Conspicuous consumption may drive fertility down

"As competition becomes more focused on social climbing, as opposed to just putting food on the table, people invest more in material goods and achieving social status, and that affects how many children they have," says anthropologist Paul Hooper.

By Carol Clark

Competition for social status may be an important driver of lower fertility in the modern world, suggests a new study published in Philosophical Transactions of the Royal Society B.

“The areas were we see the greatest declines in fertility are areas with modern labor markets that have intense competition for jobs and an overwhelming diversity of consumer goods available to signal well-being and social status,” says senior author Paul Hooper, an anthropologist at Emory University. “The fact that many countries today have so much social inequality – which makes status competition more intense – may be an important part of the explanation.”

The study authors developed a mathematical model showing that their argument is plausible from a biological point of view.

Across the globe, from the United States to the United Kingdom to India, fertility has gone down as inequality and the cost of achieving social status has gone up. “Our model shows that as competition becomes more focused on social climbing, as opposed to just putting food on the table, people invest more in material goods and achieving social status, and that affects how many children they have,” Hooper says.

Factors such as lower child mortality rates, more access to birth control and the choice to delay childbirth to get a higher education are also associated with declining fertility. “While these factors are very important they are insufficient to explain the drops in family sizes that we are seeing,” Hooper says.

In addition to Hooper, the study authors include anthropologists Mary Shenk, from the University of Missouri, and Hillard Kaplan, from the University of New Mexico. They are pioneers in an emerging field of “computational anthropology,” which blends methods from biology, economics, computer science and physics to answer fundamental questions about human behavior.

The study is featured in a special issue of the Philosophical Transactions of the Royal Society B, devoted to how evolutionary approaches can help solve the puzzle of why human fertility varies substantially.

Hooper first became intrigued by variability in human fertility while researching the Tsimane indigenous people of Bolivian Amazonia. The Tsimane (pronounced chee-mahn-AY in Spanish) are foragers and horticulturalists who live in small, isolated communities along the Maniqui River in the Amazonian rainforest.

“In a hunter-gatherer society, parents have a limited number of things available to invest in: Food, clothing and shelter,” Hooper says. “The average Tsimane family has nine children and they can provide these basic needs for all of them.”

Hooper noticed a pattern, however, when Tsimane families leave the rainforest and move closer to Spanish-speaking towns where they come into contact with market economies and industrialized goods. “When they start getting earnings for the first time, they spend money on things you wouldn’t really expect, like an expensive wristwatch or a nylon backpack for a child attending school, instead of sending them with a traditional woven bag,” Hooper says. “I got the impression that these things were largely symbolic of their social status and competence.”

The Tsimane family size also tends to drop when they move closer to town, he adds: From eight or nine children in remote villages, to five or six in villages near town, to three to four in the town itself. 

Hooper hypothesizes that a similar pattern plays out as societies develop from mainly agrarian to more urban and affluent. “In my grandparents day, it took a lot less investment to be respectable,” he says. “It was important to have a set of good clothes for church on Sunday but you could let the kids run around barefoot for the rest of the week.”

Today, however, keeping up with the Jones has become much more complicated – and expensive. 

“The human species is highly social and, as a result, we appear to have an ingrained desire for social standing,” Hooper says. “The problem is that our brains evolved in a radically different environment from that of the modern world. Evolution didn’t necessarily train us very well for the almost infinite size of our communities, the anonymity of many of our interactions and the vast numbers of goods that we can use to signal our status. Our evolved psychology may be misfiring and causing us to over invest in social standing.”

Related:
Amazonian study quantifies key role of grandparents in family nutrition

Image: Thinkstockphoto.com

Mixed-strain malaria infections influence drug resistance

A boy awaits treatment at a malaria clinic in Myanmar. Resistance to the one remaining drug for the most lethal species of malaria parasite, Plasmodium falciparum, has emerged in Southeast Asia.

By Carol Clark

Scientists have documented for the first time how competition among different malaria parasite strains in human hosts could influence the spread of drug resistance.

“We found that when hosts are co-infected with drug-resistant and drug-sensitive strains, both strains are competitively suppressed,” says Mary Bushman, lead author of the study and a PhD candidate in Emory University’s Population Biology, Ecology and Evolution Graduate Program. “Anti-malarial therapy, by clearing drug-sensitive parasites from mixed infections, may result in competitive release of resistant strains.”

