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【计时一】
Even Low-Level Radioactivity Is Damaging, Scientists Conclude
ScienceDaily (Nov. 13, 2012) — Even the very lowest levels of radiation are harmful to life, scientists have concluded in the Cambridge Philosophical Society's journal Biological Reviews. Reporting the results of a wide-ranging analysis of 46 peer-reviewed studies published over the past 40 years, researchers from the University of South Carolina and the University of Paris-Sud found that variation in low-level, natural background radiation was found to have small, but highly statistically significant, negative effects on DNA as well as several measures of health. [attachimg=425,282]109822[/attachimg]
The review is a meta-analysis of studies of locations around the globe that have very high natural background radiation as a result of the minerals in the ground there, including Ramsar, Iran, Mombasa, Kenya, Lodeve, France, and Yangjiang, China. These, and a few other geographic locations with natural background radiation that greatly exceeds normal amounts, have long drawn scientists intent on understanding the effects of radiation on life. Individual studies by themselves, however, have often only shown small effects on small populations from which conclusive statistical conclusions were difficult to draw. "When you're looking at such small effect sizes, the size of the population you need to study is huge," said co-author Timothy Mousseau, a biologist in the College of Arts and Sciences at the University of South Carolina. "ooling across multiple studies, in multiple areas, and in a rigorous statistical manner provides a tool to really get at these questions about low-level radiation." Mousseau and co-author Anders Møller of the University of Paris-Sud combed the scientific literature, examining more than 5,000 papers involving natural background radiation that were narrowed to 46 for quantitative comparison. The selected studies all examined both a control group and a more highly irradiated population and quantified the size of the radiation levels for each. Each paper also reported test statistics that allowed direct comparison between the studies. The organisms studied included plants and animals, but had a large preponderance of human subjects. Each study examined one or more possible effects of radiation, such as DNA damage measured in the lab, prevalence of a disease such as Down's Syndrome, or the sex ratio produced in offspring. For each effect, a statistical algorithm was used to generate a single value, the effect size, which could be compared across all the studies. 【385】
【计时二】
The scientists reported significant negative effects in a range of categories, including immunology, physiology, mutation and disease occurrence. The frequency of negative effects was beyond that of random chance. "There's been a sentiment in the community that because we don't see obvious effects in some of these places, or that what we see tends to be small and localized, that maybe there aren't any negative effects from low levels of radiation," said Mousseau. "But when you do the meta-analysis, you do see significant negative effects." "It also provides evidence that there is no threshold below which there are no effects of radiation," he added. "A theory that has been batted around a lot over the last couple of decades is the idea that is there a threshold of exposure below which there are no negative consequences. These data provide fairly strong evidence that there is no threshold -- radiation effects are measurable as far down as you can go, given the statistical power you have at hand." Mousseau hopes their results, which are consistent with the "linear-no-threshold" model for radiation effects, will better inform the debate about exposure risks. "With the levels of contamination that we have seen as a result of nuclear power plants, especially in the past, and even as a result of Chernobyl and Fukushima and related accidents, there's an attempt in the industry to downplay the doses that the populations are getting, because maybe it's only one or two times beyond what is thought to be the natural background level," he said. "But they're assuming the natural background levels are fine." "And the truth is, if we see effects at these low levels, then we have to be thinking differently about how we develop regulations for exposures, and especially intentional exposures to populations, like the emissions from nuclear power plants, medical procedures, and even some x-ray machines at airports." 【313】
【计时三】
Men and Women Battle for Ideal Height: Evidence of an Intralocus Sexual Conflict Currently Raging in Human DNA
ScienceDaily (Nov. 13, 2012) — A battle about the ideal height would appear to be raging in men's and women's genes. Gert Stulp, PhD candidate at the University of Groningen, has shown that this conflict is leading to a difference in reproductive success between men and women of varying height. [attachimg=300,424]109823[/attachimg]
