Bat die-offs in the U.S. led to increased use of insecticides, which in turn led to greater infant mortality, according to a "seminal" study published Thursday that shows the effects of biodiversity loss on human beings.

Eyal Frank, an environmental economist at the University of Chicago, authored the study, which was published by Science, a leading peer-reviewed journal.

Bats can eat thousands of insects per night and act as a natural pest control for farmers, so when a fungal disease began killing off bat populations in the U.S. after being introduced in 2006, farmers in affected counties used more insecticides, Frank found. Those same counties saw more infant deaths, which Frank linked to increased use of insecticide that is harmful to human health, especially for babies and fetuses.

The study was greeted by an outpouring of praise from unaffiliated scientists for its methodology and the important takeaways it offers.

"[Frank] uses simple statistical methods to the most cutting-edge techniques, and the takeaway is the same," Eli Fenichel, an environmental economist at Yale University, toldThe New York Times. "Fungal disease killed bats, bats stopped eating enough insects, farmers applied more pesticide to maximize profit and keep food plentiful and cheap, the extra pesticide use led to more babies dying. It is a sobering result."

Carmen Messerlian, an environmental epidemiologist at Harvard University, told the Times the study "seminal" and "groundbreaking."

The study shows the need for a broader understanding of human health that includes consideration of entire ecosystems, said Roel Vermeulen, an environmental epidemiologist at Utrecht University in the Netherlands. "It emphasizes the need to move from a human-centric health impact analysis, which only considers the direct effects of pollution on human health, to a planetary health impact assessment," he toldNew Scientist.

Reporter Benji Jones echoed that sentiment in Vox, calling Frank's findings "astonishing" and writing that such studies could help us fight chemical pollution by corporations.

"When the link between human and environmental health is overlooked, industries enabled by short-sighted policies can destroy wildlife habitats without a full understanding of what we lose in the process," Jones said. "This is precisely why studies like this are so critical: They reveal, in terms most people can relate to, how the ongoing destruction of biodiversity affects us all."

Frank, who said he started the work after stumbling on an article about bat population loss while procrastinating, happened upon an excellent natural experiment. The spread of white-nose syndrome, the fungal disease, was well tracked on a county-by-county level, leaving him with high-quality data that is hard to find for researchers who study the intersection of human and animal life.

The benefits of biodiversity on humans, and the drawbacks to its loss, are normally very difficult to quantify.

"That's just quite rare—to get good, empirical, grounded estimates of how much value the species is providing," Charles Taylor, an environmental economist at Harvard Kennedy School, toldThe Guardian. "Putting actual numbers to it in a credible way is tough."

Taylor himself is the author of a somewhat similar study that showed that pesticide use and infant mortality rose during years in which cicadas appeared; the insects do so at 13-17 year intervals.

David Rosner, a historian based at Columbia University, said the new bat study joins a large body of evidence dating back to the 1960s that links pesticide use with negative human health outcomes. "We're dumping these synthetic materials into our environment, not knowing anything about what their impacts are going to be," he said. "It's not surprising—it's just kind of shocking that we discover it every year."

Frank's claim about the cause of increased infant mortality should be taken with some caution, said Vermeulen, the Dutch researcher. He said the loss of agricultural income caused by bat die-offs could be connected to the increased deaths in complex ways.

The exact causal mechanism isn't known, Frank told media outlets, but the data shows the rise of infant mortality didn't come from food contamination by insecticides—rather, it's more likely it came via the water supply or contact with the chemicals.

Frank's other research extends beyond pesticide use. He and another researcher recently estimated that hundreds of thousands of human beings have died in India due to the collapse of the country's vulture population, as rotting meat increased the spread of diseases such as rabies.

Frank is not the first to study the impacts of white-nose syndrome on humans. Other studies have shown a reduction in land rents in counties hit by the bat plague and documented the billions of dollars that farmers have lost as their natural pest control disappeared.

The syndrome attacks bats while they hibernate. It was first identified in New York in 2006 and has since spread to much of North America. It's believed to have been brought over from Europe. It doesn't affect all bat species, but it's killed more than 90% of three key species, and bats also face a myriad of other threats, including habitat loss, climate change, and the dangerous churn of wind turbines.

Frank's bracing study should be a call to arms, experts said.

A number of progressives and left-leaning political figures this week suggested that presumptive Democratic presidential nominee Kamala Harris should choose Minnesota Gov. Tim Walz as her running mate.

Walz was the subject of a flurry of media attention over the last week, including glowing coverage in The Washington Post and The New York Times on Friday, as the Democrats ran an accelerated search for their vice presidential candidate.