Proceedings of the Royal Society B published the research, led by the labs of Jaap de Roode, an evolutionary biologist at Emory, and Venkatachalam Udhayakumar, a malaria expert from the Centers of Disease Control and Prevention’s Division of Parasitic Diseases and Malaria.

Almost half of the world’s population is at risk for malaria, a complex disease caused by five species of Plasmodium parasites that are transmitted to humans by 30 to 40 different species of mosquitoes that all behave differently. The current study focused on Plasmodium falciparum, the most common malaria parasite on the continent of Africa and the one responsible for the most malaria-related deaths globally.

P. falciparum has developed resistance to former first-line therapies chloroquine and sulfadoxine-pyrimethamine. “We’re now down to our last treatment, artemisinin combination therapy, or ACT, and resistance to that recently emerged in Southeast Asia,” Bushman says. “If ACT resistance continues to follow the same pattern, the world may soon be without reliable antimalarial drugs.”

People infected with P. falciparum often have multiple strains of the parasite – especially in high-transmission areas such as sub-Saharan Africa where infectious mosquito bites occur frequently. Many people have developed partial immunity, making asymptomatic infections common and further complicating control efforts.

The researchers knew from previous work, by de Roode and others, that competition between mixed strains of malaria parasites in laboratory mice are a crucial determinant to the spread of resistance. “In the mouse studies we found that drug-sensitive parasites suppress resistant parasites,” de Roode says. “We also found that by clearing these sensitive parasites with drugs, the resistant parasites had a big advantage, growing up to high numbers and transmitting to mosquitoes at high rates. Ever since doing that work, I have wanted to see if the same could apply to humans.”

The researchers drew from 1,300 blood samples of untreated children with malaria from Angola, Ghana and Tanzania. They extracted DNA of malaria parasites from the blood samples and used polymerase chain reaction (PCR) technology to determine the densities of drug-resistant strains and drug-sensitive ones. About 15 percent of the blood samples had mixtures of both types.

The results showed that in mixed-strain infections, densities of chloroquine-sensitive and chloroquine-resistant strains were reduced in the presence of competitors. They also showed that, in the absence of chloroquine, the resistant strains had lower densities compared with sensitive strains.

“The results were really clear cut, which rarely happens in human studies,” Bushman says. “We found almost complete consistency between the three data sets.”

Currently, Bushman says, the tendency is to use “one-size-fits-all” strategies for controlling malaria but more tailored approaches are needed.

A strategy of mass drug administration might be effective, for example, in a place with a low prevalence of malaria and less likelihood of mixed-strain infections. That same strategy, however, might actually boost drug resistance without reducing the burden of disease in areas where most of the population is infected with multiple strains of malaria parasites.

“The epidemiology of malaria infection is different for different places and different conditions,” Bushman says. “We hope that our work will spur development of new strategies to minimize resistance while maximizing the benefits of control measures.”

More questions must be answered to guide the development of these new strategies. “As a first step,” de Roode says, “we need to determine if the observed suppression of resistance in humans also results in reduced transmission to mosquitoes.”

Another limitation of the current study was that it was focused entirely on blood samples from children that had not been treated with drugs. “We need to find out if drug treatment of people infected with malaria removes competition and gives resistance a boost, as we have found in mice before,” de Roode says.

The study was funded by the Burroughs Wellcome Fund Institutional Program Unifying Population and Laboratory-based Science, Emory University, the Association of Public Health Laboratories, the CDC and the National Institutes of Health.

Image: iStockphoto.com

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Atlanta Science Festival fosters 'small steps, big ideas'

Emory faculty and students are set to dazzle children with science demonstrations at "Physics Live!" The event will take place on Friday, March 25 from 3:30 to 7 pm in Emory's Math and Science Building. 

By Carol Clark

"Small steps, big ideas," is the theme of the third annual Atlanta Science Festival, which encourages all ages to step into a world of wonder and exploration through more than 100 events and hands-on activities in metro-Atlanta from March 19 to March 26. In fact, the party has already started via ongoing online activities, such as a chance to vote for Atlanta's favorite scientist and compose original "sci-ku" — or science-themed haiku.

