What Happens to the Gut Microbiome After Taking Antibiotics?

The development of antibiotics was a breakthrough in medicine. But while they can save lives, they have a dark side. Microbes resistant to the drugs were responsible for more than one million deaths in 2019, according to a study published earlier this year in The Lancet

Furthermore, a growing number of studies are finding that even a short course of antibiotics can alter the makeup of the bacterial species in the gut. These community changes can be profound, with some people’s microbiomes taxonomically resembling those of critically ill ICU patients after taking the drugs. And the microbes that survive the treatment tend to carry resistance genes, potentially enabling pathogens to acquire the means to evade our best pharmacological weapons.

Overall, Washington University School of Medicine in St. Louis pathologist microbiologist Gautam Dantas says that the findings are a warning that “taking antimicrobials is a gamble every single time you do it, even if it’s fully warranted.”

Probing healthy microbiomes 

One of the tricky aspects of studying the effects of antibiotics is that the gut microbiomes of patients prescribed them are “already in disarray for other reasons,” says Dantas, especially among people who have been hospitalized. In such cases, it may be difficult to separate the antibiotic’s effects on the microbiome from illness-related alterations. So researchers—including Dantas his colleague, infectious disease specialist Jennie Kwon—have been turning to healthy volunteers.

“A lot of people prescribe [antibiotics] thinking that there’s very little harm, especially if it’s just an oral pill for a couple of days,” says Kwon. “Our question was, is that true? When you give a healthy person a short course of antibiotics, does that cause any disruption to the gut microbiome?” 

The team recruited 20 healthy volunteers divided them into four groups, each of which received a different antibiotic or combination of antibiotics for five days. The drugs chosen—levofloxacin, azithromycin, cefpodoxime, a combination of azithromycin cefpodoxime—are often given to patients with community-acquired pneumonia, even though the condition is sometimes viral. Fecal samples were collected analyzed before, during, after the antibiotics course, with the last sample taken six months post-treatment. From these samples, the researchers charted how the taxonomic diversity of bacteria in the gut changed any fluctuations to the copy number of resistance genes. 

Antibiotic Perturbation of Gut Microbiomes in Healthy Volunteers

After taking antibiotics, the diversity of microbes in healthy volunteer’s guts decreases sharply.


Immediately after taking antibiotics, the total culturable species richness decreased, the team found. For most of the volunteers, these measures returned to baseline values after two months—but the species present remained changed, notes Winston Anthony, a PhD candidate at Washington University School of Medicine in St. Louis who coauthored the Cell Reports paper the team published last month announcing the results. This means antibiotics “are fundamentally restructuring the microbiome,” he says.

In three of the healthy volunteers, who were assigned to different treatment groups, the gut microbiome was especially perturbed. They continued to have reduced microbiome diversity even at the end of the six months. “Their gut microbiome became more similar to that of an ICU patient than of a healthy individual,” says Kwon. Still, she noted that they the other participants felt fine. 

W. Joost Wiersinga, an infectious disease specialist at the University of Amsterdam who has separately studied the effects of antibiotics in healthy people, tells The Scientist the new work “adds to the evidence that antibiotics can have major detrimental effects on the gut microbiome in healthy adults.” 

Indeed, in the 2018 study conducted by Wiersinga colleagues, healthy volunteers who took a one-week course of broad-spectrum antibiotics experienced a drop in gut microbiome diversity an overgrowth of Streptococcus Lactobacillus genera. Although these bacteria became less abundant over time the participants’ microbiome composition remained different from its initial state for the duration of the study, which was up to 31 months after taking antibiotics.

“Antibiotic scarring” may have lasting impact on resistance

In addition to inducing compositional changes to the microbiome, antibiotics seem to increase the prevalence of resistance genes. In Anthony et al.’s study, for three of the four antibiotics (all but levofloxacin), there were higher relative numbers of antibiotic resistance genes in the samples taken six months after treatment—a change the authors call “antibiotic scarring.” 

This long-term increase in resistance genes is a notable insight for Francisco Guarner, a digestive system researcher at the University Hospital Vall d’Hebron in Barcelona who was not involved in the study. He describes the gut microbiome as an ecosystem that is perturbed by antibiotics. “When you take antibiotics, some bacteria in the network disappear [and] the others overgrow, so the balance is different. In this new balance, what you gain are bacteria that are more resistant to antibiotics.” 

