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宁德治疗男性精子大约多少钱福州市宫腔镜手术哪家医院好Science and Technology科学技术Palaeontology古生物学Splay-footed, not flat-footed八字足,而非平足A new fossil shows that evolution does not always mean change一个新的化石表明:进化并不总是意味着改变Then and now过去与现在WHEN a coelacanth, a type of lobe-finned fish once considered the missing link between fish and amphibians, was found off the coast of South Africa in 1938, it came as a shock to palaeontologists.以前人们一度认为一种叫做腔棘鱼的鳍鱼是鱼类和两栖类之间缺少的环节,1938年当腔棘鱼在南非海岸沿海被发现时,古生物学家对它的出现大感震惊。Until then, the most recent traces of such a creature had been in rocks dating from the last days of the dinosaurs, 65m years ago.在此之前,这种动物最近的遗迹出现在6500万年前恐龙时代后期的岩层中。It was, in its way, as surprising as if a live Tyrannosaurus had been found hiding in an obscure part of Montana.而它这次的出现方式,就好像一个活生生的霸王龙属被发现藏身在蒙大拿州的模糊地带一样令人惊讶。Now the same experience is hitting palaeontologists again—but this time in reverse. Instead of finding a living fossil identical to an ancient beast, they have found a real fossil identical to a modern one.现在,同样的经历再次让古生物学家碰上了,不过这次相反。他们不是找到了一个与古兽相同的活化石”,而是找到了一个跟现代兽类相同的真正化石。The fossil in question, a 100m-year-old specimen from north-east Brazil, belongs to the genus Schizodactylus.所讨论的的化石采自巴西东北部,是一亿年前的标本,属于节肢动物类。These are large, carnivorous, cricket-like insects whose feet splay out wildly in different directions.这类节肢动物是大型类似板球的食肉昆虫,其足向不同方向伸展开来。Modern Schizodactylus use their feet like snowshoes, to help them remain stable as they travel over sandy terrain in search of prey.现代节肢动物在沙地爬行寻找猎物时用它们雪鞋般的脚来帮助身体保持稳定。If the new fossil—whose discovery has just been published in ZooKeys by Sam Heads of the Illinois Natural History Survey and Léa Leuzinger of the University of Fribourg, in Switzerland—were merely similar to modern splay-footed insects, the find would not be particularly surprising:如果新化石其发现刚由伊利诺斯州自然史调查的负责人山姆和瑞士弗里堡大学的李?劳伊辛格发表在《动物图谱》上仅是类似现代的八字足昆虫,那么这个发现不会特别令人惊讶:it simply demonstrates a phenomenon called evolutionary stasis, in which a specific type of body form hangs around for a long time.它只是明了一种被称为进化停滞的现象,在这种现象中特定类型的体型存留很长一段时间了。What is surprising is just how static Schizodactylus has been.令人惊讶的是节肢动物停止进化竟有这么久了。Evolutionary stasis is fairly common at the higher levels of the Linnaean system of biological classification.在林耐生物分类系统的高等类别中进化停滞现象是相当普遍的。Natural selection hits on a good design.自然选择的图案都是最好的。That design is then adopted in slightly different forms by species after species.然后,这种图案就被一个接一个的物种以略有不同的形式所采纳。The shelled bodies of turtles, for example, evolved between 250m and 200m years ago, while the body plans of scorpions have been around for more than 400m years.例如,海龟的壳体是在2.5~2.0亿年前进化的,而蝎子的体型方案已超过4亿年的历史。That does not mean, however, that a zoologist would mistake a 200m-year-old turtle or a 400m-year-old scorpion for any species now alive.然而这并不意味着一个动物学家会弄错2亿岁的海龟或是4亿岁的蝎子属于现在存活的何种物种。What is remarkable about the new find is that it is so similar to modern animals that it can be assigned to an existing genus—the lowest level of Linnaean classification above a species—rather than just to some higher taxonomic group.新发现引人注目的是它与现代动物如此相似,以致它可以被列入现有生物分类种类,而不是只被列入某一更高等的分类组。That is rare indeed.这的确罕见。Even the modern coelacanth, on closer examination, had to be put in a different genus from any known fossil.经过仔细观察,甚至就连现代腔棘鱼都必须得归类于不同于任何已知化石的种类。Clearly the body plan of Schizodactylus is not merely good, but optimal, at least for the environment the animal lives in.