About 50,000 people are expected to turn out during the eight-day festival for talks, lab tours, film screenings, participatory activities and science demonstrations. The events are set at more than 80 different venues, including the Emory campus.

"We've got a lot of fun and irreverent events, like 'The Science of Circus," and others that are more on the serious side, like a discussion on climate change," says Jordan Rose, who is executive co-director of the festival along with Meisa Salaita. "There is something for everyone, from little kids to teens, college students and adults."

A new event this year, "Sci-Cycle: A Competitive Scavenger Hunt on Two Wheels," will start things rolling on the opening day of the festival, Saturday, March 19. The Emory Spokes Council and the Emory Graduate Sustainability Group are organizing the bike adventure, to take place on the Atlanta Beltline. Participants will learn about materials science, urban foraging and sustainable practices through pedaling to various locations and performing tasks such as using a bicycle-powered blender to make a smoothie.

Also new this year is a "Science Parade," set for the final day of the festival, on Saturday, March 26, starting at the Centennial Academy in downtown Atlanta. "Everyone is welcome to join the parade," Rose says. "We're encouraging people to come dressed as their favorite scientist, or element or other science-themed character."

The half-mile parade, led by the Seed and Feed Marching Abominable band, will end at Centennial Olympic Park for the launch of the Exploration Expo, the culminating event of the Atlanta Science Festival. The free Expo includes stage performances and hands-on science activities at 100-plus exhibitor booths, including more than a dozen run by Emory faculty and students.

Highlights of this year's Expo will include a giant LEGO build of the city of Atlanta, which will be 40-feet wide upon completion. "Everyone can help assemble a bit of it throughout the Expo," Rose says.

A range of Atlanta Science Festival events will take place on the Emory and Oxford campuses, as well as the Carter Center.

"The Atlanta Science Festival is a great way to feature some of the research and discoveries that are coming out of Emory for the local community," Rose says. "It's also a great platform for Emory students and faculty to practice their communication skills for a general audience, and to engage the public in their science."

Click here for a full listing of Emory events, and details about how to join them.

Dopamine key to vocal learning, songbird study finds

"Bengalese finches are songbirds that have extremely precise singing behavior and can also refine their songs in response to auditory feedback," says Emory biologist Samuel Sober. "This provides a way for us to understand similar patterns of learning in humans." (Emory Photo/Video)

By Carol Clark

The neurotransmitter dopamine is essential to correcting vocal mistakes, suggests a study on Bengalese finches. The Journal of Neuroscience published the research, led by Emory biologist Samuel Sober, who uses Bengalese finches as a model to understand how the brain learns.

“Our experiments are the first to isolate the role of dopamine in sensory-motor learning, as distinct from the other functions that dopamine performs in the brain,” Sober says. “Bengalese finches are songbirds that have extremely precise singing behavior and can also refine their songs in response to auditory feedback. This provides a way for us to understand similar patterns of learning in humans. The ability to use auditory feedback to fix errors in behavior underlies everything from learning to speak, to sing and to play an instrument.”

The research found that a reduction in dopamine levels in a small region of the basal ganglia in the finches’ brains caused a reduction in their ability to correct vocal errors, while having no detectable effect on their ability to sing. The basal ganglia is situated at the base of the forebrain and is associated with a variety of functions, including voluntary motor movements and procedural learning.

“Some neurons send messages to the basal ganglia using dopamine,” Sober explains. “These dopamine-containing cells are some of the same neurons that slowly die off over years in patients with Parkinson’s Disease, and problems with vocal control are often observed in Parkinson’s patients. We hope that our research may help with the understanding of the role of dopamine in vocal behavior and the development of potential therapies for learning deficits.”

A great deal of scientific literature already exists on the role of dopamine in learning to associate a stimulus with a reward or a punishment. What’s much less understood is how dopamine may play a role in learning to perform a skilled behavior, such as speaking.

To conduct the experiments on the Bengalese finches, the researchers first recorded each bird singing while an occasional blast of white noise was emitted from a speaker near the cage when the bird sang within a particular range of pitches. “The finch interprets this blast of noise as an error,” Sober explains. “We measured how fast each bird changed its pitch to avoid that noise.”