While there hasn't been an organized progressive effort to push for Walz, he's regarded as the most friendly to left and working-class causes of the politicians known to be in the running, all of whom are white men. Progressives have expressed concerns over Pennsylvania Gov. Josh Shapiro, who's seen by many as the most likely choice.

"I want somebody who's really strongly pro-labor and understands labor, because this is a big part of the working-class agenda and making sure that we win working-class votes," Rep. Pramila Jayapal (D-Wash.), chair of the Congressional Progressive Caucus, said in explaining why she favored Walz, The Hill reported Friday.

Walz's appeal, buoyed by the sense that he's a straight-talking everyman, goes well beyond progressive circles. Born and raised in Nebraska, he served in the National Guard and worked as a high school teacher and coach. He served six terms as a Democrat in U.S. Congress, representing a rural area of Minnesota that borders Iowa. In 2016, he won reelection in a district that 2024 Republican nominee Donald Trump won handily.

In 2018, Walz successfully ran for governor, and was reelected in 2022—this time with Democrats in the majority in both houses of the state Legislature. (The state party is called the Democratic-Farmer-Labor Party.) They quickly turned the state into what NBC Newscalled "a laboratory in pushing progressive policy."

Under Walz's leadership, Minnesota became the fourth state in the country to provide free school lunches for all students. The state also set up a paid family and medical leave program and a tax credit for low-income Minnesotans. Walz also signed into law the strictest rules in the country on "forever chemicals" that endanger public health.

Walz and his Democratic allies banned spending on state and municipal elections by firms that were 5% or more foreign-owned—nearly every S&P 500 firm—and thereby reduced the pernicious effects of the Supreme Court's 2010 Citizens United ruling on the state's elections. They also established trans rights, secured fundamental abortion rights, and made it possible for undocumented people to get driver's licenses.

David M. Perry, a Minnesota-based journalist and historian, said in an MSNBCopinion piece this week that he was initially skeptical of Walz, figuring him to be a conservative Democrat who wouldn't push an ambitious agenda, but had changed his mind—"entirely Walz-pilled," as he put it. He applauded Walz for the many state-level legislative accomplishments, and cited only "questionable decisions" during the 2020 George Floyd uprisings in the governor's negative column.

Shawn Fain, president of the United Automobile Workers union, on Thursday toldThe Detroit News that he supported either Walz or Kentucky Gov. Andy Beshear to be the Democratic vice presidential nominee, citing their strong pro-labor records. Some groups have called for Fain himself to be the vice presidential nominee.

Rep. Jamaal Bowman (D-N.Y.), a progressive member of "the Squad," also voiced for support for Walz and Beshear in a social media post on Friday. Gun rights activist David Hogg has likewise been promoting Walz on social media.

The Wall Street Journal wrote about Walz's "folksy demeanor" on Thursday, while the Post on Friday asked, in a highly complimentary profile, if the Minnesota governor could go "from teaching history to being part of it."

Ezra Klein, a left-leaning podcast host at the Times, released a full-length interview with Walz on Friday titled "Is Tim Walz the Midwestern dad Democrats need?"

Klein's first question focused on a word Walz had used that helped catapult him to relative fame in the last week: "weird," which the governor had used to describe Trump and his running mate, Sen. JD Vance (R-Ohio).

The "weird" criticism of the Republican leaders went viral and was quickly picked up by Harris herself. Whether she will pick up the inventor of the attack onto her ticket remains to be seen. She secured the necessary votes to become the nominee on Friday and she's expected to announce her choice of running mate as early as Saturday.

A Texas-based company has developed vending machines that sell bullets and installed them at a handful of grocery stores in Texas, Oklahoma, and Alabama, with plans for expansion into other states, according to news reports this week.

The machines, produced by American Rounds, based in the Dallas area, use artificial intelligence to verify the age of buyers, who must be 21 to purchase the shotgun, rifle, and handgun bullets on offer.

There are few federal regulations on the sale of ammunition, and only a small number of states have their own tougher laws.

The vending machines are "likely to stoke controversy," Newsweekreported, while Gizmodocalled their spread a "questionable new trend." Social media users wrote that the idea of vending machines for bullets was "insane", "horrible," and "beyond sick."

"In some states, you can now walk into a grocery store and buy bullets from a vending machine as if you were ordering a candy bar or a soda," Gizmodo reported, though it explained that the process was "slightly more rigorous... than buying a Twix."

Nick Suplina, senior vice president for law and policy at Everytown for Gun Safety, expressed concern about the accessibility of the ammunition.

"In a country awash in guns and ammo, where guns are the leading cause of deaths for kids, we don't need to further normalize the sale and promotion of these products," Suplina toldThe Associated Press.

