Why Classic Maya cities rose and fell

New study reveals the forces that built and collapsed ancient urban centers — and how they echo in today’s urban challenges

University of California - Santa Barbara

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Why move to a city? And why leave? Urban centers today see populations ebb and flow for a multitude of reasons — the economy, crowds, lifestyle considerations, air quality, the odd pandemic perhaps.

Turns out it’s sort of always been that way.

The earliest cities worldwide were born of country folk. Farmers, that is, agriculturists. They were agrarian populations, reliant on land-extensive economies, which incentivized them to live dispersed across the landscape in small settlements, to minimize the time and travel costs between their residences and farm plots.

Then as now, though, city living was more expensive in all the ways: greater susceptibility to crowd diseases, greater competition for land and resources and rising levels of systemic inequality. And still farmers chose to bear these seemingly paradoxical costs.

What gives?

That question has been the source of a long-standing debate, according to UC Santa Barbara archaeologist Douglas Kennett, who has conducted extensive research into urbanization in Classic Maya cities. The answer, he said, is complicated, suggesting there are multiple, often overlapping factors for both the rise and the fall of these ancient urban centers.

Kennett and collaborators from several institutions explore and elucidate that complexity in a new study, published in the Proceedings of the National Academy of Sciences. The research leverages population ecology theory and quantifies the drivers of urbanism across the Classic Maya Lowlands.

“We determined that the rise and expansion of Classic Maya cities resulted from the interaction of climate downturns, intergroup conflict and the presence of strong economies of scale realized through capital investments in agricultural infrastructure,” Kennett said. “These factors promoted the coevolution of urbanism, systemic inequality and patron-client relationships in cities.”

Using that same framework, he added, the researchers also determined that deurbanization set in “when the benefits of urban living no longer outweighed the costs, as environments were degraded near cities and climate amelioration improved the livability of rural areas where people would have more freedom and autonomy.”

Indeed, the team’s initial interest was centered on the role of climate change — specifically drought — in the decline of Classic Maya cities. Since 2012 the group has been amassing archaeological data on changing population sizes, conflict and investments in agricultural infrastructure. Then they came into some newly available high-resolution climatic data. 

“We also capitalized on major developments in computational modeling that allowed us to look at the relationships between these datasets in ways not previously possible,” Kennett said. 

Their results integrate previously contentious and separate theories of urbanization — such as environmental stress, warfare and economic factors — into a single, dynamic model based on concepts from population ecology. The study also resolves the paradox of why agrarian populations — whose land-extensive economy incentivizes dispersal — would aggregate despite the high costs of urbanization.

“The biggest surprise for me was that the abandonment of cities occurred under improving climatic conditions,” Kennett noted. “We have long thought that the decline of Classic Maya cities partially resulted from an extended period of drought. It turns out to be a much more complicated and interesting story.”

All told, the new work offers critical insights for understanding and managing contemporary and future urban evolution by establishing timeless, universal principles for how populations aggregate and disperse.

 

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2512325122 

Article Title

Modeling the rise and demise of Classic Maya cities: Climate, conflict, and economies of scale

Article Publication Date

16-Oct-2025

 

Sleep practices during infant illnesses may increase risk of sudden infant death

Johns Hopkins Medicine

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When a child falls ill, caregivers often change how and where the infant sleeps — wanting to keep them close through the night. But new research from Johns Hopkins Children’s Center suggests that some of these changes — although well-intentioned — contradict proven safe sleep practices for infants, and may do more harm than good. 

In interviews with more than 100 caregivers of infants ages birth to 12 months presenting to the emergency department for infant illness, researchers found that unsafe sleep practices became more common during periods of illness — and often persisted even after the illness resolved. These changes to sleep practices increase an infant’s risk of sudden unexpected infant death (SUID), a broad term that includes sudden infant death syndrome (SIDS). SUID, defined as the unexpected sudden death of a seemingly healthy infant from known and unknown causes, resulted in the deaths of 3,700 infants in 2022, according to federal health statistics. 

Numerous studies over past decades have tied unsafe sleep practices to both SIDS and SUID. Findings from the new study, funded by the National Institutes of Health, were published Sept. 18 in Pediatrics, and add to evidence that infant illness is a risk factor for SUID. 

