宇宙中新的生命形式存在何方?
文章来源:未知 文章作者:enread 发布时间:2012-05-09 05:53 字体: [ ]  进入论坛
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The idea of discovering a new form of life has not only excited astronomers1 and astrobiologists for decades, but also the wider public. The notion that we are the only example of a successful life form in the galaxy2 has, for many, seemed like an unlikely statistic3, as we discover more and more habitable planetary bodies and hear yet more evidence of life's ability to survive in extreme conditions. A new essay, published May 8 in the online, open-access journal PLoS Biology, examines what really constitutes 'life' and the probability of discovering new life forms.

Professor Gerald Joyce, from The Scripps Research Institute in La Jolla, California, discusses in the essay the basic requirements for a life form to exist. He says, "Life self-reproduces, transmits heritable information to its progeny4(子孙,后裔) , and undergoes Darwinian evolution based on natural selection." He refers to this heritable information as 'bits' (for life as we know it, this includes the four bases of DNA), and explains that although Darwinian evolution results in new combinations of these bits, this does not define a new or alien form of life. Indeed, to date no truly new life form has been discovered -- either in extreme environments on Earth or on other planets -- that contains new bits, despite evidence suggesting life on meteorites5(陨石) recovered in Antarctica, or on any of the so-called 'habitable' planets discovered in our galaxy.

How could a truly new life form arise? Joyce explains that an organism could either arise directly through chemistry, or spin off from existing biology. For the former, a life form would self-organize "into a bit-generating system." It's thought that this is how life originated on Earth; from a primordial6(原始的) soup of chemicals in an aqueous(水的) environment that generated self-replicating molecules7, which then mutated and evolved. Joyce argues, "A life form that arises directly from bit-free chemistry would be considered 'new' from the outset, while one that derives8 from a biological cell would have a long way to go before reaching the threshold."

It is in these differences between chemical or biological initiation9 -- that is to say, whether the life form has developed from an existing life or seemingly independently -- that confusion and misinformation occurs surrounding the probability of a new life being discovered or created. Given that we only know of one life form -- our own -- we can't meaningfully estimate the probability of new life arising, either on Earth or elsewhere.

"I think humans are lonely and long for another form of life in the universe," says Joyce, "preferably one that is intelligent and benevolent10(仁慈的) . But wishing upon a star does not make it so. We must either discover alternative life or construct it in the laboratory. Someday it may be discovered by a Columbus who travels to a distant world or, more likely in my opinion, invented by a Geppetto who toils11 at the workbench."

In the accompanying PLoS Biology Podcast, Joyce discusses in more depth the ability of scientists to discover the origin of novel life forms, and whether the emerging field of synthetic12 biology can actually lead to new forms of life.



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1 astronomers 569155f16962e086bd7de77deceefcbd     
n.天文学者,天文学家( astronomer的名词复数 )
参考例句:
  • Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
  • Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪,为什么只有土星有光环。 来自《简明英汉词典》
2 galaxy OhoxB     
n.星系;银河系;一群(杰出或著名的人物)
参考例句:
  • The earth is one of the planets in the Galaxy.地球是银河系中的星球之一。
  • The company has a galaxy of talent.该公司拥有一批优秀的人才。
3 statistic QuGwb     
n.统计量;adj.统计的,统计学的
参考例句:
  • Official statistics show real wages declining by 24%.官方统计数字表明实际工资下降了24%。
  • There are no reliable statistics for the number of deaths in the battle.关于阵亡人数没有可靠的统计数字。
4 progeny ZB5yF     
n.后代,子孙;结果
参考例句:
  • His numerous progeny are scattered all over the country.他为数众多的后代散布在全国各地。
  • He was surrounded by his numerous progeny.众多的子孙簇拥着他。
5 meteorites 12efd1ed528a28fe1f7cb667a7fbc1e0     
n.陨星( meteorite的名词复数 )
参考例句:
  • Small meteorites have left impact craters all over the planet's surface. 这个行星的表面布满了小块陨石留下的撞击坑。 来自《简明英汉词典》
  • One theory about the existence of extraterrestrial life rests on the presence of carbon compounds in meteorites. 地球外存在生命的理论是基于陨星上存在碳化合物质这一事实的。 来自《简明英汉词典》
6 primordial 11PzK     
adj.原始的;最初的
参考例句:
  • It is the primordial force that propels us forward.它是推动我们前进的原始动力。
  • The Neanderthal Man is one of our primordial ancestors.的尼安德特人是我们的原始祖先之一.
7 molecules 187c25e49d45ad10b2f266c1fa7a8d49     
分子( molecule的名词复数 )
参考例句:
  • The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
  • Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里,大分子裂变为小分子。
8 derives c6c3177a6f731a3d743ccd3c53f3f460     
v.得到( derive的第三人称单数 );(从…中)得到获得;源于;(从…中)提取
参考例句:
  • English derives in the main from the common Germanic stock. 英语主要源于日耳曼语系。 来自《简明英汉词典》
  • He derives his income from freelance work. 他以自由职业获取收入。 来自《简明英汉词典》
9 initiation oqSzAI     
n.开始
参考例句:
  • her initiation into the world of marketing 她的初次涉足营销界
  • It was my initiation into the world of high fashion. 这是我初次涉足高级时装界。
10 benevolent Wtfzx     
adj.仁慈的,乐善好施的
参考例句:
  • His benevolent nature prevented him from refusing any beggar who accosted him.他乐善好施的本性使他不会拒绝走上前向他行乞的任何一个乞丐。
  • He was a benevolent old man and he wouldn't hurt a fly.他是一个仁慈的老人,连只苍蝇都不愿伤害。
11 toils b316b6135d914eee9a4423309c5057e6     
参考例句:
  • It did not declare him to be still in Mrs. Dorset's toils. 这并不表明他仍陷于多赛特夫人的情网。
  • The thief was caught in the toils of law. 这个贼陷入了法网。
12 synthetic zHtzY     
adj.合成的,人工的;综合的;n.人工制品
参考例句:
  • We felt the salesman's synthetic friendliness.我们感觉到那位销售员的虚情假意。
  • It's a synthetic diamond.这是人造钻石。
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