"Natural selection is still occurring in human beings, despite birth control and good medical facilities," says Gert Stulp. Together with colleagues from Groningen, Amsterdam and Cambridge (UK), he managed to find evidence of an intralocus sexual conflict currently raging in the DNA of the human race. "A conflict like this arises because men and women are different and therefore subject to different selection pressures," explains Stulp. A stag, for example, benefits from big antlers, but they would be impractical for a doe. 'Nature has "switched off" antler development in does, so there is no conflict between the male and female animals. However, some of the traits that are helpful to one sex but a hindrance to the other cannot be quite so easily switched off." This is the case with height in human beings. Short parents tend to produce short daughters and short sons. This benefits the reproductive success of the daughters, but not that of the sons. 'We know that shorter women have more children than women of an average height. With men, this is the other way round.' As short women and men of average height have the most children, their genes are passed on the most. 【266】
【计时四】
This difference in selection pressures for human height between the sexes could mean that shorter families are more successful at reproducing via the women, while families of an average height produce more children via the men in the family. This is known as an intralocus sexual conflict: a particular trait (in this case: being short or of average height) is an advantage when it presents in one sex, but a disadvantage when it presents in the other. The question being addressed is whether this conflict can be demonstrated in humans. Stulp studied the number of children born to brothers and sisters in a large-scale American database containing data on thousands of residents of Wisconsin born in 1937 or 1938. "It turned out that by taking the height of just one individual/person, we could predict whether his or her sibling would produce many or few children. Shorter individuals have a higher chance of becoming an uncle or aunt through their sister, while individuals of average height are more likely to have nephews and nieces via their brother." The sexual conflict relating to body height was clearly visible. "We are the first researchers to actually demonstrate this type of genetic conflict in humans." It is still unclear why shorter women have more children. "A conflict between growth and reproduction is common in some species of animals," continues Stulp. Short women probably put more energy into reproducing. "In general, the earlier a woman has her first child, the more children she will have. Women with a genetic tendency to have children at a young age also appear to have a genetic tendency to be short. But whatever the reason, evolutionary processes still seem to be alive and kicking in modern society." 【288】
【计时五】
Warming Temperatures Will Change Greenland's Face, Experts Predict
ScienceDaily (Nov. 13, 2012) — Global climate models abound. What is harder to pin down, however, is how a warmer global temperature might affect any specific region on Earth. [attachimg=300,207]109824[/attachimg]
Dr. Marco Tedesco, associate professor of earth and atmospheric sciences at The City College of New York, and a colleague have made the global local. Using a regional climate model and the output of three global climate models, they can predict how different greenhouse gas scenarios would change the face of Greenland over the next century and how this would impact sea level rise. The resulting fine-scale model gives a high-resolution picture of the island's future. "We put Greenland under a microscope to see what accounts for melting and for ice mass changes in different regions," said Professor Tedesco. He and his colleague, Xavier Fettweis of the University of Liege, Belgium, reported their results online November 8 in Environmental Research Letters. They compared two possible future CO2 scenarios: a concentration of carbon dioxide in the atmosphere projected for the end of the century of 850 parts per million (ppm) versus a more aggressive projection of 1370 ppm. The first approximates the current rate of increase. The Greenland ice sheet would lose more ice and snow to melting than it would accumulate in both scenarios. Basins on the southwest and north coasts would suffer the greatest losses. Temperatures would only have to increase by 0.6 to 2.16 degrees Celsius (1.8-3.9 ° F) to tip the balance into more loss than gain. The new model shows how a melting would alter the topography of "one of the world's refrigerators," potentially affecting adjacent ocean circulation and salinity, and speeding further melting. Though dramatic, Professor Tedesco said the predictions he reported might be too conservative. "They don't take into account progressive effects of the changing elevations and topography and the acceleration of ice sheet movement." These results, however, represent a step forward toward understanding the potential repercussions of warming temperatures; an improvement on models that give a much coarser view into the future, he added. "Some areas will be 400 meters below the current elevation just because of melting. This might very well impact the speed and amount of ice that is flowing to the ocean. It would increase the rate of melting, because conditions get warmer at lower elevations" he noted. "Imagine an ice cream that is melting much faster in one area. This will change the shape of the ice mass over Greenland." 【417】