A drug was then administered to the birds to lower the dopamine levels in their basal ganglia by about half and their singing was once again recorded. “We found that their ability to correct their singing in response to the white noise also went down by about half,” Sober says. “They were still able to learn from the white noise ‘mistake,’ but they were significantly worse at it.”

While the experiment demonstrates that dopamine is necessary for processing vocal errors, many questions remain. “We don’t know if reducing the level of dopamine changes the birds’ ability to detect a vocal mistake, or whether it just affects their ability to fix mistakes once they detect them, or perhaps both,” Sober says. “Our next step is to better understand, at the cellular and molecular level, how changes in dopamine affect activity in the basal ganglia.”

The research was funded by the Morris K. Udall Center of Excellence for Parkinson’s Disease Research at Emory, part of a network of centers managed by the National Institutes of Health to foster research into the causes and possible treatments for Parkinson’s Disease, and by the National Institute for Neurological Disorders and Stroke. Co-authors of the study include Emory post-doctoral fellow Li He and graduate students Lukas Hoffmann, Varun Saravanan and Alynda Wood.

Related:
Birdsong study pecks theory that music is uniquely human
Singing in the brain: Songbirds sing like humans
How songbirds learn to sing 

A scientist's view from Earth's highest mountains

"As difficult and dangerous as mountain climbing can be, it's also an absolutely wonderful experience. You have to live it to understand it," says Stefan Lutz, chair of chemistry at Emory, shown during a Denali expedition.

By Carol Clark

In December of 2012, Stefan Lutz summited the 22,841-foot peak of Aconcagua, the highest mountain in the Western hemisphere, located in western Argentina. “The view from the top was amazing. When you look to the horizon and see the curvature of the Earth, you realize that you’re in a pretty special place,” says Lutz, professor and chair of chemistry at Emory. He is also a dedicated mountaineer who will attempt to climb Mount Everest this spring.

After a few minutes spent admiring the view from atop Aconcagua, it was time to descend. Lutz and a guide maneuvered down a particularly steep section and sat down to wait for the rest of their group.

“It was a beautiful day. I remember drinking and eating a bit of food, just trying to re-energize myself,” Lutz says. “Then I noticed a man, a climber I didn’t know, standing alone, maybe 20 feet away. He just kept standing, still as a statue. It’s exhausting at that altitude and I wondered, ‘Why doesn’t he sit down?’”

Lutz mentioned it to the guide who then approached the man. “As soon as the guide put his hand on the guy’s shoulder, he collapsed,” Lutz recalls.

They gave him some water and asked, “Do you know where you are?”

“Yes,” the man replied, “I’m on Mount Fuji.”

It was clear that the confused mountaineer, a Japanese man climbing solo, was suffering acute mountain sickness. “He was in serious trouble,” Lutz says. “Luckily, some Argentine park rangers came along. They gave him bottled oxygen which helped him recover enough that he could be helped back down the mountain.”

Without the assistance of the rangers, the climber’s condition might have progressed to high altitude cerebral edema – a severe and, if untreated, fatal form of altitude sickness when capillary fluid leaks into the blood-brain barrier due to the effects of inadequate oxygen.

“That’s the highest I’ve climbed – 22,841 feet,” Lutz says. “It’s very humbling. Even a fit person moves like a turtle at that altitude.”

Bright sunshine at 3 a.m. during a Denali expedition in Alaska.

The experience was another stark reminder to Lutz, who is 46, that his passion for climbing comes with great risks along with the rewards. “It’s not about being a thrill seeker,” Lutz says, trying to explain why he climbs. “As difficult and dangerous as mountain climbing can be, it's also an absolutely wonderful experience. You have to live it to understand it. You get a high from it that stays with you.”

A native of Switzerland, Lutz grew up hiking and being in the mountains. Five years ago, he became more serious about his hobby and started a quest to climb the Seven Summits – the highest peak on each of the continents. He leaves March 26 for Nepal and a two-month expedition to climb Mount Everest. If his Everest bid is successful, it will mark the sixth of the Seven Summits for Lutz. You can follow his team’s progress on the web site of the expedition leader, International Mountain Guides.

As part of his physical conditioning, Lutz never takes the elevator as he roams around the Emory Chemistry Center. Instead, he climbs the stairs with his large, red, expedition backpack – loaded with 60 pounds of sand – strapped to his six-foot-four frame.

