人类基因数量为什么比估计的少3/4?艾滋病疫苗永远都不会成功吗?
关于宇宙、关于地球、关于我们自身，有太多的谜题等待我们去挖掘。但哪些是最重要的未解之谜，我们距离找到答案还有多远?今年7月1日，在纪念美国《科学》杂志创刊125周年之际，科学家们总结出了125个迄今我们还不能很好回答的问题，重中之重有25个。
宇宙篇:
1、宇宙是由什么组成的?
一个脱口而出的答案是:由那些亮晶晶的星星组成的。但在最近几十年中，科学家越来越发现这个答案是不正确的。天文学家认为，组成恒星、行星、星系——当然还有我们——的物质，或者叫普通物质，只占宇宙总质量的不到5%。他们估计，另外25%，可能是由尚未发现的粒子组成的暗物质。剩下的70%呢?天文学家认为那可能是暗能量——让宇宙加速膨胀的力量。暗物质和暗能量的本质是什么?科学家正在用加速器和望远镜寻找这些问题的答案，如果找到了，其意义肯定是宇宙级的。
2、我们在宇宙中是唯一的吗?
45年前，天文学家弗克·德雷克首次启动了探寻地外文明的奥兹玛计划——用巨大的天线(射电望远镜)接受外星文明发射的信号。45年过去了，天文学家的努力仍然在继续着。然而，即使是迄今为止规模最大的“凤凰”计划，也还没有找到任何来自外星文明的无线电信号。
地球篇:
3、地球内部如何运作?
40多年以前，一场地球科学的革命发生了。板块构造学说更新了关于地球自身的知识。但是关于地球内部构造的问题，仍然沿袭着革命之前的知识。科学家在这40年中所做的，就是把这个鸡蛋模型——分为地壳、地幔和地核进一步细化。借助于越来越先进的地震波成像技术，科学家正在研究地球这个庞大机器的运作过程。但是要掀起另一场科学革命，可能还需要半个世纪。
4、地球温室将变得多热?
尽管大气的二氧化碳浓度肯定会在这个世纪继续增加，尽管这种增加肯定会带来全球变暖，但是变暖的程度仍然不太确定。科学家一般认为，这个世纪二氧化碳浓度的加倍会带来1.5℃～4.5℃的升温。但是这不够精确。科学家正在发展新的数学模型，试图让数字更令人信服。
数理化篇:
5、物理学定律可以被统一起来吗?
苹果落向地面、一道闪电划过长空、核电站反应堆里的铀原子衰变同时放出能量，超级加速器击碎质子:这几种现象代表着自然界中四种基本力的作用，也就是引力、电磁力、弱力和强力。宇宙间所有的物理现象都可以用这四种基本力进行解释。但是科学家并不满足。有没有可能把这四种力统一成为一种?上个世纪60年代，物理学家发现弱力和电磁力是可以统一起来的，它们是一种事物的不同侧面，统称电弱力。但是其余两种力是否可以和它统一起来?
6、在量子不确定性和非定域性之下，还有更深层次的原理吗?
量子理论已经诞生了100年有余，它产生了令人信服的应用成果，但是它也带来了反直觉:量子力学的不确定原理指出我们无法同时精确地获得一个物体的动量和位置。而非定域性让两个处于量子纠缠态的粒子的纠缠态同时崩溃，而不管它们相距多远。爱因斯坦就说过，尽管量子力学给他留下了非常深刻的印象，但是“一个内心的声音告诉我，它还不是真实的东西。”
7、我们能把化学自我装配推进多远?
在某种意义上，化学家是最喜欢发明的一群人，因为他们总是不断制造出新型的分子。尽管今天的化学家已经能制造出很复杂的化学结构，他们能让这项工作变得既简单又复杂吗?也就是说，让“原料”原子自己“装配”成复杂的结构，就像生命所表现出来的那种自我装配的特性。已经有一些化学自我装配的实例，例如制造类似细胞膜的双层膜结构。但是更高级的自我装配，例如自下而上地制造集成电路，仍然是一个梦想。
8、传统计算的极限是什么?
