting for their presence. The Chapman researchers found those corrections actually held valuable information for understanding the water cycle. The team combined estimates of plant water storage with cutting-edge estimates of the rates at which water is leaving plants to determine the transit time of water through vegetation. The result was five years of monthly water storage and transit time estimates at a spatial resolution of 9 km².

The research team also found that the transit time of water through vegetation varied considerably across different land cover types, climate and seasons. The transit time of water through croplands was significantly and consistently the fastest, with water transiting through plants in less than a day during the peak of the growing season.

“One important observation is that croplands around the world tend to have very similar and very fast transit times,” said Dr. Gregory Goldsmith, senior author and an associate professor of Biological Sciences at Chapman University. “This indicates that land use change may be homogenizing the global water cycle and contributing to its intensification by more rapidly recycling water back to the atmosphere where it can turn into heavy rain events.”

“The results suggest that the transit time of water through plants is likely to be very sensitive to events such as deforestation, drought and wildfire, which will fundamentally change the time it takes for water to flow through the water cycle,” Felton said.

The findings were made available online ahead of the next print edition of the journal Zoonoses and Public Health. Given the proximity of dogs to humans and the use of critically important antibiotics in companion animal medicine, the researchers reported, household dogs represent a risk for the spread of antimicrobial-resistant Salmonella. They explained that better awareness of the risk and proper hygiene could potentially help mitigate cross-species infections.

Salmonella infections in dogs can be clinical — showing signs or symptoms — or asymptomatic with numerous studies reporting Salmonella isolation from clinically healthy dogs, according to team leader Erika Ganda, assistant professor of food animal microbiomes, Penn State College of Agricultural Sciences. A major concern, she explained, is the closeness of humans and pet dogs that creates ample opportunity for Salmonella “zoonosis” — the disease transmitted to humans from animals — and pet-management decisions involving food contamination, improper food handling or both can increase the likelihood of infection.

To investigate antimicrobial-resistant Salmonella and the zoonotic potential of nontyphoidal Salmonella isolated from dogs and humans, the researchers leveraged existing biosurveillance infrastructure. Using the U.S. Food & Drug Administration’s Veterinary Laboratory Investigation and Response Network, they identified all nontyphoidal Salmonella strains isolated from domestic dogs between May 2017 and March 2023.

Then they matched the timing and location of those 87 cases to strains isolated from humans in the National Center for Biotechnology Information database maintained by the National Library of Medicine at the National Institutes of Health, which provides access to biomedical and genomic information. They found 77 suspected zoonotic cases — meaning the bacteria moved from a pet dog to a human — comprising 164 strains, collected from 17 states in the United States.

Strains isolated from dogs included diverse serovars, or distinct variations within the species of bacteria, with most being clinically relevant to human health, the researchers reported. While the datasets did not contain information on severity of infection or treatments, the researchers did find that all identified strains possessed antimicrobial resistance genes for drug classes deemed critically or highly important by the World Health Organization.

“We identified 16 nontyphoidal Salmonella isolates from humans closely related to more than one of six dog-associated strains,” said Sophia Kenney, a student in the molecular, cellular and integrative biosciences doctoral program, and in the Department of Animal Science, who spearheaded the study. “Collectively, our data emphasize the importance of antimicrobial stewardship and sustained biosurveillance beyond human and agriculture-associated veterinary medicine, using a ‘One Health’ framework, that accounts for all transmission points — including companion animals. One Health isan approach that recognizes that the health of people is closely connected to the health of animals and our shared environment.”

Antimicrobial stewardship in companion animal veterinary medicine is crucial for mitigating antimicrobial resistance within the One Health model, Kenney explained.

“Especially with Salmonella, we think about the role of agriculture and transmission — we think about eggs, we think about beef. But the thing is, we don’t let cows sleep in our beds or lick our faces, but we do dogs,” she said. “We have this close bond with companion animals in general, and we have a really close interface with dogs. So, we asked the question: What’s the role of companion animals in transmission of zoonotic disease like Salmonella, since they can get it. Salmonella infections in dogs are not common but we’re aware of foodborne outbreaks related to pet treats or from contact with contaminated pet food and improper food handling.”

Study co-author Nkuchia M’ikanatha, lead epidemiologist for the Pennsylvania Department of Health and an affiliated researcher in Penn State’s Department of Food Science, referred to an outbreak of multidrug-resistant Salmonella infections in people linked to pig ear pet treats in the United States a few years ago that sickened 154 people across 34 states.

“This reminds us that simple hygiene practices such as hand washing are needed to protect both our furry friends and ourselves — our dogs are family but even the healthiest pup can carry Salmonella,” he said. “Salmonella is a quintessential human microbe, its presence intertwined with our history since the dawn of agriculture. Emerging research suggests this pathogen may have shadowed humanity for some 10,000 years, coinciding with the rise of animal domestication. With nearly 40% of Pennsylvania households and over half of U.S. homes including dogs, we must respect the enduring threat of Salmonella and remain vigilant in preventing its spread within our families.”

Bacteria are never entirely “bad” or “good” — their role depends on the context, Ganda pointed out. While some bacteria, like Salmonella, can pose serious health risks, others are essential for maintaining our health and the health of our pets. It is important to remain vigilant and informed about potential risks, especially when living closely with animals, she added.

“At the same time, several studies highlight the significant physical and mental health benefits of owning a dog, including reduced stress and increased physical activity,” Ganda said. “Our goal is not to discourage pet ownership but to ensure that people are aware of potential risks and take simple steps, like practicing good hygiene, to keep both their families and their furry companions safe.”

This work was supported by funds from the U.S. Department of Agriculture, the U.S. Centers for Disease Control and Prevention, the National Institutes of Health and the U.S. Food and Drug Administration.