Lutz is a biomolecular chemist who uses protein engineering to develop catalysts for therapeutic and industrial applications. He also enjoys teaching, and takes examples from his climbing experiences into the classroom to convey some of the complex concepts in biochemistry. “Using my mountaineering experiences brings these concepts to life and gets students more engaged,” Lutz says. “Most of them have experienced at least a hint of what I talk about, like the feeling you get at higher altitudes when hiking or skiing, so they relate to it.”

Lutz’ scientific training deepens his understanding of extreme landscapes and the physical and mental processes a climber may experience. Following is a bit of Lutz’ perspective on mountaineering, in his words and photos.

Landing in Antarctica for an expedition up Mount Vinson, the most remote, and the least climbed, of the Seven Summits.

The environment of the southern polar region 

At 16,050 feet, Mount Vinson is the highest peak in Antarctica. To get there, you start with a five-hour flight on a jet plane from Punta Arenas on the southern tip of South America to an icy airfield in the center of Antarctica. Next, you get in a DC3 fitted with skis for a 45-minute flight that sets you down nearer Mount Vinson. From there, you take an even smaller propeller plan to reach the base camp.

Antarctica stores about 65 percent of all the fresh water in the world in the form of ice. You fly over an area of incredible beauty and realize that it looks the same as it did tens of thousands of years ago. No human being has touched it and many places have had no precipitation for more than 100,000 years – just snow drifts. Antarctica is the driest continent and is actually one of the marvelous, great deserts of Earth. Humidity is in the single digits and it feels like you are in an evaporator, turning into dried fruit. The temperature routinely drops to minus 40 degrees Fahrenheit. You look to the horizon and all you see is snow, and more snow, and a few rocks. It’s beautiful in its simplicity.

We were there in December, which is mid-summer in the southern hemisphere. Since we were only about 700 miles from the South Pole, bright sunshine streamed into our tents even at 2 a.m. The snow is like a mirror. You have to wear glacier sunglasses all the time or you can go snow blind within 15 minutes. Every speck of exposed skin has to be covered with a thick layer of sunblock to avoid massive sunburn. We had one team member who forgot to put sunblock on the bottom of his nose and ended up with a really painful burn of his nostrils.

Above the clouds: Lutz makes his way up the West Buttress Ridge of Denali, with Mount Foraker in the background.

The physiology of extreme cold 

Denali in Alaska is North America’s highest peak at 20,310 feet. It’s at about 63 degrees northern latitude. To reach base camp, you fly in a single-prop plane between snow-covered peaks and land on a glacier. The plane takes off and you and your teammates are now about 70 miles away from any human habitation and, basically, living in a freezer for three weeks. The average temperature is around 0 degrees Fahrenheit. Everything that you need to climb and to survive for the next 20 days is loaded into a 60-pound pack that you carry on your back and on a sled that you pull behind you, which holds another 50 pounds.

As you work your way up the mountain, your metabolism goes into overdrive to provide sufficient muscle energy and maintain body heat in the cold. That turns climbing into an all-you-can-eat contest. I switched from my normal 2000-calorie-per-day diet to about 12,000 calories per day. And I still lost 12 pounds during my three weeks climbing the mountain! Believe it or not, it’s not easy consuming this amount of calories. At higher elevations, your appetite diminishes. Food that tastes delicious at sea level suddenly becomes unappealing as your taste perception changes. Experience has taught me to leave behind my beloved salami when climbing and instead stuff my pockets with Snickers bars and chocolate-covered raisins. I ate about 25 pounds of candy during the Denali trip. 

Burning calories to generate energy and heat is an oxidation process, and the higher you go, the less oxygen in the atmosphere. To manage the extreme altitude of Mount Everest, which is 29,035 feet, most climbers use supplemental oxygen to stay warm. You can wear lots of insulating gear but if you are not getting enough oxygen to burn fuel, you still start shivering. And if shivering is not enough to warm you up, you can develop hypothermia. At the same time, you are at risk for frostbite – the result of your body saying, “I can live without my fingers and toes, arms and legs.” It pulls your blood into your core to make sure your critical organs have sufficient blood supply. That process can happen faster at higher altitude.

Roped together on Denali. "You form a unique bond with the people that you climb with, the people on the same rope as you," Lutz says.

