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The Dirty Secret About How Our Hands Spread Disease

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Tuesday, March 12, 2024

Sabrina Sholts Curator, Anthropology, National Museum of Natural History “There is no act of life so dangerous to others,” fumed physician Robert Eccles in 1909, “as carelessness concerning the condition of our hands.” He really meant it. In a seven-page rant titled “Dirty Hands,” published in the Dietetic and Hygienic Gazette of New York City, Eccles blamed filthy fingers for the deadliest crimes of the age. Causing more deaths than “bullets, poisons, railway accidents and earthquakes combined,” the human hand was a weapon of mass destruction that extinguished innocent lives by the hour, according to this Brooklyn-based doctor. And Eccles was fighting back. With ample ammunition from research in bacteriology, a field in its heyday by the close of the 19th century, he had scientific proof that uncleanliness could transform hands into petri dishes of pathogens. “Until the HABIT is established of purifying the hands, both timely and properly, no lessening of this human misery seems possible under existing conditions,” Eccles declared. The main target of the doctor’s ire was a private cook named Mary Mallon, the notorious “Typhoid Mary” of medical lore, who was serving a sentence of forced isolation on North Brother Island in New York City’s East River. Mallon was arrested as a public health threat in 1907 after being identified as the source of seven household outbreaks of typhoid fever since 1900. Epidemiological evidence suggested that she infected her clients by preparing their meals with unclean hands—a charge that Mallon rejected. She didn’t deny her poor hand hygiene but also failed to see how she could have infected anyone. Typhoid fever has many symptoms, such as a prolonged high fever, headache and malaise, and Mallon had none of them. The disease is caused by the bacterium Salmonella typhi, which was well-described and identifiable with diagnostic tests by the 1890s. Untreated typhoid fever can be fatal in up to 30 percent of cases, and before the advent of antibiotics, it caused thousands of deaths in the United States each year. Only humans are infected by and transmit the pathogen, usually through food and water contaminated with Salmonella-filled urine or feces. This is likely how Mallon spread the disease given that laboratory analyses of her feces showed pathogens aplenty, which suggested that none of her trips from the bathroom to the kitchen involved soap. Vilified as “Typhoid Mary” by the press, Mary Mallon was arrested as a public health threat in 1907. Fotosearch / Stringer via Getty Images Mallon refused to believe that she was an asymptomatic carrier of typhoid fever, even after her release in 1910. She continued to cook, but she didn’t adopt the hand-washing habit that Eccles preached. Thus he was probably pleased by the further punishment that she faced for her dirty hands when health authorities tracked her down again. After more people had fallen ill and died from her contaminated cuisine, she was arrested and isolated for a second time in 1915, with a sentence that lasted the rest of her life. The story of Mallon holds many lessons, and the danger of unclean hands is one of them. But still today, disease risks frequently involve pathogens and routes of transmission that we fail to recognize. I recall when virologist Matt Frieman made this point effectively at a workshop in 2017. The scientists in attendance were invited to present and discuss their research with a group of filmmakers, and Matt’s topic was perfect for a Hollywood movie: deadly viruses that have recently emerged in humans. When Matt finished his presentation, one filmmaker asked him how much we needed to worry about these pathogens at present. You could hear the alarm in her voice. And without missing a beat, Matt replied, “Right now, our most immediate threat is a norovirus outbreak from that jar of cookies by the bathrooms.” He was right. In our meeting venue, arranged by one of the premier scientific organizations in the United States, there was an inviting jar of chocolate chip cookies on a small table … directly on the path to and from the toilets. Like Salmonella typhi, norovirus is an intestinal pathogen that’s commonly spread through contaminated food, water and surfaces. It’s one of the world’s leading causes of gastroenteritis (also known as stomach flu) and extremely contagious, partly because a small dose can cause infection. Incredibly, a sick person can shed billions of tiny particles of norovirus in their stool and vomit, and it takes as few as 18 of those particles to infect another person. Norovirus is also highly transmissible because it’s picked up and left all over the place by our grabby hands. For an example, look to the utterly miserable weekend of an Oregon girls soccer team in 2010. While sharing hotel rooms at an out-of-state tournament, several of the team’s members fell ill with acute gastroenteritis. The first girl to become sick—called the index patient—had used a bathroom where a grocery bag of snacks was being stored. She didn’t actually touch the bag or its contents but instead contaminated their surfaces by vomiting, excreting diarrhea and flushing the toilet—all of which can aerosolize noroviruses, thereby making them airborne. The index patient went home the next morning, but cookies, chips and fresh grapes in the grocery bag were passed around at the team’s lunch that afternoon. Within 48 hours, seven other players and chaperones became sick, too. Sickness is often a helpful signal of infection. It tells the patient, as well as the rest of us, to steer clear. But like Salmonella typhi, norovirus infections can be contagious without any symptoms at all. People can shed the virus in their feces before they start to feel sick or for weeks after they begin to feel better. Hand washing is therefore one of the simplest and most effective ways to prevent transmission. Placing treats far away from the restrooms is another one. How our hands work Our hands wouldn’t work so well as disease vectors if we didn’t use them so much. And we wouldn’t use them so much if there weren’t so much that they can do. So before we delve further into a discussion of how humans give a helping hand to pathogens in their transmission, let’s consider what makes our hands so helpful in the first place. Put one hand flat on a surface, palm down, and you might be able to make out the contours of 14 short bones called phalanges in your thumb and fingers, in addition to five longer ones in your palm called metacarpals that articulate with your wrist. Eight small wrist bones called carpals are mostly hidden from external view. Some of them are surprisingly charismatic in shape, resembling miniature forms of common objects that range from a boot to a boat. But there’s nothing cute about what they do. These 27 bones give each hand its rigid, knuckled structure, while joined and surrounded with muscles, tendons, ligaments, blood vessels and nerves that connect with other elements of the body and carry out directions from the brain. Together they’re critical components of the anatomical architecture that allows your hand to move. At each of your fingertips there’s an ever-growing, translucent plate of fibrous protein called keratin, otherwise known as a nail. Although they’re nice for decoration, your nails protect and enhance your sensitivity to touch, too. Flip your hand over, and you can better understand how. The nails provide a hard backing for fibrofatty cushions of flesh at each of your fingertips, five fingertip pads in addition to several palm pads on the underside of each hand. Extremely creased and furrowed, these pulpy little pillows of nerve endings have some of the highest concentrations of receptors in all the skin, making them highly sensitive to sensory stimuli. Try them out with a tap or two—but be careful! Fingertip injuries are potentially debilitating and common, particularly in curious young children who use their hands to explore their environment without realizing the physical dangers involved. Even beyond childhood, through touch sensations and tactile perceptions of temperature, texture and vibration transmitted to the brain, fingers are essential to how most people contact and interact with the external world throughout life. Human hands have some minor distinctions among primates that make a big difference. The human hand can be distinguished from those of other living apes by a high thumb-to-digit ratio, meaning that we have a relatively long thumb when measured against the fingers on the same hand. One major advantage of these hand proportions is that our thumb can be placed squarely in pad-to-pad contact with, or positioned diametrically opposite to, any or all of our fingers. Thumb opposition isn’t unique to humans, and in fact an opposable thumb facilitates the enhanced grasping abilities of many primates. But what sets our thumb apart is its power. Modern humans have a unique combination and greater number of forearm muscles versus other primates, as well as a notable musculature in the thumb. Altogether, these features allow humans to firmly and precisely grip objects for certain types of manipulation that other animals, even our living primate relatives, can’t achieve. Imagine pinching a piece of paper between your thumb and index finger, for example. We use this type of forceful, pad-to-pad precision gripping without thinking about it, and literally in a snap. Yet it was a breakthrough in human evolution. Other primates exhibit some kinds of precision grips in the handling and use of objects, but not with the kind of efficient opposition that our hand anatomy allows. In a single hand, humans can easily hold and manipulate objects, even small and delicate ones, while adjusting our fingers to their shape and reorienting them with displacements of our fingertip pads. Our relatively long, powerful thumb and other anatomical attributes, including our flat nails (which nearly all primates possess), make this possible. Just picture trying—and failing—to dog-ear a page in a book with pointy, curved claws. With a unique combination of traits, the human hand shaped history. No question, stone tools couldn’t have become a keystone of human