有些事看上去很简单但是解决起来很复杂，例如一个推销员要走遍相互连接的几个城市，那么怎样走才能实现总路程最近?城市数量的增加会让最强大的电子计算机也感到畏惧。上个世纪40年代，信息论之父香农提出了信息(以比特方式存在)储存和传递所遵循的物理规律。任何传统的计算机都不能超越这个规律。那么，在工程上，最终我们能造出多么强大的计算机?不过，非传统的计算机可能并不受到这些限制，例如近年来兴起的量子计算机。
生物篇:
9、意识的生物学基础是什么?
17世纪的法国哲学家有一句名言:“我思故我在”。可以看出，意识在很长时间里都是哲学讨论的话题。现代科学认为，意识是从大脑中数以亿计的神经元的协作中涌现出来的。但是这仍然太笼统了，具体来说，神经元是如何产生意识的?近年来，科学家已经找到了一些可以对这个最主观和最个人的事物进行客观研究的方法和工具，并且借助大脑损伤的病人，科学家得以一窥意识的奥秘。除了要弄清意识的具体运作方式，科学家还想知道一个更深层次问题的答案:它为什么存在，它是如何起源的?
10、什么控制着器官再生?
有一些生物拥有非凡的修复本领:被切断的蚯蚓可以重新长出一半身体，而蝾螈可以重建受损的四肢……相比而言，人类的再生本领似乎就差了一点。没有人可以重新长出手指，骨头的使用也是从一而终。稍可令人安慰的是肝脏。被部分切除的肝脏可以恢复到原来的状态。科学家发现，那些可以让器官再生的动物，在必要的时候重新启动了胚胎发育时期的遗传程序，从而长出了新的器官。那么人类是否可以利用类似的手法，在人工控制下自我更换零部件呢?
11、一个皮肤细胞如何能变成神经细胞?
在上个世纪中期，生物学家把青蛙的体细胞核放入青蛙的去核卵细胞里，结果制造出了克隆蝌蚪。最近几年，关于人类胚胎干细胞的研究正在热火朝天地进行——把人的体细胞核放入卵细胞中，科学家期待着制造出各种各样的人类体细胞，例如神经细胞、成骨细胞、心肌细胞等等。尽管科学家已经取得了一些成功，他们仍然对于这种体细胞核移植技术能够成功的原因知之甚少。的确，去核的卵细胞在这个过程中扮演着至关重要的角色——可是具体机制是什么?
12、一个体细胞是如何变成整株植物的?
在某种意义上，植物似乎比动物有更大的灵活性。植物的体细胞不需要繁琐的体细胞核移植技术，就能重新变成植物胚胎细胞。科学家很早就已经开始利用植物的这种性质。用一小块植物组织，在实验室里就能培养出可以供一片森林使用的幼苗。但是为什么植物细胞有这样的灵活性?科学家已经发现了一些线索，例如植物的生长素在这个过程中起到的作用。
13、生命是如何以及在哪里起源的?
科学家已经发现了34亿年前的微生物的化石，在更古老的岩石上也能找到生物光合作用的痕迹。那么蛋白质和DNA——生命的两大支柱——哪一个先出现在地球上?或者一起出现?科学家认为，更可能的情况是，RNA比前两者更早出现。另一个问题是，生命在什么样的环境下起源?一种假说认为，生命最早起源于海底的热水中。如今，科学家一方面在实验室里探寻从简单有机物到可以自我复制的有机物的发展过程，另一方面，研究彗星和火星，也将为这个问题带来重要的启示。
14、什么决定了物种多样性?
