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Jun. 29th, 2013 09:35 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
conulyMountain Populations Offer Clues to Human Evolution
http://nyti.ms/17ukLKh
May 30, 2013
Mountain Populations Offer Clues to Human Evolution
By CARL ZIMMER
In the hearts of evolutionary biologists, mountains occupy a special place. It’s not just their physical majesty: mountains also have an unmatched power to drive human evolution. Starting tens of thousands of years ago, people moved to high altitudes, and there they experienced natural selection that has reworked their biology.
“This is the most extreme example in humans that you can find,” said Rasmus Nielsen, an evolutionary biologist at the University of California at Berkeley.
Humans have adapted to mountainous environments just as Charles Darwin predicted. To discover how this occurred, scientists are now examining the DNA of people who scaled mountains in different parts of the world.
“There’s this beautiful experiment in natural selection going on,” says Anna Di Rienzo, a professor of human genetics at the University of Chicago. “You can really ask questions central to evolutionary biology.”
When people from low elevations climb to higher ones, they start struggling for oxygen. At 12,000 feet, each breath delivers only 60 percent of the oxygen that the same breath would at sea level. Even a slow walk can be exhausting, because the body can get so little fuel.
In the face of this stress, people respond in several ways. They produce more hemoglobin, the molecule that ferries oxygen from the lungs. Their resting heart rate increases, as does their breath rate. These adjustments help raise the amount of oxygen in the blood, but it never regains its former level.
Extra hemoglobin is not a good long-term solution to life at high altitudes, because it can lead to blood clots. Women moving from low altitudes to high ones also have more trouble delivering oxygen to their babies during pregnancy. Studies have shown that the rate of low-birth-weight babies is twice as high at 6,000 feet as it is at sea level.
Life in the mountains is easier for people whose ancestors have lived there for millenniums. They don’t suffer from altitude sickness. Women from high-altitude populations give birth to normal-size babies.
Scientists visiting some of those populations have discovered a number of biological adaptations in the inhabitants’ bodies. In Tibet, for example, people have broader arteries and capillaries. In the Andes, they can dissolve more oxygen into their blood.
Evolutionary biologists reasoned that natural selection produced these adaptations as each population settled at a high elevation. People with mutations that let them withstand low oxygen levels would be more likely to survive and have healthy children. Several teams of scientists have traveled to the mountains to gather DNA samples from people and search for traces of that evolution.
In 2010, Dr. Nielsen and his colleagues found variants of certain genes that were much more common in Tibetans than in the Han, the major ethnic group in China, who have lived for thousands of years at lower altitudes. By a wide margin, the winner was a gene called EPAS1. People with different variants turned out to have different levels of hemoglobin, suggesting that the gene was important to adapting to life at high altitudes.
Recently, Dr. Nielsen and another group of colleagues published a study on people who live in the highlands of Ethiopia. They found no evidence that EPAS1 had evolved there as it did in Tibet. Instead, a different gene, BHLHE41, appeared to have experienced natural selection.
Two other teams of scientists have recently searched for high-altitude genes in Ethiopians, and neither put BHLHE41 on their list. It’s possible that Dr. Nielsen’s method is more sensitive than the others, but that remains to be proved. “It’s going to take a while to sort through the discrepancies in Ethiopia,” said Dr. Di Rienzo, a co-author of one of the other studies.
It will be intriguing to see that unfold. BHLHE41 and EPAS1 turn out to have something in common: they work together in a network of genes that lets us cope with low oxygen levels. Even at sea level, low oxygen can threaten our bodies from time to time. Exercise can strip it from our muscles, while inflammation can eliminate it from wounds. The oxygen-sensing pathway triggers defenses to protect our bodies from damage.
Dr. Nielsen’s study suggests that evolution has stumbled across a way to retool this pathway to help people live at high altitudes. But it turns out there’s more than one way to retool a pathway. Though evolution has some creative freedom, it seems to stick to a few themes.