Caregivers were asked about the infants’ usual sleep practices, and if they changed when the babies were sick. The caregivers reported that adherence to safe habits, such as putting their infants in a crib or Pack ’n Play, declined overall from 61.8% before illness to 48.1% during illness. In addition, the proportion of caregivers reporting their infants sleeping in a bed or on a couch rose from 56.5% before illness to 62.6% during illness, and further increased to 75% at the one-month follow-up. Similarly, bed-sharing rates increased overall from 57.3% before illness to 68.7% during illness, and further increased to 83.6% at the one-month follow-up. 

Many caregivers in the study reported shifts away from recommended safe sleep practices, such as placing infants on their backs to sleep, during infant illness. The most common changes included increased bed-sharing, sleeping on non-recommended sleep surfaces, and prone or side positioning, which are not in line with the American Academy of Pediatrics safe sleep recommendations. 

The fact that the alterations persisted beyond the illness period highlights the need for targeted interventions to reinforce safe sleep practices during illness, says Mary Beth Howard, M.D., M.Sc., pediatric emergency medicine physician at Johns Hopkins Children’s Center and lead researcher on the study. 

“Parents often make these changes because they want to comfort or closely watch their sick baby, but these well-intentioned adjustments actually raise the risks of sudden, unexpected death. Illness is a particularly vulnerable time, making it even more important to stick to safe sleep guidelines,” says Howard. 

The Johns Hopkins investigators note that October is Sudden Infant Death Syndrome (SIDS) Awareness Month, a time to encourage safe infant sleep practices. According to the American Academy of Pediatrics, safe sleep practices include placing infants on their backs to sleep, having infants sleep alone without blankets, pillows or stuffed animals, and having babies sleep in a crib or bassinet. 

Additional experts who contributed to this research include Leticia Ryan, Kevin Psoter, Barry Solomon, Milind Mutala and Sarah Ehrenberg from Johns Hopkins and Rachel Moon from University of Virginia.

The authors have no conflicts of interest relevant to this article to disclose.

Funding for this research was provided by the National Center for Advancing Translational Sciences (KL2TR003099) and the Johns Hopkins University School of Medicine Biostatistics, Epidemiology and Data Management Core.

For more information about Johns Hopkins research and how it saves lives, visit the Johns Hopkins Children’s Center and Johns Hopkins All Children’s Hospital Research Saves Children website.

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Journal

PEDIATRICS

 

Study of incarcerated women in Chile, substance use disorders were associated with higher rates of recidivism, reincarceration, victimization

Fewer than 10% of women studied had received mental health services

Rutgers University Newark School of Criminal Justice

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Mental health disorders are more prevalent among incarcerated individuals than in the general population, and disorders related to substance use are especially prevalent among incarcerated women. Yet little research has focused on how women’s mental health changes or persists following incarceration and during re-entry.

In a new study, researchers explored the mental health of incarcerated women in Santiago, Chile, before they were released and at several times after release. Most women’s mental health symptoms were stable during the first year after release, but pre-release screening missed women with increasingly severe symptoms and with substance dependency during re-entry. In addition, women were provided mental health care services at alarmingly low rates, researchers found.

The study was conducted by researchers at Rutgers University-Newark, New York University (NYU), Pontificia Universidad Católica de Chile, Fundación Colunga, and Universidad Diego Portales. It is published in Social Psychiatry and Psychiatric Epidemiology.

“The almost 20% of women in our study with persistent substance use disorders had higher rates of recidivism, arrests, reincarceration, and victimization after being released,” says Pilar Larroulet, assistant professor of criminal justice at Rutgers University-Newark, who coauthored the study. “Addressing these disorders is particularly important due to their high prevalence in this population and to their role in women’s successful re-entry into society.”

In Chile, women make up less than 10% of the prison population but have experienced a more rapid rise in incarceration rates and higher rates of turnover (returning to prison after release) than men. As in other countries, incarcerated women come primarily from disadvantaged communities, and compared to men, have lower levels of education, are older, and are more likely to have children. They are also at greater risk of mental health disorders.

In this work, researchers interviewed 200 Chilean women released from prison facilities in Santiago between September 2016 and March 2017. The women had served custodial sentences of at least 30 days and were released on parole or finished their sentence. Researchers assessed them based on three indicators of mental health: a checklist of symptoms before release and one week, two months, six months, and a year after release; self-reported suicide attempts; and substance use dependence.

