Coincidence? Not likely, finds new research by anthropologist and professor Douglas Kennett of UC Santa Barbara.

Writing in the journal Nature Communications, lead author Kennett and collaborators in the fields of archaeology, history, geography and earth science suggest that drought may in fact have stoked the civil conflict that begat violence, which in turn led to the institutional instabilities that precipitated Mayapan’s collapse. This transdisciplinary work, the researchers said, “highlights the importance of understanding the complex relationships between natural and social systems, especially when evaluating the role of climate change in exacerbating internal political tensions and factionalism in areas where drought leads to food insecurity.”

“We found complex relationships between climate change and societal stability/instability on the regional level,” Kennett said in an interview. “Drought-induced civil conflict had a devastating local impact on the integrity of Mayapan’s state institutions that were designed to keep social order. However, the fragmentation of populations at Mayapan resulted in population and societal reorganization that was highly resilient for a hundred years until the Spanish arrived on the shores of the Yucatan.”

The researchers examined archaeological and historical data from Mayapan, including isotope records, radiocarbon data and DNA sequences from human remains, to document in particular an interval of unrest between 1400 and 1450 CE. They then used regional sources of climatic data and combined it with a newer, local record of drought from cave deposits beneath the city, Kennett explained.

“Existing factional tensions that developed between rival groups were a key societal vulnerability in the context of extended droughts during this interval,” Kennett said. “Pain, suffering and death resulted from institutional instabilities at Mayapan and the population fragmented and moved back to their homelands elsewhere in the region.”

The vulnerabilities revealed in the data, the researchers found, were rooted in Maya reliance on rain-fed maize agriculture, a lack of centralized, long-term grain storage, minimal investments in irrigation and a sociopolitical system led by elite families with competing political interests.

Indeed the authors argue that “long-term, climate-caused hardships provoked restive tensions that were fanned by political actors whose actions ultimately culminated in political violence more than once at Mayapan.”

Yet significantly, a network of small Maya states also proved to be resilient after the collapse at Mayapan, in part by migrating across the region to towns that were still thriving. Despite decentralization, trade impacts, political upheaval and other challenges, the paper notes, they adapted and persisted into the early 16^th century. It all points to the complexity of human responses drought on the Yucatan Peninsula at that time — an important consideration for the future as well as the past.

“Our study demonstrates that the convergence of information from multiple scientific disciplines helps us explore big and highly relevant questions,” Kennett said, “like the potential impact of climate change on society and other questions with enormous social implications.

“Climate change worries me, particularly here in the western U.S., but it is really the complexities of societal change in response to climatic perturbations that worry me the most,” he added. “The archaeological and historical records provide lessons from the past, and we also have so much more information about our Earth’s climate and the potential vulnerabilities in our own sociopolitical systems.”

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Materials provided by University of California – Santa Barbara. Original written by Shelly Leachman. Note: Content may be edited for style and length.

“Based upon over a decade of data, cannabis use was markedly more prevalent in states where recreational use is legal for adults, relative to states where it was not in 2017. Yet, the increases in cannabis use during this time period were as fast, or faster, in states where cannabis use is prohibited by law, relative to states that had legalized for recreational use by 2017,” said Renee Goodwin, PhD, adjunct associate professor of epidemiology at Columbia Mailman School and professor of epidemiology at CUNY, and lead author. “It remains to be seen how increased lawful accessi and growing use of cannabis among adults in all states — almost regardless of legal status — will impact the adolescent population. Recent trends, however, outline a potential explosion in both of-age and under-age use,” she noted.

The researchers used data from the 2004-2017 National Survey on Drug Use and Health, a representative survey of U.S. individuals aged 12 and older. State of residence was used to determine state-level medical and recreational cannabis laws. The total sample was 784,293 respondents and for 2017 was 56,276 respondents.

The study found that cannabis use and daily cannabis use increased in the U.S with little difference in the speed of increase by state-level legal status of cannabis use from 2004 through 2017. Cannabis use and daily cannabis were much more common in states with recreationally legal cannabis use, relative to those with legal medical cannabis and those with no legal cannabis use.

Cannabis use was even greater among Americans who also smoke cigarettes in states that had adopted recreational cannabis laws, relative to those where cannabis use was not legal. In 2017, one in three (33 percent) daily cigarette smokers reported cannabis use in the past month in recreationally legal states and almost one in five (18 percent) reported daily cannabis use. In contrast, among non-smokers, one in ten reported any cannabis use in recreationally legal states and 3 percent of non-cigarette smokers in these states reported daily use.

The study found that among adolescents ages 12-17 who used cigarettes daily, the majority (73 percent) had used cannabis in the past month and almost one in three (30 percent) used cannabis daily. Among adolescents who did not smoke cigarettes, 5 percent used cannabis in the past month and one percent used cannabis daily.

The study is published online in the journal Drug and Alcohol Dependence.