Gut bacteria that harbor antibiotic resistance genes may pose several threats. When gut bacteria pathogens mingle, the resistance genes can be transferred, allowing pathogens to acquire resistance. One recently published study observed that resistant gut commensals can even degrade antibiotics in the gut, shielding pathogens from the effects of the drugs. 

See “How the Microbiome Influences Drug Action”

In further research, Kwon is investigating whether some healthy people in the community may serve as reservoirs for resistance genes, which could potentially be passed to others. 

Why do some people’s microbiomes respond differently to antibiotics?

It’s not yet clear why some people’s gut microbes seem to be especially disrupted by antibiotics. “There is a lot of variation between individuals,” Wiersinga notes, in whether people’s microbiomes recover to their initial states, if so, how long that takes.

Lack of Gut Microbiome Recovery after Antibiotics in Some Healthy Volunteers

graph depicting persistent reduction in gut microbe diversity for some antibiotics takers

For some putatively healthy volunteers, the diversity of gut microbes recovers much more slowly, if it recovers at all.


The state of the microbiome before treatment may play a factor in that, Anthony notes. In his study with Dantas Kwon, the three volunteers whose gut microbiomes came to resemble those of ICU patients started out with slightly lower species diversity. Anthony puts forward several hypotheses to explain this initial difference, including that they may have had rounds of antibiotics before the study. Discerning the cause of differential responses to antibiotics could help refine their use, Kwon says, though future studies will need to uncover the microbial metabolomic factors involved determine whether they have predictive clinical value.  

Ultimately, Wiersinga sees the accumulating findings as a reminder for doctors to “think twice when we prescribe antibiotics: does my patient really need it?” 

Like this article? You might also enjoy our bimonthly Microbiology Research Area Newsletter, which is filled with stories like this one. You can sign up for it here!

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They Thought the Skulls Were Murder Victims. They Were Off by Centuries.

In 2012, the authorities in the southern Mexican state of Chiapas entered a dark cave confronted a ghastly site: about 150 skulls sprawled across the ground, all with missing teeth shattered bits of bone.

The police started an investigation, believing it was a crime scene of migrants killed near the border with Guatemala, where gang violence is commonplace.

Indeed, it was a crime scene. Just not one that occurred recently.

Last week, 10 years after the discovery, the authorities said in a statement that they had determined the skulls were from sacrificial killings between A.D. 900 1200.

“We have already learned a lot of information,” Javier Montes de Paz, an archaeologist who analyzed the bones, said in a news conference on April 11. “But it’s also important to note: What were those craniums doing in that cave?”

Researchers at the National Institute of Anthropology History analyzed marks on the bones determined that the deaths had happened centuries ago. Such marks would appear only after “a lot, a lot of time” had passed, Mr. Montes de Paz said.

The researchers found that the victims had been beheaded, that most of the bones were from female victims, that all were missing teeth, though it was unclear if they had been extracted before or after death, Mr. Montes de Paz said.

The researchers also found the skeletal remains of three infants.

The pre-Hispanic bone pile in the Comalapa cave was likely a tzompantli — an altar for worshiping gods that would look like a modern-day trophy rack, with skulls placed on aligned wooden sticks, Mr. Montes de Paz said. Similar practices were common in Maya, Aztec other Mesoamerican civilizations, according to Smithsonian Magazine.

The wooden material “disappeared over time could have collapsed the skulls,” Mr. Montes de Paz added.

Investigators in the cave also found aligned wooden sticks, another sign of a tzompantli, according to a statement from the National Institute of Anthropology History.

While the researchers have yet to conclude their study, Mr. Montes de Paz said it was most likely that several Mesoamerican communities used the cave. Its two entrances were so steep that researchers had to use a ladder to enter.

It was unclear how the skulls were found a decade ago, or by whom. The authorities said in a statement that a “complaint” had alerted them to the discovery in the town of Carrizal, in the municipality of Frontera Comalapa. The National Institute of Anthropology History did not respond to emailed questions on Wednesday.

Anthropologists studying the skulls found other bone fragments at the site, including a femur pieces from arms. Intact bodies, however, had not been found, Mr. Montes de Paz said.

The Spanish invasion occurred in the 1500s. According to Smithsonian Magazine, when the Spanish arrived, they were scared of the rituals.

But the sacrifices appeared to have been common in Chiapas. The National Institute of Anthropology History said that in the 1980s, anthropologists explored Cueva de las Banquetas, a cave, found 124 skulls that did not have teeth. In 1993, Mexican French explorers in Ocozocoautla traveled to Cueva Tapesco del Diablo, another cave with five skulls inside.