With Treetop Trail, Philadelphia Zoo Opens Grounds to Prowlers
http://nyti.ms/1997nZA
It comes with pictures:
http://nyti.ms/14hn7qm
PHILADELPHIA — Near the entrance to the Philadelphia Zoo, a new, long tubular cage hangs about 20 feet above the ground, twisting through trees and around buildings as it leads into the zoo’s densely packed campus.
If they are lucky, visitors will see monkeys or lemurs that have decided to leave their regular quarters to explore other areas using the stainless-steel mesh structure.
The installation is part of the zoo’s expanding trail system, designed to provide more variety and stimulation for the animals and bring them closer to visitors. It is the start of a multiyear plan that will extend throughout the zoo’s 42 acres, allowing a variety of species, even bears and lions, to wander from place to place (though at different times) and rotating them through habitats.
While other zoos, like Denver’s and the National Zoo in Washington, have adopted trail systems in limited areas, the Philadelphia Zoo is the world’s first with a plan to rotate animals throughout its grounds.
On a recent day, a red-capped mangabey, a primate native to West Africa, sat in the 700-foot-long Treetop Trail, the first phase of the project, attracting the attention of schoolchildren pouring into the zoo.
Farther along the trail, which rises as high as 37 feet, a group of white-faced saki monkeys ventured out from the primate house, where a notice explained their absence.
“If you don’t see me here, please look outside on the Treetop Trail,” it said.
The trails are the latest development in a movement by zoos worldwide to improve animal welfare and to simulate the wild more closely, said Paul Boyle, senior vice president for conservation and education at the Association of Zoos and Aquariums.
At zoos that allow animals to move outside their traditional enclosures, there are signs that the animals breed more frequently and are less likely to indicate boredom, Dr. Boyle said. For visitors, particularly children, enhanced animal mobility increases understanding about how the creatures live and may build support for conservation of endangered species, he said.
“It’s a win for animals, a win for people and a win for the zoo,” Dr. Boyle said.
As a rare snow leopard slunk across a bridge connecting two parts of the Philadelphia Zoo trail, visitors waiting below grew excited.
“I have a problem with animals being caged,” said Robin DeLisser, 36, from Delray Beach, Fla., who was visiting with her children, Dillan, 11, and Kaelyn, 10. “This gives them more mobility.”
Starting next spring, the big cats will be able to roam outside their quarters on a new trail that will also be open, at different times, to great apes like orangutans.
The final stage of the project, which officials hope will be complete by 2017, will create a trail for other large ground-dwelling animals including zebras, hippos and the zoo’s solitary white rhino.
The last trail might also allow the zoo to reintroduce elephants after shipping out the last of its much-loved pachyderms in 2009 because of concern that the zoo would never have the space or financial resources to ensure their welfare, said Andrew Baker, the zoo’s chief operating officer.
For now, the zoo is raising funds for construction of the second phase, which is expected to cost $5.5 million. The first phase, which included a 1,035-foot extension of Treetop Trail, cost $5.8 million.
By allowing them to get closer to the animals, the Philadelphia Zoo hopes to encourage its 1.2 million annual visitors, particularly children, to understand and act on the conservation that is an increasingly important part of its mission.
Outside KidZooU, a children’s section that opened in mid-April, youngsters are encouraged to “act like an animal” by climbing rope netting shaped like the extension of the trail system next to it, where monkeys and lemurs are allowed to wander.
The young visitors are then invited inside the children’s zoo, where hands-on exhibits make a clear link between the survival of familiar animals and everyday choices that children can make.
As a model of a worried-looking polar bear leans through a living-room window against a background of melting icebergs, children can use a computer terminal to win points for energy-conservation measures like turning off lights to slow the climate change that is threatening the bear’s survival.
By loading cereal boxes onto a conveyor for recycling, children are told, they can reduce the energy consumption that is contributing to global warming and threatening the habitat of the much-loved budgerigar, or budgie. A small flock lives next to the recycling exhibit.