显然,节肢动物的体型方案不仅是最好的,也是最佳的,至少对这种动物生活的环境而言是如此。Alas for Schizodactylus, the sandy deserts it prefers have retreated from north-eastern Brazil and its optimality there has vanished.唉,对节肢动物来说,它所喜爱的沙质沙漠已经从巴西东北部退却,它在那里的最佳体态已经消失。But its discovery shows better what this part of the world was like 100m years ago—and also illustrates an important point about evolution that is often forgotten in biologists understandable focus on the development of novelty. The first rule of natural selection is: If it aint broke, dont fix it.”但它的发现恰好说明这部分的大千世界跟1亿年前的样子很象,也说明了进化论的一个重点,而这点在生物学家关注理解新颖性的发展时往往被遗忘了。自然选择的第一条规则是:如果没坏,就不要修理它。” 点击此处下载本期经济学人讲解PDF与音频字幕 /201303/228974福州那间医院男科精子检查比较好 Science and Technology Epigenetics and stress Baby blues科技 外因遗传与压力 新生儿蓝调曲A mothers stress while she is pregnant can have a long-lasting effect on her childrens genes母亲期压力过大会对孩子的基因造成长期影响RESEARCHERS have known for years that children whose mothers were chronically stressed during pregnancy—by famine, anxiety, the death of a relative or marital discord, for instance—show higher-than-normal rates of various psychological and behavioural disorders when they are adults.研究人员多年前就发现,如果母亲在怀期间长期遭受因饥饿,焦虑,亲友死亡或婚姻不幸等引起的过大压力,她们的孩子成年后出现各种心理疾病和行为问题的几率会高于平均几率。They have also known for a long time that those brought up in abusive environments often turn out to be abusive themselves.研究人员也早知道,在受虐环境下成长起来的孩子长大后往往本身也有施虐倾向。The second of these observations is usually put down to learning.The reason for the first has remained unclear. 人们通常把后面的这个发现归咎于盲目效仿,而头一个发现的原因却仍旧模糊不清。A study just published by Axel Meyer, Thomas Elbert and their colleagues at the University of Konstanz in Germany, however, points to a phenomenon called epigenetics as the likely answer.然而,德国康士坦茨大学的Axel Meyer, Thomas Elbert以及他们的同侪们最近发表的研究报告指出,一种被称为;外因遗传;的现象很有可能就是这个问题的。And if Drs Meyer and Elbert are right, it also suggests an alternative explanation for the inheritance of abusiveness.如果Meyer和Elbert士的结论是正确的,那它也为施虐遗传现象做出了另一个解释。Epigenetics is a type of gene regulation that can be passed from a cell to its daughters. The most common mechanism is methylation.外因遗传是一种可以传给下一代细胞的基因调控过程,This attaches methyl groups (a carbon atom and three hydrogens) to either adenine or cytosine,最常见的方式是通过甲基化作用来完成,该作用可以让甲基(由一个碳原子和三个氢原子组成)附着于腺嘌呤或胞嘧啶上。two of the four chemical bases that form the alphabet of DNA, depending on the gene involved.腺嘌呤和胞嘧啶是DNA四大成分其中之二,而到底附着于哪一个则取决于具体的基因。The consequence is to inactivate the gene being methylated.甲基化作用将使甲基化的基因失去活性。In the case of stress, previous studies have suggested that methylation of the gene which encodes glucocorticoid receptors is important.以往的研究表明,当母亲压力过大时,负责为糖皮质激素受体编码的基因的甲基化具有重要意义。Glucocorticoid receptors relay signals from stress hormones in the blood into cells.糖皮质激素受体依靠血液中的压力激素发出信号而进入细胞。In particular, they do so in those regions of the brain that control behaviour.尤其值得注意的是,这个过程在大脑中控制人体行为的区域进行。Newborns whose mothers suffered from depression while they were pregnant are known to have more highly methylated glucocorticoid-receptor genes than others.新生儿的母亲若是在怀期间出现抑郁症状,他们糖皮质激素受体基因的甲基化程度就会比其他新生儿更高。The same is true of children who were abused when young.幼时受虐的孩子在这一点上也有相同表现。In infants, the level of glucocorticoid-receptor methylation is correlated with the release, in response to stress, of higher-than-normal amounts of stress hormones.胎儿糖皮质激素的甲基化程度与人体抑郁时分泌过多的压力激素有关。