Your grandfather and grandmother knew little of the world outside of their village or town， or even of China as the big country that it is. Today you， their grandchildren， know a lot about the world outside of China. Indeed， at any time， we can see people living， loving， unfortunately sometimes fighting in wars， in any part of the Earth， at the very moment that it is happening， just by turning on our television set. On that same television set， sometimes we can see pictures of the distant planets， of the even more distant galaxies1， or of the inside of our bodies， such as the beating heart of a live person or even of a living fetus2 still in the belly of his mother.
We have sent repeatedly men to walk on the moon to explore it. We understand the forces that bind the components3 of atoms and we know how to utilize " atomic energy" to create unlimited amounts of power either to make electricity or to create immensely destructive weapons.
We understand the biological chemistry which leads a seed of a plum tree， of a bamboo， of a pine to reproduce another plum tree， bamboo， or pine. We also know， how incredible， that that biochemistry is identical4 to that which controls the making of beetles or dragonflies5， or tuna6 fish or cranes7， horses， or humans. The genetic code which we have known how to read for about thirty years allows us also to modify the biochemistry of the genes so that we can induce microbes8 or yeast9 to make unlimited quantities of human growth hormone10 or human insulin11 for instance， or even to correct the problem of genetically transmitted diseases.
We know how to build supersonic12 airplanes like the Concord in which people travel faster than the speed of sound. We know how to go see and explore the bottom of the deepest oceans， to make calculating machines so fast that in one hour some of these computers can solve mathematical problems that would take 300 years for 10 mathematicians working 12 hours a day to get the solution.
We know how to prevent many diseases by vaccination13， we know how to grow enough food to feed the whole population of the earth. We know how our brain is built but we are just beginning to understand how it works.
What you have been reading here， reflects the current achievements of science and the applications of science. Science is the search for new fundamental knowledge to understand the world around us， with no specific interest as to whether that knowledge will be useful， just like the writing of music or creating a painting. The remarkable thing is that all fundamental knowledge leads to practical applications like any of those I mentioned above. Our ancestors explained the world by mythology， sometimes claimed to have been given to them by gods. Today we explain the world by science， and all science is created by the human brain， not given to us by any god. The more we know in science， the more we realize that there is much more to know.
To be young nowadays and able to go to school and to a university is one of the most important opportunities in the life of a young person. To learn from the people who have made the discoveries which represent the current knowledge of the human race is a chance that should not be passed. Being a scientist is an exhilarating14 life but also a difficult one， because discoveries are usually not easy. It took me with my collaborators more than 10 years of work and handling of many tons of brain tissue from farm animals eventually to isolate15 1mg of the first of the " brain hormones" ， new molecules16 which are in the brain of all of us and which control the growth of our body， the appearing of puberty17 in all of us boys or girls， later control our sex life and our reproduction18 life. That was a lot of difficult work， sometimes frustrating and discouraging. But if one is honest with himself， one always learns from mistakes， can correct a concept or a hypothesis19 and work further， eventually to reach the goal. To be a scientist requires the most impeccable20 intellectual honesty.
There are still many， many things to be discovered， and understood in the way the brain works——how do we speak， how do we see， how are we conscious of ourselves， why are we sleeping and have to sleep to remain healthy， in the way the universe was formed， in inventing new ways in the thinking of people to preserve the ecology of the planet which is now damaged by the misuse of all that wonderful knowledge. We still have to cure all cancers， to find a vaccine21 for AIDS so that the AIDS epidemics disappear. We will want to share all our knowledge with all the people in the world so that we all have clean water to drink and enough to eat， we all have security in our lives so as not to be envious of our neighbors thus living in peace with the rest of the world. To be young nowadays is to live at one of the most extraordinary times in the history of man because we know so much， know how to learn more， and know that each of us can actually move and modify the world around us and bring comfort， happiness， dignity and peace to all of mankind.