Like the trail system, the children’s zoo aims to foster a conservation ethic among the younger generation, Dr. Baker said. “We are creating a high degree of receptivity to the conservation message that we have to share,” he said.
http://nyti.ms/17ukLKh
May 30, 2013
Mountain Populations Offer Clues to Human Evolution
By CARL ZIMMER
In the hearts of evolutionary biologists, mountains occupy a special place. It’s not just their physical majesty: mountains also have an unmatched power to drive human evolution. Starting tens of thousands of years ago, people moved to high altitudes, and there they experienced natural selection that has reworked their biology.
“This is the most extreme example in humans that you can find,” said Rasmus Nielsen, an evolutionary biologist at the University of California at Berkeley.
Humans have adapted to mountainous environments just as Charles Darwin predicted. To discover how this occurred, scientists are now examining the DNA of people who scaled mountains in different parts of the world.
“There’s this beautiful experiment in natural selection going on,” says Anna Di Rienzo, a professor of human genetics at the University of Chicago. “You can really ask questions central to evolutionary biology.”
When people from low elevations climb to higher ones, they start struggling for oxygen. At 12,000 feet, each breath delivers only 60 percent of the oxygen that the same breath would at sea level. Even a slow walk can be exhausting, because the body can get so little fuel.
In the face of this stress, people respond in several ways. They produce more hemoglobin, the molecule that ferries oxygen from the lungs. Their resting heart rate increases, as does their breath rate. These adjustments help raise the amount of oxygen in the blood, but it never regains its former level.
Extra hemoglobin is not a good long-term solution to life at high altitudes, because it can lead to blood clots. Women moving from low altitudes to high ones also have more trouble delivering oxygen to their babies during pregnancy. Studies have shown that the rate of low-birth-weight babies is twice as high at 6,000 feet as it is at sea level.
Life in the mountains is easier for people whose ancestors have lived there for millenniums. They don’t suffer from altitude sickness. Women from high-altitude populations give birth to normal-size babies.
Scientists visiting some of those populations have discovered a number of biological adaptations in the inhabitants’ bodies. In Tibet, for example, people have broader arteries and capillaries. In the Andes, they can dissolve more oxygen into their blood.
Evolutionary biologists reasoned that natural selection produced these adaptations as each population settled at a high elevation. People with mutations that let them withstand low oxygen levels would be more likely to survive and have healthy children. Several teams of scientists have traveled to the mountains to gather DNA samples from people and search for traces of that evolution.
In 2010, Dr. Nielsen and his colleagues found variants of certain genes that were much more common in Tibetans than in the Han, the major ethnic group in China, who have lived for thousands of years at lower altitudes. By a wide margin, the winner was a gene called EPAS1. People with different variants turned out to have different levels of hemoglobin, suggesting that the gene was important to adapting to life at high altitudes.
Recently, Dr. Nielsen and another group of colleagues published a study on people who live in the highlands of Ethiopia. They found no evidence that EPAS1 had evolved there as it did in Tibet. Instead, a different gene, BHLHE41, appeared to have experienced natural selection.
Two other teams of scientists have recently searched for high-altitude genes in Ethiopians, and neither put BHLHE41 on their list. It’s possible that Dr. Nielsen’s method is more sensitive than the others, but that remains to be proved. “It’s going to take a while to sort through the discrepancies in Ethiopia,” said Dr. Di Rienzo, a co-author of one of the other studies.
It will be intriguing to see that unfold. BHLHE41 and EPAS1 turn out to have something in common: they work together in a network of genes that lets us cope with low oxygen levels. Even at sea level, low oxygen can threaten our bodies from time to time. Exercise can strip it from our muscles, while inflammation can eliminate it from wounds. The oxygen-sensing pathway triggers defenses to protect our bodies from damage.
Dr. Nielsen’s study suggests that evolution has stumbled across a way to retool this pathway to help people live at high altitudes. But it turns out there’s more than one way to retool a pathway. Though evolution has some creative freedom, it seems to stick to a few themes.