【越障】
Solving the Mystery of Aging: Longevity Gene Makes Hydra Immortal and Humans Grow Older
ScienceDaily (Nov. 13, 2012) — Why do we get older? When do we die and why? Is there a life without aging? For centuries, science has been fascinated by these questions. Now researchers from Kiel (Germany) have examined why the polyp Hydra is immortal -- and unexpectedly discovered a link to aging in humans. [attachimg=399,340]109825[/attachimg]
The study carried out by Kiel University together with the University Medical Center Schleswig-Holstein (UKSH) will be published this week in the Proceedings of the National Academy of Sciences (PNAS). Hydra -- mysteriously immortal The tiny freshwater polyp Hydra does not show any signs of aging and is potentially immortal. There is a rather simple biological explanation for this: these animals exclusively reproduce by budding rather than by mating. A prerequisite for such vegetative-only reproduction is that each polyp contains stem cells capable of continuous proliferation. Without these stem cells, the animals could not reproduce any more. Due to its immortality, Hydra has been the subject of many studies regarding aging processes for several years. Aging in humans When people get older, more and more of their stem cells lose the ability to proliferate and thus to form new cells. aging tissue cannot regenerate any more, which is why for example muscles decline. Elderly people tend to feel weaker because their heart muscles are affected by this aging process as well. If it were possible to influence these aging processes, humans could feel physically better for much longer. Studying animal tissue such as those of Hydra -- an animal full of active stem cells during all its life -- may deliver valuable insight into stem cell aging as such. Human longevity gene discovered in Hydra "Surprisingly, our search for the gene that causes Hydra to be immortal led us to the so-called FoxO gene," says Anna-Marei Böhm, PhD student and first author of the study. The FoxO gene exists in all animals and humans and has been known for years. However, until now it was not known why human stem cells become fewer and inactive with increasing age, which biochemical mechanisms are involved and if FoxO played a role in aging. In order to find the gene, the research group isolated Hydra's stem cells and then screened all of their genes. Immortality mechanism of Hydra revealed The Kiel research team examined FoxO in several genetically modified polyps: Hydra with normal FoxO, with inactive FoxO and with enhanced FoxO. The scientists were able to show that animals without FoxO possess significantly fewer stem cells. Interestingly, the immune system in animals with inactive FoxO also changes drastically. "Drastic changes of the immune system similar to those observed in Hydra are also known from elderly humans," explains Philip Rosenstiel of the Institute of Clinical Molecular Biology at UKSH, whose research group contributed to the study. FoxO makes human life longer, too "Our research group demonstrated for the first time that there is a direct link between the FoxO gene and aging," says Thomas Bosch from the Zoological Institute of Kiel University, who led the Hydra study. Bosch continues: "FoxO has been found to be particularly active in centenarians -- people older than one hundred years -- which is why we believe that FoxO plays a key role in aging -- not only in Hydra but also in humans." However, the hypothesis cannot be verified on humans, as this would require a genetic manipulation of humans. Bosch stresses however that the current results are still a big step forward in explaining how humans age. Therefore the next step must be to study how the longevity gene FoxO works in Hydra, and how environmental factors influence FoxO activity. Without stem cells we all die Scientifically, the study has two major conclusions: On the one hand it confirms that the FoxO gene plays a decisive role in the maintenance of stem cells. It thus determines the life span of animals -- from cnidarians to humans. On the other hand, the study shows that aging and longevity of organisms really depend on two factors: the maintenance of stem cells and the maintenance of a functioning immune system. 【697】
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