这是一个充满生命的行星，但是并非每一个角落的生命都同样繁荣。一些地区居住的物种的数量超过其他地区。热带比寒带拥有更高的物种多样性。为什么会出现这种情况?仅仅是因为热带比寒带更热?科学家认为，生物和环境之间的相互作用对多样性起着关键的作用。当然，还有其他一些改变多样性的力量，例如捕食和被捕食的关系。但是，科学家首先面临的问题是如何获取关于全球物种多样性的基础数据——到底有多少种生物在那儿。
15、合作的行为如何进化?
你很容易在社会性动物身上看到利他的行为。例如蜜蜂把食物的信息传递给其他蜜蜂。人类和其他灵长类动物社会也充满了合作的行为。进化论的创立者达尔文对合作现象提出过一些解释，例如亲属之间的相互帮助，实际上会促进整个家族繁殖的可能性。如今，科学家正在寻找合作行为的遗传基础。而博弈论——一种关于竞争、合作和游戏规则的数学理论，也能够帮助科学家理解合作行为如何运作。达尔文观察到了合作的现象并做出了解释，今天的科学家希望能够让这个解释更加深入，并且希望能够回答它是如何产生的。
16、如何从大量的生物学数据中得到全景?
生命是如此的复杂，以至于几乎每一位生物学家都只能在一个很小的领域进行探索。尽管在每一个领域都产生了大量的描述性的数据。但是科学家能够从这些海量的数据中得出一个整体的概念，例如生物是如何运作的?系统生物学这门正在形成的学科为回答这些问题提供了一些希望。它试图把生物学的各个分支联系起来，利用数学、工程和计算机科学的方法让生物学更加量化。不过，现在还没有人知道这些方法是否能够最终让科学家理解生物运作的整体图景。
人类篇:
17、为什么人类的基因这么少?
2003年，当人类基因组计划接近完成的时候，生物学家在欢呼这一成就的同时，惊奇地发现人类的基因数量比原先估计的少，是的，人只有大约2.5万个，而原来认为应该有10万个。相比之下，一种非常简单的生物——线虫也有2万个基因。拟南芥植物的基因数量比人类稍多，而水稻的基因数量则是人类的一倍。科学家认为，基因组运作的方式应该比以前认为的更加灵活和复杂，他们正在探寻这些少用基因多办事的分子机制。
18、遗传差异和个体健康在多大程度上是相关联的?
很早以前科学家就发现有些人对于某些药物的反应和其他病人不同。例如，某种麻醉用肌肉松弛剂会导致特定的人无法呼吸，最终，科学家发现这种现象的原因在于他们拥有特定的基因。这也就带来了一个问题:研究不同的人之间的遗传差异是否可以促进医学发展出更高级的治疗手段，也就是说，根据个人的DNA进行“量体裁药”?科学家已经辨认出了一批与药物相互作用的基因。但是要真正实现“量体裁药”，恐怕还为时尚早。
19、人类寿命可以延长多少?
尽管百岁老人仍然少见，人类的平均寿命(尤其是在发达国家)在过去的几十年中一直在延长。但是这种趋势能保持多久?科学家通过对实验动物的研究，发现包括限制热量摄入在内的一些方法可以显著地延长它们的寿命。但是这些方法是否可以成功地应用到人类的身上，以及能延长多少寿命呢?一些科学家认为，至少人类活到100岁可以成为家常便饭。不过，即使是这样，长寿也会带来其他的麻烦，比如社会保险。
20、什么遗传差异导致我们成为独特的人类?
随着基因测序技术的改进，越来越多物种的基因组全序列进入了科学家的数据库中，包括我们自己和数种灵长类亲戚，比如黑猩猩。我们很容易分辨出人和黑猩猩，然而在分子水平上，这种分辨却不那么容易。我们和黑猩猩的DNA差异大约是1.2%。这是一个很小的数字，但是从绝对数量上来看，这种差异意味着3千多万个碱基对的不同。到底是这3千多万个差异中的哪些，让我们在与黑猩猩“分家”之后，变得如此独特?科学家正在寻找那些让我们有别于其他灵长类物种的遗传差异，当然，还有文化、语言和技术等等超越基因的因素。
21、记忆是如何存取的?美好的记忆、悲伤的记忆，关于解方程技巧的记忆，英语单词的记忆，毫无疑问它们都储存在我们的大脑中。但是它们具体在什么部位?