With Treetop Trail, Philadelphia Zoo Opens Grounds to Prowlers
http://nyti.ms/1997nZA
It comes with pictures:
http://nyti.ms/14hn7qm
PHILADELPHIA — Near the entrance to the Philadelphia Zoo, a new, long tubular cage hangs about 20 feet above the ground, twisting through trees and around buildings as it leads into the zoo’s densely packed campus.
If they are lucky, visitors will see monkeys or lemurs that have decided to leave their regular quarters to explore other areas using the stainless-steel mesh structure.
The installation is part of the zoo’s expanding trail system, designed to provide more variety and stimulation for the animals and bring them closer to visitors. It is the start of a multiyear plan that will extend throughout the zoo’s 42 acres, allowing a variety of species, even bears and lions, to wander from place to place (though at different times) and rotating them through habitats.
While other zoos, like Denver’s and the National Zoo in Washington, have adopted trail systems in limited areas, the Philadelphia Zoo is the world’s first with a plan to rotate animals throughout its grounds.
On a recent day, a red-capped mangabey, a primate native to West Africa, sat in the 700-foot-long Treetop Trail, the first phase of the project, attracting the attention of schoolchildren pouring into the zoo.
Farther along the trail, which rises as high as 37 feet, a group of white-faced saki monkeys ventured out from the primate house, where a notice explained their absence.
“If you don’t see me here, please look outside on the Treetop Trail,” it said.
The trails are the latest development in a movement by zoos worldwide to improve animal welfare and to simulate the wild more closely, said Paul Boyle, senior vice president for conservation and education at the Association of Zoos and Aquariums.
At zoos that allow animals to move outside their traditional enclosures, there are signs that the animals breed more frequently and are less likely to indicate boredom, Dr. Boyle said. For visitors, particularly children, enhanced animal mobility increases understanding about how the creatures live and may build support for conservation of endangered species, he said.
“It’s a win for animals, a win for people and a win for the zoo,” Dr. Boyle said.
As a rare snow leopard slunk across a bridge connecting two parts of the Philadelphia Zoo trail, visitors waiting below grew excited.
“I have a problem with animals being caged,” said Robin DeLisser, 36, from Delray Beach, Fla., who was visiting with her children, Dillan, 11, and Kaelyn, 10. “This gives them more mobility.”
Starting next spring, the big cats will be able to roam outside their quarters on a new trail that will also be open, at different times, to great apes like orangutans.
The final stage of the project, which officials hope will be complete by 2017, will create a trail for other large ground-dwelling animals including zebras, hippos and the zoo’s solitary white rhino.
The last trail might also allow the zoo to reintroduce elephants after shipping out the last of its much-loved pachyderms in 2009 because of concern that the zoo would never have the space or financial resources to ensure their welfare, said Andrew Baker, the zoo’s chief operating officer.
For now, the zoo is raising funds for construction of the second phase, which is expected to cost $5.5 million. The first phase, which included a 1,035-foot extension of Treetop Trail, cost $5.8 million.
By allowing them to get closer to the animals, the Philadelphia Zoo hopes to encourage its 1.2 million annual visitors, particularly children, to understand and act on the conservation that is an increasingly important part of its mission.
Outside KidZooU, a children’s section that opened in mid-April, youngsters are encouraged to “act like an animal” by climbing rope netting shaped like the extension of the trail system next to it, where monkeys and lemurs are allowed to wander.
The young visitors are then invited inside the children’s zoo, where hands-on exhibits make a clear link between the survival of familiar animals and everyday choices that children can make.
As a model of a worried-looking polar bear leans through a living-room window against a background of melting icebergs, children can use a computer terminal to win points for energy-conservation measures like turning off lights to slow the climate change that is threatening the bear’s survival.
By loading cereal boxes onto a conveyor for recycling, children are told, they can reduce the energy consumption that is contributing to global warming and threatening the habitat of the much-loved budgerigar, or budgie. A small flock lives next to the recycling exhibit.
Like the trail system, the children’s zoo aims to foster a conservation ethic among the younger generation, Dr. Baker said. “We are creating a high degree of receptivity to the conservation message that we have to share,” he said.