And in rats, such methylation makes young animals especially sensitive to stress, and also fearful of novelty.而老鼠试验表明,这样的甲基化过程让幼小动物对压力尤其敏感,对新鲜事物也感到恐惧。What has been unclear until now, however, is how long such effects persist.然而,现在还没弄清楚的是,这样的效应会持续多久。Dr Meyers and Dr Elberts study, published in Translational Psychiatry, offers a clue.Meyer士和Elbert士在《转化精神病学》杂志中发表的研究报告给出了。Troubled teens问题青少年Their team examined the methylation of the glucocorticoid-receptor gene in a group of children ranging in age from ten to 19 years, and in those childrens mothers. The researchers also used a psychological survey to try to determine which of the mothers had been physically or psychologically abused before, during or after pregnancy.他们的研究小组对一组年龄从10岁到19岁不等的青少年以及他们母亲体内糖皮质激素受体基因的甲基化程度进行了测量,还通过心理测试试着找出哪些母亲在期中或者生产后曾遭到身体或者心理上的虐待。They found that women abused during pregnancy were significantly more likely than others to have a child with methylated glucocorticoid-receptor genes.研究发现,期中遭到虐待的母亲生下糖皮质激素受体基因被甲基化的幼儿的可能性要比其他母亲高出得多。By contrast, abuse before or after pregnancy resulted in no such correlation. Nor was the mothers own methylation affected by violence towards her.相反,在前或是生产后遭到虐待的母亲则不会生下这样的幼儿,而且她们本身基因的甲基化与否也跟是否遭到家庭暴力无关。Taken together, these results suggest that glucocorticoid-receptor-gene methylation happens in the fetus in response to a mothers stress, and persists into adolescence.总体看来,这些结论表明胎儿糖皮质激素受体基因的甲基化是由于母亲压力过大引起的,并且其影响将会持续到青春期。This has implications for those adolescents long-term health.这会影响青春期孩子的长期健康。Dampened glucocorticoid-receptor-gene activity has been shown to increase the risk of obesity, of depression and of some autoimmune diseases. It also makes people more impulsive and aggressive—and therefore,事实明,糖皮质激素受体基因不够活跃会增加孩子患肥胖症,抑郁症以及某些免疫系统疾病的风险,也会让他们成年后个性更加冲动,更加富有侵略性。if male, more likely to abuse the pregnant mothers of their children, thus perpetuating the whole sorry cycle.因此,如果孩子是男性,他们更有可能施虐于怀着自己孩子的待产妇女,从而造成持续的恶性循环。Why, in light of such negative effects, have humans evolved to be programmed this way while still in the womb?发现了这种消极效应后,科学家们不禁问道,为何人类还在子宫内的时候就被设立了这样的一个进化程序呢?Part of the answer is probably that not all the negative consequences would have shown up at the time the mechanism was evolving.也许部分原因是,当甲基化作用还在进化的时候所有的消极影响不会当即全部表现出来。Obesity, for example, is rare in a state of nature.例如肥胖症在极少数情况下是天生的。The other part is that some of the consequences probably have a positive effect.还有一个原因是,部分消极影响也许会带来积极效应。If a mother lives in an environment where fear-inducing experiences are common, say, giving her offspring a sensitivity to fear may be no bad thing.如果母亲生活在一个很容易产生害怕心理的环境里,那么让她的后代对害怕情绪敏感也许并不是坏事。What can be done with such knowledge is unclear.知道了这些真相对人们有什么意义尚不明确。Drugs that demethylate DNA are under development, but are still some way from approval—and, in any case, interfering with epigenetics, which is a widesp mechanism of gene regulation, is a drastic approach.让DNA反甲基化的药物还在研发中,并且还未通过临床明。另外,外因遗传是基因调控的常见手段。从任何角度来说,干预外因遗传都是一种极端激进的做法。The research might, though, point to the period when intervening to stop abuse will have the greatest effect.但这项研究也许会把科学家们引向另一个方向,那就是找出对基因调控进行干涉从而阻止家庭暴力的最有效时期。Then again, such intervention is always desirable, for the sake of both mother and child.为了让母亲和孩子们都幸福,这样的干涉乃众望所归。 /201211/210685As North America emerged from the grip of the last ice age, the door was opened to outsiders for the very first time.