Mr. Montes de Paz said his team was eager to further explore the Comalapa cave soon.

If people visit such sites in the future see skulls, he said, they should not “touch or pick up anything.” Otherwise, they could affect the archaeological integrity of the site. The people who found the skulls in Chiapas in 2012 accidentally touched some of the bones, he said. “You affect the history,” he said. “And a lot of information is lost.”

Still, he believed that after more analysis, the story of the skulls could soon be fully told.

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La pandemia ha sido dura con nuestros pies

En marzo de 2020, Krista Fahs, de 53 años, comenzó a trabajar desde casa. Debido a que pasaba el día sentada en su escritorio, la vendedora que trabaja para un distribuidor de computadoras se olvidó de los tenis que usaba a diario. De repente se dio de cuenta de que lavaba la ropa, jugaba con su gato e incluso iba a visitar a los vecinos sin haberse puesto los zapatos. “Andaba descalza todo el tiempo”, dijo.

Luego de pasar unos meses trabajando desde casa, comenzó a sentir una punzada de dolor en el talón, pero lo ignoró hasta el mes pasado, cuando se hizo demasiado intenso como para pasarlo por alto. Incluso cuando estaba en la cama, el dolor no cesaba. “‘Esto es ridículo’”, recordó haber pensado. “Ni siquiera sabía cómo iba a dormir por el dolor”.

El comienzo de la pandemia coincidió con un descenso considerable de los traumatismos en los pies, afirmó Robert K. Lee, jefe de cirugía podológica de pies y tobillos del Centro Médico de Santa Mónica de la Universidad de California, campus Los Ángeles, pero su consultorio no tardó en repoblarse con pacientes como Fahs que se quejaban de dolor en los pies. “Me dije: ‘Ajá, así que este es el efecto de la pandemia en los pies de todo el país’”, comentó.

No hay datos concretos sobre el aumento del dolor de pies, pero James Christina, director ejecutivo de la Asociación Médica Estadounidense de Podología, dijo que ha sido una tendencia evidente para muchos de los 12.000 miembros de esa organización.

Rock Positano, codirector del Servicio No Quirúrgico de Pie y Tobillo del Hospital de Cirugía Especial de Nueva York, ha registrado un incremento tan notable del dolor de pies —entre un 20 y un 30 por ciento— que definió ese fenómeno como “pie pandémico”.

Ahora que ha llegado la primavera, las regulaciones se flexibilizan y la gente está ansiosa por recuperar su cuerpo y sus aficiones anteriores a la pandemia, por lo que salen a la calle, afirma James Hanna, podólogo y presidente de la Asociación Médica de Podología del Estado de Nueva York. Muchos están agravando las lesiones de los pies existentes o creando otras nuevas.

“Las personas pensaban que podían retomar las cosas o hacer algo que no habían hecho durante estos dos años”, dijo, “pero sus pies no están preparados para lo que sus cuerpos quieren hacer”.

Al instituir un par de medidas sencillas, Hanna les asegura a quienes les aquejan sus pies que ese dolor puede ser aliviado, además de prevenido.

Algunas de las dolencias más comunes de los pies se producen simplemente porque el pie estuvo sujeto a un esfuerzo mayor durante la pandemia. Quizá hayas optado por caminar largas distancias en vez de utilizar el transporte público o hayas pasado mucho tiempo descalzo en casa. “La gente no se da cuenta de la cantidad de kilómetros que recorre al caminar y estar de pie en sus casas”, dijo Positano.

A Fahs se le diagnosticó una de esas lesiones por sobreuso, la fascitis plantar, en la que el ligamento bajo el pie que sostiene el arco se inflama, lo que a menudo se siente como un dolor en el talón. “Sabía qué era porque mi hermano, mi hermana y una de mis mejores amigas también la sufrieron recientemente”, explica.

La metatarsalgia es otra lesión por uso excesivo, causada igualmente por la inflamación, pero en las articulaciones de los dedos, lo que provoca dolores en la almohadilla del pie.

Para los que empiezan con rutinas de atletismo ambiciosas apenas saliendo de la pandemia, la tendinitis de Aquiles ha sido un diagnóstico común. El tendón conecta el músculo de la pantorrilla con el hueso del talón y, con un aumento repentino del uso, puede irritarse e hincharse.