上个世纪50年代，科学家发现大脑中的“海马区”在存储信息的过程中扮演着至关重要的角色——如果切除掉海马区，那么以前的记忆就会一同消失。但是海马区的神经细胞如何把信息固定下来?科学家发现一些分子参与到了记忆的形成。此外，神经细胞突触地形成也与记忆相关联。但是，科学家目前对于记忆的运作机制的了解还不够——而这一机制对于理解我们自身是非常重要的。
22、我们可以选择性地关闭一些免疫应答吗?
在今天，器官移植已经成为了一种不那么罕见的手术，但是医生和病人面对的一个大麻烦在一定程度上仍然存在:免疫排斥反应。病人的免疫系统有可能把移植的器官当作“非我族类”进行攻击，让手术功亏一篑。为了防止这种情况发生，医生要仔细挑选供体器官，而有的病人需要终身服用免疫抑制类药物——这显然不是个好主意。科学家已经找到了几种可能的方法，既让免疫系统正常工作，又不会排斥移植的器官的方法，但是要实现临床的应用，还需要很长的时间。
23、是否存在行之有效的艾滋病疫苗?
每年，仅仅美国国立卫生院就投入5亿美元用于艾滋病疫苗的研发工作。但是迄今为止还没有一种疫苗表现出实用性。怀疑者认为艾滋病疫苗永远都不会成功，因为人类免疫缺陷病毒(HIV)变化多端。而支持者认为，在猿免疫缺陷病毒上，疫苗可以产生效果，因此HIV的疫苗也可能成功。
24、什么能替代廉价的石油——以及什么时候?
没有人否认石油最终会用光。而且，石油产量可能不久就要开始下降。即便不考虑这些因素，全球变暖的危险也促使人类尽快找到替代石油的能源——太阳能?风能?核能?每一种似乎都很有潜力，但是它们都还不太成熟。
25、马尔萨斯仍然错了吗?
1798年，马尔萨斯发表了他著名的《人口原理》一书，他提出人口增长总是跟不上食品供应的增长，而只有灾难才能阻止增长。200年过去了，地球总人口增长到了60亿(是马尔萨斯时代的6倍)，但是马尔萨斯所预言的大灾难并没有发生。科学技术在很大程度上阻止了这种灾难。但是人类仍然面临着一个问题，如何保证大灾难不会在未来发生?
译文:
How much futher were we from the answers?——25 unsolved science problems
Why the number of human genes is 3/4 fewer than we originally estimated?Will it be never possible to find a vaccine against HIV?
About the universe,about the earth,about ourselves,there are too much problems for us to discover.But what are the most important ones?How much further were we from the answers?July 1st,in the celebration of the 125th anniversary of the American journal——"Science Magzine",scientists concluded 125 most compelling puzzles and questions which until now we have not been able to answer.the top 25 are most important.
Universe:
1.What is the universe made of?
Someone may bolt out:It's made up of the stars.But in the past several decades,scientists have come to find that wrong.Astronomers think mater,or what we call ordinary matter which makes up of the stars,planets,galaxies and,of couse,us,makes up less than 5% of the total mass of the universe.And they estimate that the other 25% may be dark matter which is made of the particles that we have not yet found.Then,what about the 70% left?Astonomers say it may be dark energy——the force that lead to an accelerated cosmic expansion.What is the hypostasis of dark matter and dark energy?Scientists have been searching for the answers by using accelerator and astronomical telescope.And if the answer is finnally found,the significance is undoubtedly "universe-class".
2.Are we alone in the universe?