technology and subsistence without hands that could do the job, along with a nervous system that could regulate and coordinate the necessary signals. Even for those who have never attempted to make a spear tip or arrowhead from a rock (which is most of you), it’s obvious that it would require strong grips, constant rotation and repositioning, and forceful, careful strikes with another hard object. And even for those who have done so, it can be a bloody business. A journey through history and around the globe to examine how and why pandemics are an inescapable threat of our own making. But our manual dexterity isn’t determined by our hand anatomy alone. Our nervous system, which involves the brain, spinal cord and a complex system of nerves, exerts control over our hand movements. Indeed, neurological factors may partly explain why primate species with similar hands can differ quite a bit in their mechanical abilities. For example, the tufted capuchin and common squirrel monkey both have pseudo-opposable thumbs, but only the capuchin displays relatively independent finger movements and precision gripping in picking up small objects and manipulating tools. Functional differences in their neuroanatomy may be the cause. Of course, the most common object that people touch nowadays is a screen. And the tap-tap-tap movements of our fingers is a unique human ability, as no other primate can move their fingers as rapidly and independently as we do. Here again, we can thank the extraordinary human brain given that normal finger tapping requires the functional integrity of different parts of our central nervous system. Moreover, repetitive rapid finger tapping is a common test of fine motor control of the upper extremities as well as a standard means of assessing the potential effects of neurodegenerative disease and traumatic brain injury. While a human can turn the page of a book using forceful thumb-finger opposition, other apes can’t form this pad-to-pad “precision grip” due to the relative shortness of the thumb compared to the other fingers, as seen in the left hand of this chimpanzee. Instead, this chimpanzee is gripping the pages of a magazine by holding them between the knuckles of its right hand. Mertie . via Flickr under CC By-SA 2.0 Deed Our use of information technology, like smartphones and computers, is often described as having the world at our fingertips. But this metaphor makes sense when it comes to microbes, too. Microbes and our hands The vast majority of microbes on and in the human body are persistent but harmless colonists. Those on the hand are no exception. Many of the microbes at our fingertips provide important benefits for human health. For instance, one of the key functions of the skin microbiota, which are mostly bacteria, is acid resistance. By regulating the acidity of the skin, these microbes help to maintain a powerful permeability barrier that prevents water and electrolyte loss from the body—a requirement for life in terrestrial animals like us. Our skin barrier also prevents infectious diseases and allergies by blocking external substances such as pathogens, allergens and chemicals from invading the body. At least that’s how the barrier is supposed to work. But even though many of the microbes that come in contact with or reside on the skin are normally unable to establish an infection, any break in the skin from a cut, scrape, burn or bite can be the entry point of an invading pathogen, such as Ebola virus from the infected blood of a mammalian host or Zika virus from the infected saliva of a mosquito vector. But these aren’t the most frequent ways that our hands participate in the spread of infectious diseases. Rather, our hands are critical in the indirect transmission of pathogens between people via contaminated objects and surfaces, as Mary Mallon did throughout her career. Called fomites, these risky objects are everywhere: phones, faucets, doorknobs, elevator buttons, dishtowels, utensils, food, you name it. We touch these things and the microbes on them literally all the time. Parents won’t be surprised that children can touch objects and surfaces more than 600 times per hour during outdoor play. At the same time, these little explorers might touch their mouths or someone else’s about 20 times an hour. Yet adults do this quite a bit, too. Regardless of age or sex, we might touch our faces up to 800 times a day. Often the touch comes from an automatic and unconscious movement, and so if you think you’re an exception, it could be that you simply don’t remember. For instance, when prompted to recall nonverbal behaviors during interpersonal interactions, the subjects of one study showed the lowest accuracy in estimating how many self-touches they made. Hand contact with the mouth, nose and eyes—sometimes called the facial T-zone by infectious disease researchers—is the riskiest kind of face touching. That’s because the mucous membranes that line these structures can serve as staging grounds for microbial pathogenesis, the process by which microbes cause disease. People have been observed touching their T-zone around eight times an hour in public places, and the number nearly doubles for kids. In medical offices, some health care workers make T-zone touches with the same frequency as people do in public, although clinicians do so slightly less often. But believe it or not, medical students can be even worse. In one study, they were observed touching their face 23 times per hour while listening to a lecture—after completing coursework in infection control and transmission precautions, no less. And almost half of those touches involved contact with a mucous membrane. Hand contacts with fomites and mucous membranes are a potentially dangerous combination. People who are infected with pathogens can expel them from their bodies in saliva, mucus, blood, urine and feces as well as in respiratory secretions in the form of droplets and aerosols. These pathogens can be deposited on or transferred to fomites in a variety of ways, from an explosive sneeze or casual touch. Then the pathogens can survive and remain infectious on fomites for varying lengths of time, from a few hours in some cases to several months in others depending on variables related to the pathogen, the fomite and their environmental conditions. Many people were made aware of these possibilities during the Covid-19 pandemic, when the earliest recommendations from health officials included washing your hands, cleaning surfaces and not touching your face. Some pathogens are more likely than others to spread via fomite and hand-to-hand contact, even if SARS-CoV-2 doesn’t appear to be one of them. This is the case for some gastrointestinal pathogens like Salmonella typhi, norovirus and poliovirus, which usually follow a route of fecal-oral transmission. Others such as Vibrio cholerae (bacteria that cause cholera) and Escherichia coli (bacteria that can cause a variety of infections depending on the strain) are more likely to spread through fecal contamination of food and water. But fomite-mediated transmission is also a concern for some respiratory pathogens like rhinovirus, which is the predominant cause of the common cold. One study found that around 14 percent of the rhinovirus on an individual’s fingers was transferred to another individual via a doorknob or faucet, and half as much via hand-to-hand contact. Furthermore, another study found that after an overnight stay in a hotel, adults with natural rhinovirus colds contaminated about 35 percent of the 150 environmental sites tested, such as pens, light switches, remote controls and telephones. In one-third of the trials, the study’s subjects indirectly transferred the virus to other people’s fingertips up to 18 hours after contaminating these surfaces. If this isn’t an argument for hand hygiene, then I don’t know what is. And this argument long preceded Mallon. In 1847, when Hungarian physician Ignaz Semmelweis devised the interventions that would earn him the title of “the father of hand hygiene,” the discipline of medicine was on the verge of a revolution. Surgeons had just started using general anesthesia when operating on patients, who were able to experience painless operations as never before. Anesthesia was also first used for childbirth in 1845, at a time when maternal death was far too common; in general, for every thousand babies born during the 19th century, as many as ten mothers died. One of the major causes of maternal mortality was childbirth-related septicemia, known as puerperal fever or childbed fever—later found to be caused by Streptococcus pyogenes bacteria. Between 1841 and 1847, puerperal fever was responsible for up to 16 percent of maternal deaths at the hospital in Vienna, where Semmelweis worked. Mothers died far more frequently, however, in one of the hospital’s obstetric wards than in the other one. And Semmelweis seized the opportunity to understand why and how. He examined the mortality statistics at the hospital over decades, finding that the mortality rates of the two wards diverged after 1841. At that time, one of the wards became staffed only with midwives. In the other one, deliveries were performed by medical students and doctors, who also conducted autopsies in a nearby room. After one of the hospital’s pathologists died following a scalpel slip during an autopsy, from which he succumbed to a condition similar to puerperal fever, Semmelweis made the cadaver connection. Concluding that the medical students and obstetricians were causing puerperal fever in their pregnant patients by infecting them with cadaverous particles on their hands, Semmelweis instituted some harsh protocols. Everyone had to scrub their hands with a chlorinated lime solution after leaving the autopsy room and before contact with a patient. Why chlorinated lime? Because Semmelweis didn’t think that soap and water were strong enough to remove the culprits of contagion from post-autopsy hands, and chlorinated lime solution was the strongest product used by the housekeeping staff at the hospital.Excerpted from The Human Disease: How We Create Pandemics, From Our Bodies to Our Beliefs by Sabrina Sholts. Published by The MIT Press. Compilation Copyright Smithsonian Institution © 2024. 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The human hand is an incredible tool—and a deadly threat