Estas heridas no solo afecta la salud de los pies. Si no se tratan, pueden “ir subiendo” y causan dolor de rodillas, cadera y espalda. “La gente cree que se están cayendo a pedazos, pero no”, dijo Positano. “Están usando sus pies de más”.

Las lesiones por uso excesivo no son las únicas razones por las que la gente siente dolor de pies últimamente. Priya Parthasarathy, cirujana podológica de Maryland, también ha observado un aumento de las fracturas de dedos y pies. Algunas son causadas, afirmó, por patear accidentalmente los muebles —resultado de estar en casa y descalzo más a menudo— y por tropezar y caer encima de las mascotas. “Ves una, luego ves dos, luego tres y luego cuatro”, comentó sobre esas fracturas relacionadas con las mascotas, “y te dices: ‘Espera, definitivamente hay una conexión aquí’”.

Mientras tanto, Judith F. Baumhauer, cirujana ortopédica del Centro Médico de la Universidad de Rochester, ha tenido que eliminar más juanetes, que son protuberancias huesudas en la base del dedo gordo. Sin un calzado apropiado, el pie a veces se extiende —en realidad se ensancha— y las estructuras anatómicas podrían cambiar. Entre otros problemas, esto además puede agravar los juanetes.

“Dejan que sus pies hagan lo que quieran”, dice Baumhauer, “y ahora que tienen que volver al trabajo, los pies se rebelan”.

Baumhauer señaló que el aumento de peso pandémico también podría ser el culpable del incremento de las molestias en los pies. Explicó que incluso un par de kilogramos de más tienen un impacto. “Es, literalmente, cuestión de física”, sostuvo, explicando que el pie soporta cuatro veces la fuerza de nuestro peso corporal al caminar. Perder o ganar 2,5 kilogramos supondría un cambio de “nueve kilogramos en el tobillo y el pie”, dijo.

Jacquelyn M. Dylla, profesora asociada de Fisioterapia Clínica en la Universidad del Sur de California, afirma que uno de los principales desencadenantes es que la gente haga demasiadas cosas demasiado rápido. Muchos, sin darnos cuenta, hemos sufrido atrofia y pérdida de densidad ósea por la inactividad, lo que hace más difícil estabilizarnos en superficies irregulares. “Las lesiones más pequeñas están causando problemas más catastróficos”, indicó. “Tengo pacientes que parece que estuvieron en un accidente automovilístico”, añadió, “pero solo se torcieron el tobillo en una excursión”.

Incluso los niños pequeños, después de uno o dos años de escuela virtual, experimentan problemas cuando se incorporan de lleno al deporte. “Tienes a un niño sentado en casa todos los días durante un año que va directo a hacer campo traviesa”, comentó Parthasarathy.

Los podólogos dicen que una de las soluciones para el dolor de pies puede ser bastante sencilla: usar calzado con soporte. Eso significa una suela semirrígida, una puntera amplia y una pequeña elevación del talón. Ve a que te tomen bien las medidas en una zapatería y, si no quieres usar zapatos de calle en tu casa, adquiere un par específico para uso en interiores. Si utilizas un calzado más viejo, asegúrate de que la suela no esté demasiado desgastada, ya que puede haberse degradado demasiado como para ofrecer un apoyo sustancial. También se pueden añadir plantillas para dar mayor soporte al arco del pie.

Según Dylla también es esencial preparar nuestro cuerpo para una actividad nueva fortaleciéndolo primero. Esto significa ejercitar los pies con ejercicios de flexión de los dedos y del arco. “Hay abdominales para fortalecer los músculos del vientre”, dijo Dylla, “flexionar el arco es el equivalente”.

En opinión de Hanna, el mejor consejo quizá sea empezar despacio. “Si vas a empezar a hacer senderismo, hazlo a un ritmo moderado en una distancia corta”, aconsejó. “Si lo toleras bien, tal vez puedas ir a un ritmo más rápido en distancias más largas”.

Si tienes algún dolor de pies persistente, consulta a un podólogo. Hay muchas formas sencillas para que los médicos alivien el dolor y así prevenir la aparición de problemas crónicos. Si tienes molestias, “busca atención médica”, apuntó Baumhauer, “porque tenemos muchos trucos bajo la manga”.

Los podólogos también dicen que los estiramientos son cruciales para prevenir y tratar el malestar en los pies. “Un calentamiento adecuado”, dijo Hanna, “no puedo enfatizar esto lo suficiente”.