你们的祖父母们对于他们所居住的村庄或城镇以外的世界了解得很少，即使对中国这样一个大国也很少了解。而今天，你们作为他们的后代，却对中国以外的世界知道得很多。在任何时候，只要我们打开电视机，就能看到世界的任何一个角落，看到那一刻那里正在发生什么事，看到各地人们的生活，人们的爱，遗憾的是有时也会看到战争。同样是通过电视机，我们有时能看到遥远星球的图像，甚至看到更远的星系；我们有时还能看到人类自己身体内部的情况，例如跳动的心脏，甚至母亲腹内的胎儿。
人类已经屡次登上月球去探索它的奥秘。我们已经了解了原子之间结合的力量，知道如何利用原子能去创造无限巨大的能量——或是把它用于发电，或是制造巨大的毁灭性武器。
我们已经了解生物化学，可以利用李子树、竹子、松树的一粒种子再复制出另外一棵李子树、竹子和松树。我们也知道，利用这种生物技术可以复制出甲虫、蜻蜓、金枪鱼、仙鹤、马或人类自己，这一切简直不可思议。大约30年以来，人类破译了遗传密码，这使我们可以修改基因的生物化学从而可以通过诱导微生物（细菌）或酵母来制造出无数促进人体发育的激素或胰岛素，甚至能够治疗遗传基因带来的某些疾病。
我们知道如何建造"协和式"那样的超音速飞机，人们可以以比声音还快的速度在空中旅行。我们知道如何下潜到最深的海底去探索；我们已经可以制造出计算机，有的计算机运算速度之快可以用1个小时就解决原来需要10个数学家、每天工作12个小时、花费300年才能解决的数学问题。
我们知道如何通过免疫接种来预防许多疾病；我们知道如何生产出足够的食物养活地球上所有的人；我们知道人类的大脑智力是如何形成的，但我们还只是刚刚开始了解它是如何运作的。
你在这里所读到的一切，反映了目前科学和科学应用的成就。科学是探索新的基础知识，以解释我们周围的世界。至于这一知识将来是否有用，它并不特别关注，就像创作音乐和绘画一样。但是值得注意的是，就像任何一件我上面提到的事物一样，所有这些基础知识都会带来实际应用的效果。我们的祖先用神话来解释世界，有时声称是神灵赐予他们的。而今天，我们用科学来解释世界，所有的科学又是通过人的大脑创造出来的，并不是哪一个神灵给予我们的。我们对科学知道得越多，就越会意识到，还有许多许多东西有待我们去了解。
现在的青年人能够上学、上大学，这是一生中最重要的机会之一。向那些科学上有所发现者们学习也是一个机会，这个机会不应该错过，因为他们的发现代表了人类现今最新的知识。当一个科学家，是令人振奋的，但同时也是非常艰难的，因为要有所发现通常是很不容易的。我和我的合作者们花费了10多年的时间，研究和处理了许多吨家畜的脑组织，最后才分离出1毫克的"脑激素".这是一种新的分子，它存在于我们所有人的大脑之中，它控制着我们身体的生长，所有男孩和女孩青春期的出现，以后又控制我们的性生活和繁衍。那是一项非常艰巨的工作，有时会感到灰心和泄气。但如果一个人以诚实的态度看待自己，他总会从错误中学到一些东西，并能改正错误的观念或假设，从而使研究更为深入，最终达到目标。要成为一个科学家，需要最无懈可击的理性的诚实。
在大脑的活动方式领域，仍然有很多很多知识等待着人们去发现和理解——我们是如何说话的？我们是怎样看东西的？我们是如何意识到我们自身的存在的？为什么我们要睡觉？为什么我们为保持健康而不得不睡觉？此外，在其他方面也还有许多问题有待人们发现——宇宙是如何形成的？如何使人们产生新的思维方法来保护地球上的生态环境？我们目前的生态环境由于滥用和错用各种新奇的知识而遭到破坏。我们还得设法治愈各种癌症，发现艾滋病的疫苗，使艾滋病不再危害人类。我们愿意与世界上所有的人一起分享我们的全部知识，让我们大家都能喝上清洁的水和有足够的食物。我们都需要有安全感，不要嫉妒邻里，与世界上的所有人和平相处。当今青年一代正生活在人类一个最不寻常的历史时期。因为我们懂得很多，知道如何去学习更多的知识，知道我们每一个人确实能够去改变我们周围的世界，给全人类带来舒适、幸福、尊严与和平。
注释：
1.galaxy n.（galaxies）[天]星系
2.fetus n.胎，胎儿
3.component n.（组）成（部）分
4.identical adj.（完全）相同的，一模一样的
5.dragonfly n.蜻蜓
6.tuna n.[鱼]金枪鱼
7.cranes n.[鸟]鹤，鹭，鹳
8.microbe n.微生物
9.yeast n.酵母
10.hormone n.[生化]激素，荷尔蒙
11.insulin n.[生化]胰岛素
12.supersonic adj.超音速的
13.vaccination n.种痘，接种
14.exhilarating adj.使人兴奋的
15.isolate vt.使分离
16.molecule n.[化]分子
17.puberty n.青春期，发育期
18.reproduction n.生殖，繁育
19.hypothesis n.假设，前提
20.impeccable adj.无可挑剔的
21.vaccine n.疫苗，菌苗