Researchers divided the women into three groups based on the trajectories of their mental health-related symptoms after release: 86% had a stable low severity trajectory, nearly 7% reported increasing severity, and more than 7% had a high and stable trajectory of severe symptoms. Women in the study had been highly victimized prior to their most recent incarceration, with almost half having suffered some sort of sexual abuse and only one in 10 saying they had never experienced physical violence.

Experiences of victimization were associated with having increasingly severe symptoms, suicidal attempts, and persistent substance dependence. In addition, women who said they had attempted suicide and had persistent substance use dependence self-reported substantially more victimization during follow-up interviews. The study also found that:

• For most women released from prison, mental health symptoms appeared to remain stable over the first year after release, with fewer than 10% showing an increase in symptoms over time.
• Nine out of 10 women self-reported lifetime physical violence and more than a third said they were victimized after release.
• Nearly a fifth of the women said they attempted suicide after they were released and nearly a fifth met the criteria for substance use dependence at both baseline and one year later.
• Nearly half of the women committed crimes after they were released—most of them minor property offenses such as theft, and nearly a quarter were reincarcerated.
• Only 10% or fewer reported receiving mental health services at any time they were assessed.

Although for most of the women, the severity of mental health symptoms decreased immediately after release, pre-release screening missed women with increasing severity of symptoms and substance use, the study found. This is likely because most incarcerated individuals leave the criminal justice system without being assessed for mental health problems, even when they show symptoms. The specific needs of women are often overlooked due to their minority status in the criminal justice system, despite evidence suggesting that women express the need for services.

Women with increasing and high levels of severity of mental health systems had more previous sentences, more reported suicidal attempts after release, more persistent substance dependence, and more recidivism. These findings are consistent with the revolving door hypothesis, which posits that people with short sentences and high reincarceration rates present more mental health care needs. Alternatives to incarceration, including community-based treatments and programs, should be considered for these individuals, the authors suggest.

“The success of re-entry depends on the resources of individuals, communities, and broader societal structures,” explains Ignacio Bórquez, Ph.D. candidate at NYU’s Grossman School of Medicine, who coauthored the study. “Incarceration could act as a touch point to provide gender- and trauma-informed care to people who are otherwise difficult to reach.”

Among the study’s limitations, the authors note that the number of women studied was relatively small and the study relied on self-reports on sensitive topics, which may introduce bias. In addition, interviewing the women one year after they were released may not have captured long-term changes in their mental health outcomes and use of services.

The study was funded by the San Carlos de Maipo and Colunga Foundation, the Inter-American Development Bank, the Division on Women and Crime from the American Society of Criminology, Agencia Nacional de Investigación y Desarrollo Millennium Science Initiatives, and  FONDECYT Chile.

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Journal

Social Psychiatry and Psychiatric Epidemiology

DOI

10.1007/s00127-025-02849-9 

Article Title

Trajectories of mental health symptoms, suicide attempts and substance use disorders among women after prison release in Santiago, Chile

 

Non-hibernating pikas' protein restriction tweaks their gut microbiome to help them survive the winter, when winter-active herbivores often struggle to find dietary protein

PLOS

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image: 

A plateau pika (Ochotona curzoniae) foraging during the harsh winter on the Qinghai-Tibet Plateau.

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Credit: Dr. Fuyu Shi (CC-BY 4.0, https://creativecommons.org/licenses/by/4.0/)

Non-hibernating pikas' protein restriction tweaks their gut microbiome to help them survive the winter, when winter-active herbivores often struggle to find dietary protein

In your coverage, please use this URL to provide access to the freely available paper in PLOS Biology: https://plos.io/4nI13TV

Article title: Increased urea nitrogen salvaging by a remodeled gut microbiota helps nonhibernating pikas maintain protein homeostasis during winter

Author countries: China, Israel

Funding: see manuscript

A plateau pika (Ochotona curzoniae) at the burrow entrance in late September.

Credit

Dr. Qingsheng Chi (CC-BY 4.0, https://creativecommons.org/licenses/by/4.0/)

Journal

PLOS Biology

DOI

10.1371/journal.pbio.3003436 

Method of Research

Experimental study

Subject of Research

Animals

COI Statement

Competing interests: The authors have declared that no competing interests exist.