Por la mañana, incluso antes de ir al baño, Hanna recomienda flexionar los pies tirando de los dedos hacia el cuerpo. A continuación, imagina que tus dedos son un lápiz y escribe el alfabeto. “Si haces eso, activarás todas las articulaciones y será mucho menos probable que te lesiones”.

Aunque la pantorrilla parece alejada de la planta del pie, su estiramiento desempeña un papel esencial para caminar sin dolor. “Cuando la pantorrilla y el tendón de Aquiles están tensos”, dice Lee, “se crea mucha más tensión en todas las articulaciones del pie”.

Sugiere ponerse en posición de embestida con un pie delante del otro, las manos apoyadas en una pared y los pies apoyados en el suelo. Debes sentir el estiramiento en la pantorrilla de la pierna de atrás. Sugiere hacer esto varias veces a lo largo del día.

Masajear la zona del arco del pie también puede prevenir lesiones al mantener la planta del pie ágil. Lee aconseja coger una pelota de tenis o de golf mientras se está sentado en un escritorio o mientras se ve la televisión. “Haz rodar el pie sobre la pelota y masajea esa zona para aflojar esas fibras”, dice.

Sin embargo, si tienes dolor en el talón, acude a un médico para que te revise el pie antes de realizar los estiramientos. En algunos casos, dijo Positano, puede haber desgarros no diagnosticados en la fascia plantar que el estiramiento puede empeorar.

Si tienes algún dolor de pies persistente, reserva una cita con un podólogo. Hay muchas formas sencillas en que los médicos pueden aliviar el dolor y prevenir la aparición de problemas crónicos. Si tienes molestias, “busca atención”, dijo Baumhauer, “porque tenemos muchos trucos bajo la manga”.

Mara Altman es periodista y autora de Gross Anatomy: Dispatches From the Front (Back).

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Climate Change Makes It Harder to Fight Fires With Controlled Burns

Summer is still more than a month a half away, but enormous wildfires have already consumed landscapes darkened skies in Arizona, New Mexico Nebraska. Whipping winds threw flames across the terrain around Boulder, Colo., in December March.

In Boulder, worries about wildfire used to be focused around August late summer, when lightning strikes can ignite the timbers. “Now the focus is every month,” said John Potter, a deputy director at the city’s Open Space Mountain Parks department.

As deadly wildfires become a terrifying fixture of life for many Americans, more of the country is embracing an ancient tool to limit the devastation: careful, controlled burns that clear away vegetation help prevent wildfires from exploding into catastrophes. But in many places, the changing climate is making intentional burns much more complicated to carry out.

The United States Forest Service used prescribed fire across a record 1.8 million acres of federal llast year, the agency is aiming to treat an additional 50 million acres with fire mechanical brush thinning over the coming decade. President Biden’s infrastructure law puts $5 billion toward reducing combustible flora combating wildfires in other ways. California, Oregon other states are exploring legal changes to encourage more burning.

With human-caused global warming heating up drying out large parts of the country, however, wildfire seasons are growing longer, narrowing the windows for performing controlled fires safely. Shifting patterns of rain wind are adding to the complications for burners. In many states, efforts to treat more lwith fire are also running up against bureaucratic hurdles funding personnel shortages.

So far this spring, exceptionally dry windy conditions have prevented Boulder’s mountain parks department from carrying out any major burns, Mr. Potter said. That raises plenty of concern about how bad wildfires could get this summer.

“Fingers crossed,” he said.

Even in humid Florida, changing conditions are forcing lmanagers to get creative about when they burn, said J. Morgan Varner, the director of fire research at Tall Timbers Research Station LConservancy in Tallahassee. Heavy rains derailed plans in March, which is usually prime season for burning in the state. “We’re dealing with a really dynamic climate that makes planning difficult,” Dr. Varner said.

For much of the past century, America’s approach to fires was to put out any all of them. A series of devastating blazes in 1910 hardened the government’s belief that fire was the enemy. Indigenous land-management practices were cast aside as pseudoscience; intentional burning was regarded as the behavior of woods arsonists miscreants.

But the ferocious infernos of recent years have called attention to the need for a better way. Scientists now believe the long focus on fire suppression left the nation’s forests overcrowded overgrown — one reason today’s wildfires are so destructive.