Sabrina Sholts

Curator, Anthropology, National Museum of Natural History

“There is no act of life so dangerous to others,” fumed physician Robert Eccles in 1909, “as carelessness concerning the condition of our hands.”

He really meant it. In a seven-page rant titled “Dirty Hands,” published in the Dietetic and Hygienic Gazette of New York City, Eccles blamed filthy fingers for the deadliest crimes of the age. Causing more deaths than “bullets, poisons, railway accidents and earthquakes combined,” the human hand was a weapon of mass destruction that extinguished innocent lives by the hour, according to this Brooklyn-based doctor. And Eccles was fighting back. With ample ammunition from research in bacteriology, a field in its heyday by the close of the 19th century, he had scientific proof that uncleanliness could transform hands into petri dishes of pathogens. “Until the HABIT is established of purifying the hands, both timely and properly, no lessening of this human misery seems possible under existing conditions,” Eccles declared.

The main target of the doctor’s ire was a private cook named Mary Mallon, the notorious “Typhoid Mary” of medical lore, who was serving a sentence of forced isolation on North Brother Island in New York City’s East River. Mallon was arrested as a public health threat in 1907 after being identified as the source of seven household outbreaks of typhoid fever since 1900.

Epidemiological evidence suggested that she infected her clients by preparing their meals with unclean hands—a charge that Mallon rejected. She didn’t deny her poor hand hygiene but also failed to see how she could have infected anyone. Typhoid fever has many symptoms, such as a prolonged high fever, headache and malaise, and Mallon had none of them.

The disease is caused by the bacterium Salmonella typhi, which was well-described and identifiable with diagnostic tests by the 1890s. Untreated typhoid fever can be fatal in up to 30 percent of cases, and before the advent of antibiotics, it caused thousands of deaths in the United States each year. Only humans are infected by and transmit the pathogen, usually through food and water contaminated with Salmonella-filled urine or feces. This is likely how Mallon spread the disease given that laboratory analyses of her feces showed pathogens aplenty, which suggested that none of her trips from the bathroom to the kitchen involved soap.

Typhoid Mary
Vilified as “Typhoid Mary” by the press, Mary Mallon was arrested as a public health threat in 1907. Fotosearch / Stringer via Getty Images

Mallon refused to believe that she was an asymptomatic carrier of typhoid fever, even after her release in 1910. She continued to cook, but she didn’t adopt the hand-washing habit that Eccles preached. Thus he was probably pleased by the further punishment that she faced for her dirty hands when health authorities tracked her down again. After more people had fallen ill and died from her contaminated cuisine, she was arrested and isolated for a second time in 1915, with a sentence that lasted the rest of her life.

The story of Mallon holds many lessons, and the danger of unclean hands is one of them. But still today, disease risks frequently involve pathogens and routes of transmission that we fail to recognize. I recall when virologist Matt Frieman made this point effectively at a workshop in 2017. The scientists in attendance were invited to present and discuss their research with a group of filmmakers, and Matt’s topic was perfect for a Hollywood movie: deadly viruses that have recently emerged in humans. When Matt finished his presentation, one filmmaker asked him how much we needed to worry about these pathogens at present. You could hear the alarm in her voice. And without missing a beat, Matt replied, “Right now, our most immediate threat is a norovirus outbreak from that jar of cookies by the bathrooms.”

He was right. In our meeting venue, arranged by one of the premier scientific organizations in the United States, there was an inviting jar of chocolate chip cookies on a small table … directly on the path to and from the toilets.

Like Salmonella typhi, norovirus is an intestinal pathogen that’s commonly spread through contaminated food, water and surfaces. It’s one of the world’s leading causes of gastroenteritis (also known as stomach flu) and extremely contagious, partly because a small dose can cause infection. Incredibly, a sick person can shed billions of tiny particles of norovirus in their stool and vomit, and it takes as few as 18 of those particles to infect another person. Norovirus is also highly transmissible because it’s picked up and left all over the place by our grabby hands.

For an example, look to the utterly miserable weekend of an Oregon girls soccer team in 2010. While sharing hotel rooms at an out-of-state tournament, several of the team’s members fell ill with acute gastroenteritis. The first girl to become sick—called the index patient—had used a bathroom where a grocery bag of snacks was being stored. She didn’t actually touch the bag or its contents but instead contaminated their surfaces by vomiting, excreting diarrhea and flushing the toilet—all of which can aerosolize noroviruses, thereby making them airborne. The index patient went home the next morning, but cookies, chips and fresh grapes in the grocery bag were passed around at the team’s lunch that afternoon. Within 48 hours, seven other players and chaperones became sick, too.

Sickness is often a helpful signal of infection. It tells the patient, as well as the rest of us, to steer clear. But like Salmonella typhi, norovirus infections can be contagious without any symptoms at all. People can shed the virus in their feces before they start to feel sick or for weeks after they begin to feel better. Hand washing is therefore one of the simplest and most effective ways to prevent transmission. Placing treats far away from the restrooms is another one.

How our hands work

Our hands wouldn’t work so well as disease vectors if we didn’t use them so much. And we wouldn’t use them so much if there weren’t so much that they can do. So before we delve further into a discussion of how humans give a helping hand to pathogens in their transmission, let’s consider what makes our hands so helpful in the first place.

Put one hand flat on a surface, palm down, and you might be able to make out the contours of 14 short bones called phalanges in your thumb and fingers, in addition to five longer ones in your palm called metacarpals that articulate with your wrist. Eight small wrist bones called carpals are mostly hidden from external view. Some of them are surprisingly charismatic in shape, resembling miniature forms of common objects that range from a boot to a boat. But there’s nothing cute about what they do. These 27 bones give each hand its rigid, knuckled structure, while joined and surrounded with muscles, tendons, ligaments, blood vessels and nerves that connect with other elements of the body and carry out directions from the brain. Together they’re critical components of the anatomical architecture that allows your hand to move.