自从冰川时期末期开始,人们开始第一次踏上北美大陆。As these early immigrants pushed their way south, they found themselves in a land of an unimaginable opportunity, overflowing with game mammals, animals with no experience of humans or their weapons.当这些早期移民向南迁移时,他们发现自己脚下的这片土地拥有难以想象的机会,到处都是哺乳动物,这些动物没有和拿着武器的人类相处过。The arrival of these hunters coincided with a time of great change of the plains.随着猎人的到来,这个广袤的平原也迎来大变化的时期。Within the next few hundred/ years, many ice age animals vanished forever.在接下来的数百年,许多冰河期动物永远消失了。So 13,000 years on, how do we know anything about this lost world? There are still clues to be found if you know where to look.所以13000年过去了,我们怎么知道有关那个过去世界的一切?如果你想知道,还需要继续探索。In the Bighorn Mountains of Wyoming is a hidden cave recreated here, where over the millennia thousands of animals have fallen to their death.在怀俄明州的大角山是重建的一个隐秘的山洞,成千上万的动物在这里摔死。Preserved below the surface are bones dating all the way back to the ice age.表面之下的骨头可以追溯到冰河世纪。Remains of bison lie alongside antelope and rabbit.野牛的尸体躺在羚羊和兔子旁边。But they are mixed with those of camels, extinct horses, giant wolves.和他们混在一起还有骆驼、灭绝了的马和巨型的狼。201303/230191福州做多囊卵巢手术最好三甲医院

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福建看早泄那家医院最好 In the 80s, a talking car like knight riders kit was pure fiction.80年代的电影《霹雳游侠》中会说话的汽车只是科幻故事。;My electronic sensors picked up a destination signal...;“我的电子传感器收到目标地点信号……”Not anymore. Modern cars are really computers on wheels. ;You often hear the es about how they are more advanced than the space machinary that got us to the moon, back in the 1960s and 1970s. And thats true.;现在,智能汽车不再只是幻想。现代汽车正是电脑和车轮的组合。“在20世纪60,70年代,你总是听到人们幻想智能车比登月的设施还先进,现在成真了。”It takes just one look under the hood to see for yourself. Compare the machinary of this 1966 Ford, Mustang, to this, 2004 Volkswagen, Jetta.你只需要掀开引擎盖看一眼,比较一下66年的福特野马和04年的大众捷达便知。;Almost everything in a car relies on a computer, one kind or another now. You have the engine control monitor which controls the engine functions, the cooling fan, everything under the hood pretty much.;“现在,几乎车内的一切设施都依赖于电脑系统,电脑控制引擎,监控设备,冷气扇……几乎涉及引擎盖下的一切”Mechanics say the more they are computerized, the easier they are to fix. Sometimes, they even fix themselves. ;So the computer can sometimes be a little too helpful?;电脑控制得越彻底,车辆就越容易修理。有时电脑对自身能进行自动修理。“因此,有时候电脑也过于有用了?”;Yes, exactly. you still have to do your maintance, you still have to check. Follow the manual about things that have to be changed in certain specific intervals.;“是的,没错。你还是需要对爱车进行日常护理,检查。定期对车辆进行手动检查。”But what about when things go wrong with the ultra-computer itself?但如果是电脑系统出问题了呢?;There is nobody, no person to point to who designs the electronic system. There are multiple people in multiple teams all coordinating their efforts to design any different part of the vehicle.;“没人能说出是谁在汽车中设计使用了电子系统。是不同研究小组的不同人员共同向着这同一个目标努力,并设计出汽车的不同零部件。”Some experts foresee the day when cars such as those in the moviedrive themselves.许多专家都预见无人驾驶的智能汽车问世的一天。;What kind of risks will it involve and will we see any fallout from that.;“智能汽车将带来怎样的风险,会有什么附加后果呢?”The key they say is for drivers to remember who is behind the wheel. And act that way no matter how advanced the car.避免智能车带来的负面影响只需要一点,就是驾驶者无论爱车有多先进,要始终牢记得坐在车子里面的是人,不管怎样都要爱惜生命。Diana Alvear, A news, Chicago.Diana Alvear芝加哥报道,A新闻注:本篇文章英文来自普特论坛,译文属原创,,。201207/191661福州省人民医院治子宫粘连费用福州输卵管复通术去哪里

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