45 years ago astonomer Frank Drake launched the first project——Ozma Project,to search for extraterrestrial intelligence(SETI),using large antenna(Radio Telescope) to receive signals from alien civilization.Now 45 years have past,astronomers are still trying hard.But even Project Phoenix,the biggest-ever one,have not found any signals from alien civilization.
Earth:
3.How does earth's interior work?
More than 40 years ago,a revolution in earth science arose.Continental Drifts Theory renewed our knowledge about the earth.But the theory about earth's interior structure is the same as what it was before the revolution.What scientists have done is to complete the egg model,divided it into 3 parts——Crust,Mantle and Centrosphere.By using Seismic Wave Imaging,scientists are now studying on the process of the big machine's work.But maybe we'd have to wait half a century for another revolution.
4.How hot will the greenhouse earth be?
It's sure that the concentration of CO2 will continue to increase,and it's also sure that this increase will result in global warming,but the extent is still not sure.Scientists generally figure that the increase of CO2 in this century will cause a 1.5℃～4.5℃ temperature rise.But it's not precise enough.Scientists are establishing new math model,trying to make the numbers convincible.
Mathematics,Physics And Chemistry:
Can laws of physics be unified?
An apple drop,a lightning across the sky,uranium in the nuclear reactor of a nuclear power plant gives off its energy while disintegrating,super accelerator breaks proton:all these phenomenons represent four fundamental forces in nature——gravitation,electromagnetic force,weak force and strong force.All the physical phenomenons can be explained by using the four fundamental forces.But scientists are not satisfied.Is it possible to unify the four forces?In 1960s,physicists found that weak force and electromagnetic force can be unified,they are different sides of a same thing,we call it electroweak force.But can the other two left be unified together?
6.Do deeper principles underlie quantum uncertainty and nonlocality?
Quantum Theory is more than 100 years old,it has convincible application achievements,but it also brings a reverse intuition:the uncertainty principle pointed out that we can not obtain the momentum and position of an object with precision at the same time.And the nonlocality principle make it possible for the entangled states of two particles in emtanglement to collapse at the same time,no matter how far they are from each other."Quantum mechanics is very impressive," Albert Einstein wrote in 1926. "But an inner voice tells me that it is not yet the real thing."
7.How far can we push chemical self-assembly?
In some sense,chemists are the kind of people who like inventing most,because they always create new molecules.Although nowadays chemists are able to build very complex chemical structure,can they make the job easy and at the same time complicated?That is to say,let the material atoms self-assemble and form a complex structure,just like the kind of self-assembly that life shows.We have some practice now,such as build a double membrane structure like cell membrane.But for more complexity,for example,to build an integrate curcuit from the top down,is still a dream.
8.What are the limits of conventional computing?
There are something in this world that looks easy but hard to solve,for example,if a salesman needs to walk around several cities which connect each other,how can he find a shortest distance?The increase of the numbers of the city would frustrate even the biggest computer.In 40s of last century,Claude Shannon,the father of Information Theory,brought forward the physical laws followed by the information(in form of byte) storage and transmission.Never can a traditional computer go beyond the laws.So in engineering,how strong a computer can we finnally make?However,non-traditional computer may not be astricted by these laws,for example,the recently springing-up quantum computer.
Biology:
9.What is the biological basis of consciousness?
In the 17th century the French philosopher said:"Cogito, ergo sum(I think,therefore I am)".We can see,consciousness has been a philosophy topic for a long time.Modern science considers consciousness emerges from the cooperation of billions of neurons in the brain.But it's still too general.To be specific,how do these neurons give birth to consciousness?In recent years,scientists have found some methods and tools to study the most subjective and most personal subject in an impersonal way,and by observing the patients with cerebral lesion,they have been able to peek the arcanum of consciousness.Besides make clear the way consciousness actually operates,scientists want an answer of a deeper question:why does it exist,and how did it originate?
10.What controls organ regeneration?