Between 2005 2019, major blazes in the West the Great Plains burned nearly four times as much total area each year, took place nearly twice as often, compared with the last two decades of the 20th century, one recent study found. Since 1979, nearly every part of the globe where wildfires are a problem has experienced more extreme heat dryness, other recent research has shown.

In California, the winter rainy season is getting shorter but more intense, scientists say. This gives grass brush more time to dry out turn flammable in the fall, while still providing them ample water to grow the following spring — a double whammy for wildfire risk.

“I don’t think people realize that we’re actually at a point where, some of these fires, we cannot put them out,” said Lenya N. Quinn-Davidson, a fire adviser with the University of California Cooperative Extension director of the Northern California Prescribed Fire Council. “We really need to be thinking in different ways about how we do things.”

Changes are afoot in some states. California passed a law last year letting lmanagers off the hook for firefighting costs in the unlikely event that a properly planned prescribed fire goes awry. Oregon is looking to do something similar. The California legislature is considering creating a $20 million fund that would compensate homeowners for losses caused by prescribed burns.

Oregon in 2019 changed its air quality rules to allow more prescribed fires to take place near towns communities. Mr. Potter said Boulder’s mountain parks department was exploring whether it needed to work with Colorado officials to re-examine air quality strictures. The trade-off, of course, might be more smoke choking residents’ lungs.

“There’s still sometimes that lack of understanding that a little smoke right now can save us from a whole lot of smoke later on,” said Jessica E. Halofsky, director of the Forest Service’s Northwest Climate Hub in Olympia, Wash.

Only a tiny share of prescribed fires get out of control cause injuries or damage to homes. But when they do, they can leave long-lasting distrust.

In Bastrop County, Texas, heavy gusts whipped a prescribed fire in January into a blaze that took nearly a week to contain. An independent investigation later found that, while conditions that day technically met the standards for a safe burn, the state had failed to have enough staff on site a bulldozer for contingencies.

The incident stoked memories of a wildfire that ripped through the same area in 2011, destroying 1,600 homes killing several people.

“The folks that are still here from 2011, they’re always nervous,” said Roxanne Hernandez, a Bastrop County resident. After the 2011 blaze, Ms. Hernandez completed a training program in prescribed fire started carrying out burns on her 53-acre ranch. But for other residents, she said, “it’s back to Smokey the Bear: ‘Put it out!’ And that’s not the answer.”

Crews managers trained in prescribed fire are in short supply in many places, foresters say. Many of the same people are also called upon to help extinguish wildfires.

“As the wildfire seasons get longer, those folks are gone for longer,” said Dan Porter, the forest program director in California at The Nature Conservancy, an environmental nonprofit. “When they come back, we may say, ‘Hey, would you like to go do a prescribed fire?’ Well, they’ve been out cutting line for four months breathing smoke for four months. They need to go see their family take a break.”

Ms. Quinn-Davidson of the University of California Cooperative Extension has hosted courses as part of a new program to train more people to lead prescribed fires in their communities. But with so many of California’s catastrophic wildfires taking place on federal land, only bigger policy changes large-scale prescribed fire projects can stop further harm to the broader landscape, she said.

Last summer, the Forest Service’s chief, Randy Moore, restricted the use of prescribed fire on agency lands to make sure resources were available to fight wildfires. He also ordered a pause on allowing backcountry fires to burn if they provided ecological benefits didn’t threaten homes or infrastructure.

The halt was temporary, but it was enough to make some ecologists fear that officials’ recent championing of fire could still go into reverse. If the goal is to return the lto an older ecological state, one in which frequent natural fires kept forests vibrant resilient, then the scale of the task is staggering.

California is aiming to use prescribed fire on 300,000 acres of lannually by 2025. Far more of the state burned each year in centuries past, before intensive modern settlements transformed the landscape, scientists have estimated. Smoke haze fouled the skies through much of summer fall.

It may not be practical or desirable to go back to that world in its entirety. Still, as more human activity spreads into onetime wilderness, societies will have to learn to accept fire in one form or another, said Heath D. Starns, a fire researcher at Texas A&M University president of the Prescribed Burn Alliance of Texas.

“It’s a process that really needs to occur, ecologically,” Dr. Starns said. “And our best option is to live with it, but to determine when, where under what conditions fires happen.”

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Humans Were Actually Apex Predators For 2 Million Years, Evidence Shows

Paleolithic cuisine was anything but lean green, according to a 2021 study on the diets of our Pleistocene ancestors. For a good 2 million years, Homo sapiens their ancestors ditched the salad dined heavily on meat, putting them at the top of the food chain.