At each of your fingertips there’s an ever-growing, translucent plate of fibrous protein called keratin, otherwise known as a nail. Although they’re nice for decoration, your nails protect and enhance your sensitivity to touch, too. Flip your hand over, and you can better understand how. The nails provide a hard backing for fibrofatty cushions of flesh at each of your fingertips, five fingertip pads in addition to several palm pads on the underside of each hand. Extremely creased and furrowed, these pulpy little pillows of nerve endings have some of the highest concentrations of receptors in all the skin, making them highly sensitive to sensory stimuli. Try them out with a tap or two—but be careful! Fingertip injuries are potentially debilitating and common, particularly in curious young children who use their hands to explore their environment without realizing the physical dangers involved. Even beyond childhood, through touch sensations and tactile perceptions of temperature, texture and vibration transmitted to the brain, fingers are essential to how most people contact and interact with the external world throughout life.

Human hands have some minor distinctions among primates that make a big difference. The human hand can be distinguished from those of other living apes by a high thumb-to-digit ratio, meaning that we have a relatively long thumb when measured against the fingers on the same hand. One major advantage of these hand proportions is that our thumb can be placed squarely in pad-to-pad contact with, or positioned diametrically opposite to, any or all of our fingers. Thumb opposition isn’t unique to humans, and in fact an opposable thumb facilitates the enhanced grasping abilities of many primates. But what sets our thumb apart is its power. Modern humans have a unique combination and greater number of forearm muscles versus other primates, as well as a notable musculature in the thumb. Altogether, these features allow humans to firmly and precisely grip objects for certain types of manipulation that other animals, even our living primate relatives, can’t achieve.

Imagine pinching a piece of paper between your thumb and index finger, for example. We use this type of forceful, pad-to-pad precision gripping without thinking about it, and literally in a snap. Yet it was a breakthrough in human evolution. Other primates exhibit some kinds of precision grips in the handling and use of objects, but not with the kind of efficient opposition that our hand anatomy allows. In a single hand, humans can easily hold and manipulate objects, even small and delicate ones, while adjusting our fingers to their shape and reorienting them with displacements of our fingertip pads. Our relatively long, powerful thumb and other anatomical attributes, including our flat nails (which nearly all primates possess), make this possible. Just picture trying—and failing—to dog-ear a page in a book with pointy, curved claws.

With a unique combination of traits, the human hand shaped history. No question, stone tools couldn’t have become a keystone of human technology and subsistence without hands that could do the job, along with a nervous system that could regulate and coordinate the necessary signals. Even for those who have never attempted to make a spear tip or arrowhead from a rock (which is most of you), it’s obvious that it would require strong grips, constant rotation and repositioning, and forceful, careful strikes with another hard object. And even for those who have done so, it can be a bloody business.

A journey through history and around the globe to examine how and why pandemics are an inescapable threat of our own making.

But our manual dexterity isn’t determined by our hand anatomy alone. Our nervous system, which involves the brain, spinal cord and a complex system of nerves, exerts control over our hand movements. Indeed, neurological factors may partly explain why primate species with similar hands can differ quite a bit in their mechanical abilities. For example, the tufted capuchin and common squirrel monkey both have pseudo-opposable thumbs, but only the capuchin displays relatively independent finger movements and precision gripping in picking up small objects and manipulating tools. Functional differences in their neuroanatomy may be the cause.

Of course, the most common object that people touch nowadays is a screen. And the tap-tap-tap movements of our fingers is a unique human ability, as no other primate can move their fingers as rapidly and independently as we do. Here again, we can thank the extraordinary human brain given that normal finger tapping requires the functional integrity of different parts of our central nervous system. Moreover, repetitive rapid finger tapping is a common test of fine motor control of the upper extremities as well as a standard means of assessing the potential effects of neurodegenerative disease and traumatic brain injury.

Chimp With Newspaper
While a human can turn the page of a book using forceful thumb-finger opposition, other apes can’t form this pad-to-pad “precision grip” due to the relative shortness of the thumb compared to the other fingers, as seen in the left hand of this chimpanzee. Instead, this chimpanzee is gripping the pages of a magazine by holding them between the knuckles of its right hand. Mertie . via Flickr under CC By-SA 2.0 Deed

Our use of information technology, like smartphones and computers, is often described as having the world at our fingertips. But this metaphor makes sense when it comes to microbes, too.

Microbes and our hands

The vast majority of microbes on and in the human body are persistent but harmless colonists. Those on the hand are no exception.

Many of the microbes at our fingertips provide important benefits for human health. For instance, one of the key functions of the skin microbiota, which are mostly bacteria, is acid resistance. By regulating the acidity of the skin, these microbes help to maintain a powerful permeability barrier that prevents water and electrolyte loss from the body—a requirement for life in terrestrial animals like us.

Our skin barrier also prevents infectious diseases and allergies by blocking external substances such as pathogens, allergens and chemicals from invading the body.

At least that’s how the barrier is supposed to work. But even though many of the microbes that come in contact with or reside on the skin are normally unable to establish an infection, any break in the skin from a cut, scrape, burn or bite can be the entry point of an invading pathogen, such as Ebola virus from the infected blood of a mammalian host or Zika virus from the infected saliva of a mosquito vector.

But these aren’t the most frequent ways that our hands participate in the spread of infectious diseases. Rather, our hands are critical in the indirect transmission of pathogens between people via contaminated objects and surfaces, as Mary Mallon did throughout her career. Called fomites, these risky objects are everywhere: phones, faucets, doorknobs, elevator buttons, dishtowels, utensils, food, you name it. We touch these things and the microbes on them literally all the time.

Parents won’t be surprised that children can touch objects and surfaces more than 600 times per hour during outdoor play. At the same time, these little explorers might touch their mouths or someone else’s about 20 times an hour. Yet adults do this quite a bit, too. Regardless of age or sex, we might touch our faces up to 800 times a day. Often the touch comes from an automatic and unconscious movement, and so if you think you’re an exception, it could be that you simply don’t remember. For instance, when prompted to recall nonverbal behaviors during interpersonal interactions, the subjects of one study showed the lowest accuracy in estimating how many self-touches they made.

Hand contact with the mouth, nose and eyes—sometimes called the facial T-zone by infectious disease researchers—is the riskiest kind of face touching. That’s because the mucous membranes that line these structures can serve as staging grounds for microbial pathogenesis, the process by which microbes cause disease. People have been observed touching their T-zone around eight times an hour in public places, and the number nearly doubles for kids. In medical offices, some health care workers make T-zone touches with the same frequency as people do in public, although clinicians do so slightly less often. But believe it or not, medical students can be even worse. In one study, they were observed touching their face 23 times per hour while listening to a lecture—after completing coursework in infection control and transmission precautions, no less. And almost half of those touches involved contact with a mucous membrane.

Hand contacts with fomites and mucous membranes are a potentially dangerous combination. People who are infected with pathogens can expel them from their bodies in saliva, mucus, blood, urine and feces as well as in respiratory secretions in the form of droplets and aerosols. These pathogens can be deposited on or transferred to fomites in a variety of ways, from an explosive sneeze or casual touch. Then the pathogens can survive and remain infectious on fomites for varying lengths of time, from a few hours in some cases to several months in others depending on variables related to the pathogen, the fomite and their environmental conditions. Many people were made aware of these possibilities during the Covid-19 pandemic, when the earliest recommendations from health officials included washing your hands, cleaning surfaces and not touching your face.

Some pathogens are more likely than others to spread via fomite and hand-to-hand contact, even if SARS-CoV-2 doesn’t appear to be one of them.