Some creatures have amazing ability of self-repairing:a cutted fishworm can outgrow another half of it's body,and newt can rebuild it's injured limbs......By comparison,human's ablility of organ regeneration seems not that good.Nobody can outgrow a cutted finger,so are our bones.What comforts us a little is liver.A partial resected liver can recover to its initial state.Scientists found that those animals,which are able to regenerate their organ,restarted some genetic process of fetation as occasion requires,so they outgrow new organs.Then,in a similar way,is it possible for us human to regenerate our organs under control?
11.How can a skin cell become a nerve cell?
In the middle of last century,biologists put a somatic cell nucleus of a frog into an enucleated egg cell,then created a clone tadpole.In recent years,the research on human embryonic stem cell are undertaking in full swing——putting human somatic cell nucleuses into enucleated human egg cells,scientists expect to produce many kinds of human somatic cells,such as nerve cells,osteoblasts,myocardial cells and so on.Scientists have made some progress,but they still know little about the reason for the success of cell nuclear transfer technology.It's sure that enucleated egg cell plays an important role in the process——then,what is the concrete mechanism?
12.How does a single somatic cell become a whole plant?
In some sense,plants seem more flexible than animals to survive and reproduce.They don't need the complicated process of somatic cell nuclear transfer technique.Scientists have been already using this advantage.By using only a tiny piece of plant tissue,they can grow enough seedings for a forest.But why do plant cells have this kind of flexibility?Scientists have found some clues,for example the effect of auxin in the process.
13.How and where did life on earth arise?
Paleontologists have found fossils of microbes dating back at least 3.4 billion years,photosynthetic organisms were also found on even older rocks.So the two backbones of life——protein and DNA,which appears earlier on earth?A hypothesis considers that life originated from the hot water in deep sea.Now,on the one hand scientists are looking for a way to show the development process from simple organics to organics with the function of self-reproduction,on the other hand,their studying on comets and Mars,will also bring some significant enlightenments.
14.What determines spicies diversity?
This is a planet of countless lives,but not every corner of the world is filled with the same prosperity.Some places have more spicies than the others.Tropic zone shows a higher diversity than frigid zone.Why?Is it only because tropic zone has a higher temperature?Scientists presume,the key is the interaction between lives and the environment.Of course there are other forces to change the diversity,just like the relationship between preyer and prey.But,the chief problem scientists are facing is how to acquire the basic data of the diversity of the world——how many spicies are there on earth?
15.How did cooperative behavior evolve?
It's easy for you to find alruistic behaviors in social animals.For example,a bee would send out information of food to the other bees.Human society and societis of other primates are also full of cooperative behaviors.Founder of Revolutionism,Darwin have explained this behavior to some extent,for example,the cooperation between relations actually increase the possibility of reproduction of the whole family.Nowadays scientists are looking for genetic basis of cooperative behavior.And the game theory——a matematic theory about competition,cooperation and the rules,helps them understand how do cooperative behaviors work.Darwin had once observed this kind of behavior and explained it,but contemporary scientists want a deeper explanation,and hope it would be able to explain how does this kind of behavior originate.
16.How will big picture emerge from a sea of biological data?
Lives are so complex that almost every biologist can only work in a small field.Although each field brings lots of descriptive datum,scientists have been able to form a general idea from them,such as how do lives operate?System biology,which is being forming nowadays,are offering some opportunities to answer these questions.System biology tries to combine the branches of biology and,by using mathematics,engineering and computing science,make biology more quantitative.But no one is sure that these methods can help biologists understand the big picture of lives.
Human:
17.Why do humans have so few genes?
In 2003,when the human genom project were being completing,when all biologists were ready to celebrate the great achievement,they amazedly found the number of genes were fewer than they originally estimated.Yes,human have about 25,000,but the estimated number is 100,000.By comparison,even an animal as simple as a wireworm has 20,000 genes.Arabidopsis thaliana has a few more than us,and rice doubles the number.Scientists presume the way genome works is more flexible and complicate than originally assumed.They are trying to find some molecular mechanism to do more work with fewer genes.