It’s not quite the balanced diet of berries, grains, steak we might picture when we think of ‘paleo’ food. But according to anthropologists from Israel’s Tel Aviv University the University of Minho in Portugal, modern hunter-gatherers have given us the wrong impression of what we once ate.

“This comparison is futile, however, because 2 million years ago hunter-gatherer societies could hunt consume elephants other large animals – while today’s hunter gatherers do not have access to such bounty,” said Miki Ben‐Dor from Israel’s Tel Aviv University in April last year.

A look through hundreds of previous studies on everything from modern human anatomy physiology to measures of the isotopes inside ancient human bones teeth suggests we were primarily apex predators until roughly 12,000 years ago.

Reconstructing the grocery list of hominids who lived as far back as 2.5 million years ago is made all that much more difficult by the fact plant remains don’t preserve as easily as animal bones, teeth, shells.

Other studies have used chemical analysis of bones tooth enamel to find localized examples of diets heavy in plant material. But extrapolating this to humanity as a whole isn’t so straight-forward.


We can find ample evidence of game-hunting in the fossil record, but to determine what we gathered, anthropologists have traditionally turned to modern-day ethnography based on the assumption that little has changed.

According to Ben-Dor his colleagues, this is a huge mistake.

“The entire ecosystem has changed, conditions cannot be compared,” said Ben‐Dor.

The Pleistocene epoch was a defining time in Earth’s history for us humans. By the end of it, we were marching our way into the far corners of the globe, outliving every other hominid on our branch of the family tree.

(Miki Ben Dor)

Above: Graph showing where Homo sapiens sat on the spectrum of carnivore to herbivore during the Pleistocene Upper Pleistocene (UP).

Dominated by the last great ice age, most of what is today Europe North America was regularly buried under thick glaciers.

With so much water locked up as ice, ecosystems around the world were vastly different to what we see today. Large beasts roamed the landscape, including mammoths, mastodons, giant sloths – in far greater numbers than we see today.


Of course it’s no secret that Homo sapiens used their ingenuity uncanny endurance to hunt down these massive meal-tickets. But the frequency with which they preyed on these herbivores hasn’t been so easy to figure out.

Rather than rely solely on the fossil record, or make tenuous comparisons with pre-agricultural cultures, the researchers turned to the evidence embedded in our own bodies compared it with our closest cousins.

“We decided to use other methods to reconstruct the diet of stone-age humans: to examine the memory preserved in our own bodies, our metabolism, genetics physical build,” said Ben‐Dor.

“Human behavior changes rapidly, but evolution is slow. The body remembers.”

For example, compared with other primates, our bodies need more energy per unit of body mass. Especially when it comes to our energy-hungry brains. Our social time, such as when it comes to raising children, also limits the amount of time we can spend looking for food.

We have higher fat reserves, can make use of them by rapidly turning fats into ketones when the need arises. Unlike other omnivores, where fat cells are few but large, ours are small numerous, echoing those of a predator.


Our digestive systems are also suspiciously like that of animals higher up the food chain. Having unusually strong stomach acid is just the thing we might need for breaking down proteins killing harmful bacteria you’d expect to find on a week-old mammoth chop.

Even our genomes point to a heavier reliance on a meat-rich diet than a sugar-rich one.

“For example, geneticists have concluded that areas of the human genome were closed off to enable a fat-rich diet, while in chimpanzees, areas of the genome were opened to enable a sugar-rich diet,” said Ben‐Dor.

The team’s argument is extensive, touching upon evidence in tool use, signs of trace elements nitrogen isotopes in Paleolithic remains, dental wear.

It all tells a story where our genus’ trophic level – Homo’s position in the food web – became highly carnivorous for us our cousins, Homo erectus, roughly 2.5 million years ago, remained that way until the upper Paleolithic around 11,700 years ago.

From there, studies on modern hunter-gatherer communities become a little more useful, as a decline in populations of large animals fragmentation of cultures around the world saw to more plant consumption, culminating in the Neolithic revolution of farming agriculture.

None of this is to say we ought to eat more meat. Our evolutionary past isn’t an instruction guide on human health, as the researchers emphasize, our world isn’t what it used to be.

But knowing where our ancestors sat in the food web has a big impact on understanding everything from our own health physiology, to our influence over the environment in times gone by.

This research was published in the American Journal of Physical Anthropology.

An earlier version of this article was published in April 2021.


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