This is the case for some gastrointestinal pathogens like Salmonella typhi, norovirus and poliovirus, which usually follow a route of fecal-oral transmission. Others such as Vibrio cholerae (bacteria that cause cholera) and Escherichia coli (bacteria that can cause a variety of infections depending on the strain) are more likely to spread through fecal contamination of food and water.

But fomite-mediated transmission is also a concern for some respiratory pathogens like rhinovirus, which is the predominant cause of the common cold. One study found that around 14 percent of the rhinovirus on an individual’s fingers was transferred to another individual via a doorknob or faucet, and half as much via hand-to-hand contact. Furthermore, another study found that after an overnight stay in a hotel, adults with natural rhinovirus colds contaminated about 35 percent of the 150 environmental sites tested, such as pens, light switches, remote controls and telephones.

In one-third of the trials, the study’s subjects indirectly transferred the virus to other people’s fingertips up to 18 hours after contaminating these surfaces. If this isn’t an argument for hand hygiene, then I don’t know what is.

And this argument long preceded Mallon.

In 1847, when Hungarian physician Ignaz Semmelweis devised the interventions that would earn him the title of “the father of hand hygiene,” the discipline of medicine was on the verge of a revolution. Surgeons had just started using general anesthesia when operating on patients, who were able to experience painless operations as never before. Anesthesia was also first used for childbirth in 1845, at a time when maternal death was far too common; in general, for every thousand babies born during the 19th century, as many as ten mothers died. One of the major causes of maternal mortality was childbirth-related septicemia, known as puerperal fever or childbed fever—later found to be caused by Streptococcus pyogenes bacteria. Between 1841 and 1847, puerperal fever was responsible for up to 16 percent of maternal deaths at the hospital in Vienna, where Semmelweis worked. Mothers died far more frequently, however, in one of the hospital’s obstetric wards than in the other one. And Semmelweis seized the opportunity to understand why and how.

He examined the mortality statistics at the hospital over decades, finding that the mortality rates of the two wards diverged after 1841. At that time, one of the wards became staffed only with midwives. In the other one, deliveries were performed by medical students and doctors, who also conducted autopsies in a nearby room. After one of the hospital’s pathologists died following a scalpel slip during an autopsy, from which he succumbed to a condition similar to puerperal fever, Semmelweis made the cadaver connection.

Concluding that the medical students and obstetricians were causing puerperal fever in their pregnant patients by infecting them with cadaverous particles on their hands, Semmelweis instituted some harsh protocols. Everyone had to scrub their hands with a chlorinated lime solution after leaving the autopsy room and before contact with a patient. Why chlorinated lime? Because Semmelweis didn’t think that soap and water were strong enough to remove the culprits of contagion from post-autopsy hands, and chlorinated lime solution was the strongest product used by the housekeeping staff at the hospital.

Excerpted from The Human Disease: How We Create Pandemics, From Our Bodies to Our Beliefs

by Sabrina Sholts. Published by The MIT Press. Compilation Copyright Smithsonian Institution © 2024. All rights reserved.

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Giant Sloths and Many Other Massive Creatures Were Once Common on Our Planet. With Environmental Changes, Such Giants Could Thrive Again

If large creatures like elephants, giraffes and bison are allowed to thrive, they could alter habitats that allow for the rise of other giants

Giant Sloths and Many Other Massive Creatures Were Once Common on Our Planet. With Environmental Changes, Such Giants Could Thrive Again If large creatures like elephants, giraffes and bison are allowed to thrive, they could alter habitats that allow for the rise of other giants Riley Black - Science Correspondent July 11, 2025 8:00 a.m. Ancient sloths lived in trees, on mountains, in deserts, in boreal forests and on open savannas. Some grew as large as elephants. Illustration by Diego Barletta The largest sloth of all time was the size of an elephant. Known to paleontologists as Eremotherium, the shaggy giant shuffled across the woodlands of the ancient Americas between 60,000 and five million years ago. Paleontologists have spent decades hotly debating why such magnificent beasts went extinct, the emerging picture involving a one-two punch of increasing human influence on the landscape and a warmer interglacial climate that began to change the world’s ecosystems. But even less understood is how our planet came to host entire communities of such immense animals during the Pleistocene. Now, a new study on the success of the sloths helps to reveal how the world of Ice Age giants came to be, and hints that an Earth brimming with enormous animals could come again. Florida Museum of Natural History paleontologist Rachel Narducci and colleagues tracked how sloths came to be such widespread and essential parts of the Pleistocene Americas and published their findings in Science this May. The researchers found that climate shifts that underwrote the spread of grasslands allowed big sloths to arise, the shaggy mammals then altering those habitats to maintain open spaces best suited to big bodies capable of moving long distances. The interactions between the animals and environment show how giants attained their massive size, and how strange it is that now our planet has fewer big animals than would otherwise be here. Earth still boasts some impressively big species. In fact, the largest animal of all time is alive right now and only evolved relatively recently. The earliest blue whale fossils date to about 1.5 million years ago, and, at 98 feet long and more than 200 tons, the whale is larger than any mammoth or dinosaur. Our planet has always boasted a greater array of small species than large ones, even during prehistoric ages thought of as synonymous with megafauna. Nevertheless, Earth’s ecosystems are still in a megafaunal lull that began at the close of the Ice Age. “I often say we are living on a downsized planet Earth,” says University of Maine paleoecologist Jacquelyn Gill.Consider what North America was like during the Pleistocene, between 11,000 years and two million ago. The landmass used to host multiple forms of mammoths, mastodons, giant ground sloths, enormous armadillos, multiple species of sabercat, huge bison, dire wolves and many more large creatures that formed ancient ecosystems unlike anything on our planet today. In addition, many familiar species such as jaguars, black bears, coyotes, white-tailed deer and golden eagles also thrived. Elsewhere in the world lived terror birds taller than an adult human, wombats the size of cars, woolly rhinos, a variety of elephants with unusual tusks and other creatures. Ecosystems capable of supporting such giants have been the norm rather than the exception for tens of millions of years. Giant sloths were among the greatest success stories among the giant-size menagerie. The herbivores evolved on South America when it was still an island continent, only moving into Central and North America as prehistoric Panama connected the landmasses about 2.7 million years ago. Some were small, like living two- and three-toed sloths, while others embodied a range of sizes all the way up to elephant-sized giants like Eremotherium and the “giant beast” Megatherium. An Eremotherium skeleton at the Houston Museum of Natural Science demonstrates just how large the creature grew. James Nielsen / Houston Chronicle via Getty Images The earliest sloths originated on South America about 35 million years ago. They were already big. Narducci and colleagues estimate that the common ancestor of all sloths was between about 150 and 770 pounds—or similar to the range of sizes seen among black bears today—and they walked on the ground. “I was surprised and thrilled” to find that sloths started off large, Narducci says, as ancestral forms of major mammal groups are often small, nocturnal creatures. The earliest sloths were already in a good position to shift with Earth’s climate and ecological changes. The uplift of the Andes Mountains in South America led to changes on the continent as more open, drier grasslands spread where there had previously been wetter woodlands and forests. While some sloths became smaller as they spent more time around and within trees, the grasslands would host the broadest diversity of sloth species. The grasslands sloths were the ones that ballooned to exceptional sizes. Earth has been shifting between warmer and wetter times, like now, and cooler and drier climates over millions of years. The chillier and more arid times are what gave sloths their size boost. During these colder spans, bigger sloths were better able to hold on to their body heat, but they also didn’t need as much water, and they were capable of traveling long distances more efficiently thanks to their size. “The cooler and drier the climate, especially after 11.6 million years ago, led to expansive grasslands, which tends to favor the evolution of increasing body mass,” Narducci says. The combination of climate shifts, mountain uplift and vegetation changes created environments where sloths could evolve into a variety of forms—including multiple times when sloths became giants again. Gill says that large body size was a “winning strategy” for herbivores. “At a certain point, megaherbivores get so large that most predators can’t touch them; they’re able to access nutrition in foods that other animals can’t really even digest thanks to gut microbes that help them digest cellulose, and being large means you’re also mobile,” Gill adds, underscoring advantages that have repeatedly pushed animals to get big time and again. The same advantages underwrote the rise of the biggest dinosaurs as well as more recent giants like the sloths and mastodons. As large sloths could travel further, suitable grassland habitats stretched from Central America to prehistoric Florida. “This is what also allowed for their passage into North America,” Narducci says. Sloths were able to follow their favored habitats between continents. If the world were to shift back toward cooler and drier conditions that assisted the spread of the grasslands that gave sloths their size boost, perhaps similar giants could evolve. The sticking point is what humans are doing to Earth’s climate, ecosystems and existing species. The diversity and number of large species alive today is vastly, and often negatively, affected by humans. A 2019 study of human influences on 362 megafauna species, on land and in the water, found that 70 percent are diminishing in number, and 59 percent are getting dangerously close to extinction. But if that relationship were to change, either through our actions or intentions, studies like the new paper on giant sloths hint that ecosystems brimming with a wealth of megafaunal species could evolve again. Big animals change the habitats where they live, which in turn tends to support more large species adapted to those environments. The giant sloths that evolved among ancient grasslands helped to keep those spaces open in tandem with other big herbivores, such as mastodons, as well as the large carnivores that preyed upon them. Paleontologists and ecologists know this from studies of how large animals such as giraffes and rhinos affect vegetation around them. Big herbivores, in particular, tend to keep habitats relatively open. Elephants and other big beasts push over trees, trample vegetation underfoot, eat vast amounts of greenery and transport seeds in their dung, disassembling vegetation while unintentionally planting the beginnings of new habitats. Such broad, open spaces were essential to the origins of the giant sloths, and so creating wide-open spaces helps spur the evolution of giants to roam such environments. For now, we are left with the fossil record of giant animals that were here so recently that some of their bones aren’t even petrified, skin and fur still clinging to some skeletons. “The grasslands they left behind are just not the same, in ways we’re really only starting to understand and appreciate,” Gill says. A 2019 study on prehistoric herbivores in Africa, for example, found that the large plant-eaters altered the water cycling, incidence of fire and vegetation of their environment in a way that has no modern equivalent and can’t just be assumed to be an ancient version of today’s savannas. The few megaherbivores still with us alter the plant life, water flow, seed dispersal and other aspects of modern environments in their own unique ways, she notes, which should be a warning to us to protect them—and the ways in which they affect our planet. If humans wish to see the origin of new magnificent giants like the ones we visit museums to see, we must change our relationship to the Earth first. Get the latest Science stories in your inbox.