18.To what extent are genetic variation and personal health linked?
Long ago,scientists have found that some patients have different reactions to certain drugs.For example,a certain kind of muscle relaxant for anesthesia will make certain kind of people choke.Finally,scientists found it was because they had certain kind of genes.This brought a problem:will the research on genetic variation among different kinds of people advance the development of medical science and help develop better therapeutic means.That is to say,use medication according to individual DNA.Scienstists have identified some genes which interact with certain drugs.But it's too early to achieve actual individual drug use.
19.How much can human life span be extended?
Although still we can hardly see a centenarian,the average life of human have kept on increasing during the past several decades.For how will the trend continue?Though the research on experimental animals,sientists found they can prolong the animals' life span obviously by using some methods including restrict caloric intake.Can we apply these methods be applied to human?And for how long can they prolong human lifetime?Some scientists presume we can easily live to an age of 100 years old.However,long life will bring some troubles,like this one——social insurance.
20.What genetic changes made us uniquely human?
With the improvement of gene sequencing technology,scientists collected more and more complete genome sequences of varieties of spicies in their database,including human and many primates,such as chimp.We can easily recognize human and chimp,but at molecular level,this kind of differentiation is not so easy to obtain.The difference of DNA between chimps and us is merely 1.2%.It's a tiny number,but it means a difference of more than 30 million base pairs in absolute amount.Which of the 30 million differences on earth made us so unique after the separation of chimps and us?Scientists are trying to find the genetic differences which make us different from the other primates.And,of course,there are some other elements beyond genes,like culture,language,and technology.
21.How Are Memories Stored and Retrieved?
Good memories,bad memories,memories about equation solving,English words......they are undoubtedly storing in our brain.Where exactly they are?
In 1950s,the hippocampus area in the brain plays a very important role in the process of memory storing——if we resect it,the memory of the past will lost.But how do these nerve cells in hippocamus get information fixed.Scientists have found some molecules which participate the memory forming process.Besides,the forming of neuron synapse have relationships with memory forming,too.But the understanding of the operation mechanism of memory still couldn't satisfy the scientists——this mechanism is extremely important for us to understand ourselves.
22.Can we selectively shut off immune responses?
Organ transplantation is not rare in today's surgery,but there still exists the seemingly inevitable problem which doctor and patient needs to face——immunological rejection.The immune system of the patient will probably regard the transplanted organ as an "enemy",and attack it,and the surgery finally fail.To prevent this,doctor have to select the donor organ quite carefully,and for some of the patients,they need to take immunosuppresive drugs for a whole lifetime——obviously,it's not a good idea.Now scientists have found several possible methods to keep the immune system working without rejecting the transplanted organ.But we still need to wait for a long time for the clinical application.
23.Is an effective HIV vaccine feasible?
Every year the U.S. National Institutes of Health alone invests nearly $500 million on the search for a vaccine against HIV.Hitherto none of the vaccines is practically effective.Some skeptics contend that no vaccine will ever stop HIV,they argue that the virus changes too quickly during the process of replication.But the supporters found the vaccines can protect monkeys from Simian Immunodeficiency Virus(SIV),so they believe vaccines for HIV will come true.
24.What can replace cheap oil——and when?
Nobody denies that we will use up oil one day.Moreover,the oil production will probably go down quite soon.Despite these factors,we are impelled to find a substitute for oil by the threatening global warming.Solar power?Wind power?Nuclear power?Each of them has good potential,yet none of them is mature.
25.Will Malthus continue to be wrong?
In 1798,Malthus published his famous book "An Essay on the principle of population",argued that human populations will always tend to grow because it can't catch up with the growth of food supply,only disaster can stop the population growth.Now,200 years have past,we have 6 billion people on the planet,six times the number of Malthus's time,yet happily,the disaster he predicted never happens.To a great extent science prevents the disaster,but the the problem we still need to face——how can we make sure that no catastrophe happens in the future?