Goodwin observes, “U.S. states are rapidly passing legislation, yet what should be requisite public education on how cannabis can be used safely has not accompanied these changes. For instance, retail licenses are being issued and it is expected that recreational retail outlets will open within the year in New York State, yet New York has not provided evidence-based guidance outlining safe cannabis use practices or informing the public of potential health risks associated with various levels of cannabis use.”

Co-authors are Katarzyna Wyka, City University of New York and Andrea Weinberger, Yeshiva University.

The study was supported by National Institutes of Health/National Institute on Drug Abuse (grant number R01-DA20892).

Won, assistant professor of genetics and member of the UNC Neuroscience Center, and colleagues identified genes linked to cigarette smoking and drinking. The researchers found that these genes are over-represented in certain kinds of neurons — brain cells that trigger other cells to send chemical signals throughout the brain.

The researchers, who published their work in the journal Molecular Psychiatry, also found that the genes underlying cigarette smoking were linked to the perception of pain and response to food, as well as the abuse of other drugs, such as cocaine. Other genes associated with alcohol use were linked to stress and learning, as well as abuse of other drugs, such as morphine.

Given the lack of current treatment options for substance use disorder, the researchers also conducted analyses of a publicly available drug database to identify potential new treatments for substance abuse.

“We found that antipsychotics and other mood stabilizers could potentially provide therapeutic relief for individuals struggling with substance abuse,” said Nancy Sey, graduate student in the Won lab and the first author of the paper. “And we’re confident our research provides a good foundation for research focused on creating better treatments to address drug dependency.”

Parsing the Genome

Long-term substance use and substance use disorders have been linked to many common diseases and conditions, such as lung cancer, liver disease, and mental illnesses. Yet, few treatment options are available, largely due to gaps in our understanding of the biological processes involved.

“We know from twin studies that genetics may account for why some people use and abuse substances, aside from environmental factors, such as family issues or personal trauma,” Won said. “Genetic studies such as genome-wide association studies (GWAS) provide a way to identify genes associated with complex human traits, such as nicotine addiction or drinking heavily.”

Through GWAS, Won added, researchers can identify regions in the genome that play roles in particular traits, compared to individuals who do not exhibit the trait. Yet, genome-wide studies cannot tell us much about how genes in those regions affect a trait. That’s because these regions are often in “non-coding” regions of the genome.

“Non-coding” refers to the fact that the genes in these regions do not translate — or code — their genetic information directly into the creation of proteins, which then perform a known biological function. Therefore, what actually happens biologically in these “non-coding” regions remains mostly unknown.

“We wanted to learn what’s happening in these regions,” Won said. “So we developed Hi-C coupled MAGMA (H-MAGMA), a computational tool to help us make more sense of what we’re seeing in genome-wide studies.”

In a previous publication, Won’s lab showed how applying H-MAGMA to brain disorders identifies their associated genes and described their underlying biology. And for this current paper, her lab expanded the tool to cigarette smoking and drinking.

They developed H-MAGMA frameworks from dopaminergic neurons and cortical neurons — brain cell types that researchers have long implicated in substance use. Focusing on those two cell types, Won’s team — led by Sey, an HHMI Gilliam Fellow — applied H-MAGMA to GWAS findings related to heaviness of smoking, nicotine dependence, problematic alcohol use, and heaviness of drinking to identify genes associated with each trait.

Genes associated with alcohol use and cigarette smoking were also associated with other types of substances, such as morphine and cocaine. While the opioid crisis has caused a detrimental social burden, well-powered GWAS on cocaine and opioid use are not currently available. Won’s team, therefore, sought to determine whether the genes associated with alcohol use and cigarette smoking can reveal genetics underlying general addiction behavior, genetic findings that could be extended to other substances of abuse.

“Our analyses showed that expression of genes shared between cigarette smoking and alcohol use traits can be altered by other types of substances such as cocaine,” Won said. “By characterizing the biological function of these genes, we will be able to identify the biological mechanisms underlying addiction, which could be generalized to various forms of substance use disorder.”

In addition to the various types of excitatory neurons, Won’s team also identified additional cell types, including cortical glutamatergic, midbrain dopaminergic, GABAergic, and serotonergic neurons that are associated with the risk genes.

With these findings in hand, it is now possible for the UNC researchers and others to investigate molecules that make addiction much less likely.

This research was supported through grants from the National Institute on Drug Abuse (R21DA051921, U01DA048279); the National Institute of Mental Health (R00MH113823, DP2MH122403); the NARSAD Young Investigator Award from the Brain and Behavior Research Foundation; the National Science Foundation Graduate Research Fellowship Program (DGE-1650116); the University of North Carolina at Chapel Hill; the Howard Hughes Medical Institute’s James H. Gilliam Fellowship for Advanced Study Program; and the National Institute of General Medical Sciences (5T32GM067553).