How changes in California culture have influenced the evolution of wild animals in Los Angeles

A new study argues that religion, politics and war affect how animals and plants in cities evolve, and the confluence of these forces seem to be actively affecting urban wildlife in L.A.

For decades, biologists have studied how cities affect wildlife by altering food supplies, fragmenting habitats and polluting the environment. But a new global study argues that these physical factors are only part of the story. Societal factors, the researchers claim, especially those tied to religion, politics and war, also leave lasting marks on the evolutionary paths of the animals and plants that share our cities.Published in Nature Cities, the comprehensive review synthesizes evidence from cities worldwide, revealing how human conflict and cultural practices affect wildlife genetics, behavior and survival in urban environments.The paper challenges the tendency to treat the social world as separate from ecological processes. Instead, the study argues, we should consider the ways the aftershocks of religious traditions, political systems and armed conflicts can influence the genetic structure of urban wildlife populations. (Gabriella Angotti-Jones / Los Angeles Times) “Social sciences have been very far removed from life sciences for a very long time, and they haven’t been integrated,” said Elizabeth Carlen, a biologist at Washington University in St. Louis and co-lead author of the study. “We started just kind of playing around with what social and cultural processes haven’t been talked about,” eventually focusing on religion, politics and war because of their persistent yet underexamined impacts on evolutionary biology, particularly in cities, where cultural values and built environments are densely concentrated.Carlen’s own work in St. Louis examines how racial segregation and urban design, often influenced by policing strategies, affect ecological conditions and wild animals’ access to green spaces.“Crime prevention through environmental design,” she said, is one example of how these factors influence urban wildlife. “Law enforcement can request that there not be bushes … or short trees, because then they don’t have a sight line across the park.” Although that design choice may serve surveillance goals, it also limits the ability of small animals to navigate those spaces.These patterns, she emphasized, aren’t unique to St. Louis. “I’m positive that it’s happening in Los Angeles. Parks in Beverly Hills are going to look very different than parks in Compton. And part of that is based on what policing looks like in those different places.” This may very well be the case, as there is a significantly lower level of urban tree species richness in areas like Compton than in areas like Beverly Hills, according to UCLA’s Biodiversity Atlas. A coyote wanders onto the fairway, with the sprinklers turned on, as a golfer makes his way back to his cart after hitting a shot on the 16th hole of the Harding golf course at Griffith Park. (Mel Melcon / Los Angeles Times) The study also examines war and its disruptions, which can have unpredictable effects on animal populations. Human evacuation from war zones can open urban habitats to wildlife, while the destruction of green spaces or contamination of soil and water can fragment ecosystems and reduce genetic diversity.In Kharkiv, Ukraine, for example, human displacement during the Russian invasion led to the return of wild boars and deer to urban parks, according to the study. In contrast, sparrows, which depend on human food waste, nearly vanished from high-rise areas.All of this, the researchers argue, underscores the need to rethink how cities are designed and managed by recognizing how religion, politics and war shape not just human communities but also the evolutionary trajectories of urban wildlife. By integrating ecological and social considerations into urban development, planners and scientists can help create cities that are more livable for people while also supporting the long-term genetic diversity and adaptability of the other species that inhabit them.This intersection of culture and biology may be playing out in cities across the globe, including Los Angeles.A study released earlier this year tracking coyotes across L.A. County found that the animals were more likely to avoid wealthier neighborhoods, not because of a lack of access or food scarcity, but possibly due to more aggressive human behavior toward them and higher rates of “removal” — including trapping and releasing elsewhere, and in some rare cases, killing them. In lower-income areas, where trapping is less common, coyotes tended to roam more freely, even though these neighborhoods often had more pollution and fewer resources that would typically support wild canines. Researchers say these patterns reflect how broader urban inequities are written directly into the movements of and risks faced by wildlife in the city.Black bears, parrots and even peacocks tell a similar story in Los Angeles. Wilson Sherman, a PhD student at UCLA who is studying human-black bear interactions, highlights how local politics and fragmented municipal governance shape not only how animals are managed but also where they appear. (Carolyn Cole / Los Angeles Times) “Sierra Madre has an ordinance requiring everyone to have bear-resistant trash cans,” Sherman noted. “Neighboring Arcadia doesn’t.” This kind of patchwork governance, Sherman said, can influence where wild animals ultimately spend their time, creating a mosaic of risk and opportunity for species whose ranges extend across multiple jurisdictions.Cultural values also play a role. Thriving populations of non-native birds, such as Amazon parrots and peacocks, illustrate how aesthetic preferences and everyday choices can significantly influence the city’s ecological makeup in lasting ways.Sherman also pointed to subtler, often overlooked influences, such as policing and surveillance infrastructure. Ideally, the California Department of Fish and Wildlife would be the first agency to respond in a “wildlife situation,” as Sherman put it. But, he said, what often ends up happening is that people default to calling the police, especially when the circumstances involve animals that some urban-dwelling humans may find threatening, like bears.Police departments typically do not possess the same expertise and ability as CDFW to manage and then relocate bears. If a bear poses a threat to human life, police policy is to kill the bear. However, protocols for responding to wildlife conflicts that are not life-threatening can vary from one community to another. And how police use non-lethal methods of deterrence — such as rubber bullets and loud noises — can shape bear behavior.Meanwhile, the growing prevalence of security cameras and motion-triggered