The biochemistry of altitude sickness

The summit of Denali has 50 percent less oxygen than at sea level. Atop Everest that percentage drops to 30 percent. Even without exercising these low oxygen levels can make you feel like you’re suffocating. You start to breathe faster to take in more oxygen but with each breath, you also exhale carbon dioxide.

Carbon dioxide is part of a buffer system in the bloodstream that prevents the pH level in cells to fluctuate. All the proteins in our cells rely on steady acidity. But if you pump out too much carbon dioxide from your body, the buffer system goes haywire and you can develop a condition called alkalosis.

Respiratory alkalosis, which is a result of blood pH rising beyond the normal range, starts off as a mild headache but can quickly progress to severe head pain and nausea. Worst of all, it has little to do with fitness. I’ve seen very strong athletes crumple up with these symptoms. If untreated, you start vomiting violently, leading to more dehydration. The condition can progress to where cellular fluid starts leading from your brain, known as cerebral edema, or your lungs, known as pulmonary edema. 

Medication such as Diamox can help the body more quickly adjust to higher altitude but the best approach is to slowly and gradually hike to higher elevations. That gives your body time to acclimatize to the thin air. It’s the reason that climbers spend nearly two months at the Everest base camp before attempting to reach the summit.

Navigating ice crevices of Denali. "Fear can become your ally by keeping you focused and alert," Lutz says.

The psychology of endurance and fear 

Mountaineering is an endurance sport but only part of that is physical endurance. A majority of it comes from your head. It can take sheer willpower to keep you going when you are cold and exhausted. Your mind has to convince your body to take the next step, hour after hour, as you work your way towards a summit. On the flip side, you can have a sunny day, blue sky and no wind and know that you are going to make it. Psychologically, it’s a breakthrough moment: A feeling that no money can buy.

The summit, however, is only the halfway point. A majority of mountaineering accidents happen during the descent. People are euphoric, but also exhausted physically and mentally. You can never let down your inner guard because you’re operating in an environment with little room for error. All it takes is one misstep.

Fear can become your ally by keeping you focused and alert. I remember traversing a narrow section on Denali called the Windy Corner. To one side of you is a rock wall. On the other side are ice crevices big enough to swallow a school bus. Rocks the size of fists fall from that rock wall and you have to dodge them almost like you are in a computer game. If a rock hits your lower body it can shatter a bone. If one hits you on the head, it can kill you. Getting through there only took a few minutes but it’s an experience that I won’t forget.

Fear can also give you strength. While climbing in the Denali range, we were roped together in groups of four as a safety precaution due to all of the crevices. One moment we were moving through a snowy glacier landscape. The next moment, one of our team members in the group just ahead of mine simply disappeared. There was no sound, just the sight of the rope running. His body had broken through a bridge of thin snow and was plummeting into a dark abyss in the ice. The team members he was roped to immediately dropped to the ground and anchored their axes into the ice to stop the fall. They then used the rope and their gear to quickly build a pulley system and extract our comrade from the crevice. After about 20 minutes of hard work by the team he was back on the glacier surface, shaken but unhurt. You would think they would be too fatigued from climbing to respond so quickly and energetically, but in a situation like that your heart rate spikes and your adrenaline level goes through the roof.

Lutz, in yellow parka, enjoys a brief celebration with teammates after they reached the summit of Denali. "These are the kinds of friendships that last forever," he says.

The sociology of bonding during intense experiences 

You forge a unique bond with the people that you climb with, the people on the same rope as you. You’re putting your lives in one another’s hands.

On Aconcagua, two of my teammates and I were crammed into our small tent one night when a ferocious blizzard hit, with winds up to 80 miles-per-hour. Nobody wants to be out in that kind of weather. Yet, every hour or so, one of us had to crawl out and dig out the tent so we would not get buried in snow. We took turns shoveling. Meanwhile, the two inside the tent made sure they had a hot drink ready when the other one finished a round.

Pulling together as a team to overcome tremendous challenges, in spite of everyone being mentally and physically exhausted, builds deep camaraderie. These are the kinds of friendships that last forever.

Related:
How a hike in the woods led to a math 'Aha!'
The math of rock climbing
Proving math is good for endurance sports

All photos by Stefan Lutz or courtesy of Stefan Lutz.