The introduction of the vending machine comes as gun-control advocates increase their efforts to defeat the gun lobby. There were more than 500 shootings nationwide over the 4th of July weekend, according to Moms Demand Action.

Though Walmart, a major ammunition retailer, has put some restrictions on sales in the last ten years, thanks to public pressure that followed mass shootings, bullets remain widely available in the U.S.

"In most of the country it's harder to buy Sudafed than it is to buy ammunition," according toThe Trace, which characterized federal law on ammunition sales as "next to nonexistent."

There were once stricter federal laws in place on ammunition sales but they were undone when Congress passed pro-gun legislation backed by the National Rifle Association in 1986.

One of the new vending machines was the source of controversy in Tuscaloosa, Alabama last week.

"I got some calls about ammunition being sold in grocery stores, vending machines," Tuscaloosa Councilor Kip Tyner said during a city council meeting on July 2, according toABC 33/40. "I mean, I thought it was a lie. I thought it was a joke, but it's not."

The vending machine in question was removed from a Fresh Value supermarket in Tuscaloosa the next day. The store manager said that the machine was removed due to lack of sales.

The American Rounds machines can currently be found at four locations in Oklahoma, one in Alabama, and one in Texas. The company has plans to install a machine in Buena Vista, Colorado, and already has more than 200 installation requests from stores in nine states, CEO Grant Magers told Newsweek. "And that number is growing daily," he said.

American Rounds' website says that "the future of ammo sales is here."

There are no limits to how much ammunition a customer can buy, other than the machine running out of stock, Newsweek reported. American Rounds is targeting small towns where ammunition might not be readily available. The machines are always set up inside of stores, Magers said.

The process of making the purchase, including the use of facial recognition software to check against the ID being used, can take one minute and a half, Magers told the AP.

Experts emphasized the escalating risks of climate-related disasters and their disproportionate impacts on low-income people on Monday following flooding in Brazil that has killed at least 150 people and displaced more than 600,000.

The floods that hit over recent days and weeks have knocked out bridges and the main airport in Porto Alegre, a port city in southern Brazil. More than 460 of the 497 municipalities in the southern state of Rio Grande do Sol have been affected, with more than 2 million people impacted, according to provisional government data.

"The situation is catastrophic," said Rachel Soeiro, Médecins Sans Frontières (MSF) medical coordinator in Brazil, who visited the area by helicopter. "We were able to view the towns from above and noticed that in some cases we couldn't even see the roofs of houses.”

More than two feet of rain has fallen so far this month, according Brazil's national weather service, inundating large areas.

"Whole towns and large, urban city centers are in some cases almost completely underwater," the BBCreported on Saturday.

Experts connected the extreme rainfall to climate change, which increases the likelihood of such weather events. Incidents of extreme flooding have increased "sharply" across the planet in the last two decades, according to a study in Nature Water released last year.

"In many ways, this is not a disaster of Brazil’s making. The whole planet is experiencing increasingly rapid climate changes due largely to the greenhouse gases produced by a handful of wealthy nations," Cristiane Fontes (Krika), executive director of World Resources Institute (WRI) Brasil, wrote in a commentary earlier this month in which she called the situation a "wake-up call for the world."

In recent weeks, flooding has also hit China, the United Arab Emirates, and Australia, and WRI's staff in Kenya are dealing with dam breaches from heavy rains, Fontes noted.

A Brazilian expert indicated that the flooding, catastrophic as it has been, should not come as a surprise.

"People on the streets here in Brazil, they've attributed this change to global climate change driven by the increase of fossil fuels," Paulo Artaxo, a physics professor at the University of Sao Paulo, and a member of the Intergovernmental Panel on Climate Change (IPCC), told the Canadian Broadcasting Corporation. He explained that was in line with IPCC projections showing that southern Brazil would face more extreme rainfall due to tropical and polar currents.

In Brazil, as elsewhere, climate impacts are not evenly distributed. MSF relief efforts are focused on the most vulnerable, including Indigenous communities, one of which had been isolated by rising waters and without help for 10 days before being reached by the humanitarian group.

"Assisting those who are most vulnerable is one of our main concerns in such situations," Soeiro said. "These people were already facing difficult situations before the flooding. But their needs have risen further and access to them has become more difficult."

Some wealthy people in Porto Alegre have choices such as escaping to a second home, but in "rundown towns" on the city's periphery, low-income people have no such options, according to CNN.

Brazilian left-wing President Luiz Inácio Lula da Silva has pledged to provide relief money to families that lost their homes. Brazil is one of most unequal countries in the world, according to World Bank data.