alerts has provided residents with new forms of visibility into urban biodiversity. “That might mean that people are suddenly aware that a coyote is using their yard,” Sherman said. In turn, that could trigger a homeowner to purposefully rework the landscape of their property so as to discourage coyotes from using it. Surveillance systems, he said, are quietly reshaping both public perception and policy around who belongs in the city, and who doesn’t. A mountain lion sits in a tree after being tranquilized along San Vicente Boulevard in Brentwood on Oct. 27, 2022. (Wally Skalij / Los Angeles Times) Korinna Domingo, founder and director of the Cougar Conservancy, emphasized how cougar behavior in Los Angeles is similarly shaped by decades of urban development, fragmented landscapes and the social and political choices that structure them. “Policies like freeway construction, zoning and even how communities have been historically policed or funded can affect where and how cougars move throughout L.A.,” she said. For example, these forces have prompted cougars to adapt by becoming more nocturnal, using culverts or taking riskier crossings across fragmented landscapes.Urban planning and evolutionary consequences are deeply intertwined, Domingo says. For example, mountain lion populations in the Santa Monica and Santa Ana mountains have shown signs of reduced genetic diversity due to inbreeding, an issue created not by natural processes, but by political and planning decisions — such as freeway construction and zoning decisions— that restricted their movement decades ago.Today, the Wallis Annenberg Wildlife Crossing, is an attempt to rectify that. The massive infrastructure project is happening only, Domingo said, “because of community, scientific and political will all being aligned.”However, infrastructure alone isn’t enough. “You can have habitat connectivity all you want,” she said, but you also have to think about social tolerance. Urban planning that allows for animal movement also increases the likelihood of contact with people, pets and livestock — which means humans need to learn how to interact with wild animals in a healthier way.In L.A., coexistence strategies can look very different depending on the resources, ordinances and attitudes of each community. Although wealthier residents may have the means to build predator-proof enclosures, others lack the financial or institutional support to do the same. And some with the means simply choose not to, instead demanding lethal removal., “Wildlife management is not just about biology,” Domingo said. “It’s about values, power, and really, who’s at the table.”Wildlife management in the United States has long been informed by dominant cultural and religious worldviews, particularly those grounded in notions of human exceptionalism and control over nature. Carlen, Sherman and Domingo all brought up how these values shaped early policies that framed predators as threats to be removed rather than species to be understood or respected. In California, this worldview contributed not only to the widespread killing of wolves, bears and cougars but also to the displacement of American Indian communities whose land-based practices and beliefs conflicted with these approaches. A male peacock makes its way past Ian Choi, 21 months old, standing in front of his home on Altura Road in Arcadia. (Mel Melcon / Los Angeles Times) Wildlife management in California, specifically, has long been shaped by these same forces of violence, originating in bounty campaigns not just against predators like cougars and wolves but also against American Indian peoples. These intertwined legacies of removal, extermination and land seizure continue to influence how certain animals and communities are perceived and treated today.For Alan Salazar, a tribal elder with the Fernandeño Tataviam Band of Mission Indians, those legacies run deep. “What happened to native peoples happened to our large predators in California,” he said. “Happened to our plant relatives.” Reflecting on the genocide of Indigenous Californians and the coordinated extermination of grizzly bears, wolves and mountain lions, Salazar sees a clear parallel.“There were three parts to our world — the humans, the animals and the plants,” he explained. “We were all connected. We respected all of them.” Salazar explains that his people’s relationship with the land, animals and plants is itself a form of religion, one grounded in ceremony, reciprocity and deep respect. Salazar said his ancestors lived in harmony with mountain lions for over 10,000 years, not by eliminating them but by learning from them. Other predators — cougars, bears, coyotes and wolves — were also considered teachers, honored through ceremony and studied for their power and intelligence. “Maybe we had a better plan on how to live with mountain lions, wolves and bears,” he said. “Maybe you should look at tribal knowledge.”He views the Wallis Annenberg Wildlife Crossing — for which he is a Native American consultant — as a cultural opportunity. “It’s not just for mountain lions,” he said. “It’s for all animals. And that’s why I wanted to be involved.” He believes the project has already helped raise awareness and shift perceptions about coexistence and planning, and hopes that it will help native plants, animals and peoples.As L.A. continues to grapple with the future of wildlife in its neighborhoods, canyons and corridors, Salazar and others argue that it is an opportunity to rethink the cultural frameworks, governance systems and historical injustices that have long shaped human-animal relations in the city. Whether through policy reform, neighborhood education or sacred ceremony, residents need reminders that evolutionary futures are being shaped not only in forests and preserves but right here, across freeways, backyards and local council meetings. The Wallis Annenberg Wildlife Crossing under construction over the 101 Freeway near Liberty Canyon Road in Agoura Hills on July 12, 2024. (Myung J. Chun / Los Angeles Times) The research makes clear that wildlife is not simply adapting to urban environments in isolation; it is adapting to a range of factors, including policing, architecture and neighborhood design. Carlen believes this opens a crucial frontier for interdisciplinary research, especially in cities like Los Angeles, where uneven geographies, biodiversity and political decisions intersect daily. “I think there’s a lot of injustice in cities that are happening to both humans and wildlife,” she said. “And I think the potential is out there for justice to be brought to both of those things.”

Something Strange Is Happening to Tomatoes Growing on the Galápagos Islands

Scientists say wild tomato plants on the archipelago's western islands are experiencing "reverse evolution" and reverting back to ancestral traits

Something Strange Is Happening to Tomatoes Growing on the Galápagos Islands Scientists say wild tomato plants on the archipelago’s western islands are experiencing “reverse evolution” and reverting back to ancestral traits Sarah Kuta - Daily Correspondent July 9, 2025 4:29 p.m. Scientists are investigating the production of ancestral alkaloids by tomatoes in the Galápagos Islands. Adam Jozwiak / University of California, Riverside Some tomatoes growing on the Galápagos Islands appear to be going back in time by producing the same toxins their ancestors did millions of years ago. Scientists describe this development—a controversial process known as “reverse evolution”—in a June 18 paper published in the journal Nature Communications. Tomatoes are nightshades, a group of plants that also includes eggplants, potatoes and peppers. Nightshades, also known as Solanaceae, produce bitter compounds called alkaloids, which help fend off hungry bugs, animals and fungi. When plants produce alkaloids in high concentrations, they can sicken the humans who eat them. To better understand alkaloid synthesis, researchers traveled to the Galápagos Islands, the volcanic chain roughly 600 miles off the coast of mainland Ecuador made famous by British naturalist Charles Darwin. They gathered and studied more than 30 wild tomato plants growing in different places on various islands. The Galápagos tomatoes are the descendents of plants from South America that were probably carried to the archipelago by birds. The team’s analyses revealed that the tomatoes growing on the eastern islands were behaving as expected, by producing alkaloids that are similar to those found in modern, cultivated varieties. But those growing on the western islands, they found, were creating alkaloids that were more closely related to those produced by eggplants millions of years ago. Tomatoes growing on the western islands (shown here) are producing ancestral alkaloids.  Adam Jozwiak / University of California, Riverside Researchers suspect the environment may be responsible for the plants’ unexpected return to ancestral alkaloids. The western islands are much younger than the eastern islands, so the soil is less developed and the landscape is more barren. To survive in these harsh conditions, perhaps it was advantageous for the tomato plants to revert back to older alkaloids, the researchers posit. “The plants may be responding to an environment that more closely resembles what their ancestors faced,” says lead author Adam Jozwiak, a biochemist at the University of California, Riverside, to BBC Wildlife’s Beki Hooper. However, for now, this is just a theory. Scientists say they need to conduct more research to understand why tomato plants on the western islands have adapted this way. Scientists were able to uncover the underlying molecular mechanisms at play: Four amino acids in a single enzyme appear to be responsible for the reversion back to the ancestral alkaloids, they found. They also used evolutionary modeling to confirm the direction of the adaptation—that is, that the tomatoes on the western islands had indeed returned to an earlier, ancestral state. Among evolutionary biologists, “reverse evolution” is somewhat contentious. The commonly held belief is that evolution marches forward, not backward. It’s also difficult to prove an organism has reverted back to an older trait through the same genetic pathways. But, with the new study, researchers say they’ve done exactly that. “Some people don’t believe in this,” says Jozwiak in a statement. “But the genetic and chemical evidence points to a return to an ancestral state. The mechanism is there. It happened.” So, if “reverse evolution” happened in wild tomatoes, could something similar happen in humans? In theory, yes, but it would take a long time, Jozwiak says. “If environmental conditions shifted dramatically over long timescales, it’s possible that traits from our distant past could re-emerge, but whether that ever happens is highly uncertain,” Jozwiak tells Newsweek’s Daniella Gray. “It’s speculative and would take millions of years, if at all.” Get the latest stories in your inbox every weekday.

Lifesize herd of puppet animals begins climate action journey from Africa to Arctic Circle

The Herds project from the team behind Little Amal will travel 20,000km taking its message on environmental crisis across the worldHundreds of life-size animal puppets have begun a 20,000km (12,400 mile) journey from central Africa to the Arctic Circle as part of an ambitious project created by the team behind Little Amal, the giant puppet of a Syrian girl that travelled across the world.The public art initiative called The Herds, which has already visited Kinshasa and Lagos, will travel to 20 cities over four months to raise awareness of the climate crisis. Continue reading...

Hundreds of life-size animal puppets have begun a 20,000km (12,400 mile) journey from central Africa to the Arctic Circle as part of an ambitious project created by the team behind Little Amal, the giant puppet of a Syrian girl that travelled across the world.The public art initiative called The Herds, which has already visited Kinshasa and Lagos, will travel to 20 cities over four months to raise awareness of the climate crisis.It is the second major project from The Walk Productions, which introduced Little Amal, a 12-foot puppet, to the world in Gaziantep, near the Turkey-Syria border, in 2021. The award-winning project, co-founded by the Palestinian playwright and director Amir Nizar Zuabi, reached 2 million people in 17 countries as she travelled from Turkey to the UK.The Herds’ journey began in Kinshasa’s Botanical Gardens on 10 April, kicking off four days of events. It moved on to Lagos, Nigeria, the following week, where up to 5,000 people attended events performed by more than 60 puppeteers.On Friday the streets of Dakar in Senegal will be filled with more than 40 puppet zebras, wildebeest, monkeys, giraffes and baboons as they run through Médina, one of the busiest neighbourhoods, where they will encounter a creation by Fabrice Monteiro, a Belgium-born artist who lives in Senegal, and is known for his large-scale sculptures. On Saturday the puppets will be part of an event in the fishing village of Ngor.The Herds’ 20,000km journey began in Kinshasa, the Democratic Republic of the Congo. Photograph: Berclaire/walk productionsThe first set of animal puppets was created by Ukwanda Puppetry and Designs Art Collective in Cape Town using recycled materials, but in each location local volunteers are taught how to make their own animals using prototypes provided by Ukwanda. The project has already attracted huge interest from people keen to get involved. In Dakar more than 300 artists applied for 80 roles as artists and puppet guides. About 2,000 people will be trained to make the puppets over the duration of the project.“The idea is that we’re migrating with an ever-evolving, growing group of animals,” Zuabi told the Guardian last year.Zuabi has spoken of The Herds as a continuation of Little Amal’s journey, which was inspired by refugees, who often cite climate disaster as a trigger for forced migration. The Herds will put the environmental emergency centre stage, and will encourage communities to launch their own events to discuss the significance of the project and get involved in climate activism.The puppets are created with recycled materials and local volunteers are taught how to make them in each location. Photograph: Ant Strack“The idea is to put in front of people that there is an emergency – not with scientific facts, but with emotions,” said The Herds’ Senegal producer, Sarah Desbois.She expects thousands of people to view the four events being staged over the weekend. “We don’t have a tradition of puppetry in Senegal. As soon as the project started, when people were shown pictures of the puppets, they were going crazy.”Little Amal, the puppet of a Syrian girl that has become a symbol of human rights, in Santiago, Chile on 3 January. Photograph: Anadolu/Getty ImagesGrowing as it moves, The Herds will make its way from Dakar to Morocco, then into Europe, including London and Paris, arriving in the Arctic Circle in early August.

Dead, sick pelicans turning up along Oregon coast

So far, no signs of bird flu but wildlife officials continue to test the birds.

Sick and dead pelicans are turning up on Oregon’s coast and state wildlife officials say they don’t yet know why. The Oregon Department of Fish and Wildlife says it has collected several dead brown pelican carcasses for testing. Lab results from two pelicans found in Newport have come back negative for highly pathogenic avian influenza, also known as bird flu, the agency said. Avian influenza was detected in Oregon last fall and earlier this year in both domestic animals and wildlife – but not brown pelicans. Additional test results are pending to determine if another disease or domoic acid toxicity caused by harmful algal blooms may be involved, officials said. In recent months, domoic acid toxicity has sickened or killed dozens of brown pelicans and numerous other wildlife in California. The sport harvest for razor clams is currently closed in Oregon – from Cascade Head to the California border – due to high levels of domoic acid detected last fall.Brown pelicans – easily recognized by their large size, massive bill and brownish plumage – breed in Southern California and migrate north along the Oregon coast in spring. Younger birds sometimes rest on the journey and may just be tired, not sick, officials said. If you find a sick, resting or dead pelican, leave it alone and keep dogs leashed and away from wildlife. State wildlife biologists along the coast are aware of the situation and the public doesn’t need to report sick, resting or dead pelicans. — Gosia Wozniacka covers environmental justice, climate change, the clean energy transition and other environmental issues. Reach her at gwozniacka@oregonian.com or 971-421-3154.Our journalism needs your support. Subscribe today to OregonLive.com.

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