唧唧堂编辑二朵2013-12-29 4:41 AM

life before earth? 地球产生前的生命?

Abstract An extrapolation of the genetic complexity of organisms to earlier times suggests that life began before the Earth was formed. Life may have started from systems with single heritable elements that are functionally equivalent to a nucleotide. The genetic complexity, roughly measured by the number of non-redundant functional nucleotides, is expected to have grown exponentially due to several positive feedback factors: gene cooperation, duplication of genes with their subsequent specialization, and emergence of novel functional niches associated with existing genes. Linear regression of genetic complexity on a log scale extrapolated back to just one base pair suggests the time of the origin of life 9.7 billion years ago. This cosmic time scale for the evolution of life has important consequences: life took ca. 5 billion years to reach the complexity of bacteria; the environments in which life originated and evolved to the prokaryote stage may have been quite different from those envisaged on Earth; there was no intelligent life in our universe prior to the origin of Earth, thus Earth could not have been deliberately seeded with life by intelligent aliens; Earth was seeded by panspermia; experimental replication of the origin of life from scratch may have to emulate many cumulative rare events; and the Drake equation for guesstimating the number of civilizations in the universe is likely wrong, as intelligent life has just begun appearing in our universe. Evolution of advanced organisms has accelerated via development of additional information-processing systems: epigenetic memory, primitive mind, multicellular brain, language, books, computers, and Internet. As a result the doubling time of complexity has reached ca. 20 years. Finally, we discuss the issue of the predicted technological singularity and give a biosemiotics perspective on the increase of complexity. 论文摘要 对生物体遗传复杂性追溯至更古老时间的外推表明生命在地球形成之前就开始了。生命体可能最初产生自只有单个功能上等同单核苷酸的遗传元素的系统。我们预计通过非冗余功能性核苷酸数目大致测估的遗传复杂性将产生指数级增长。所呈现的这种成倍式增长归因于一些正反馈因素:比如基因合作,基因的复制及其随后的分化和与现存基因相关的新颖功能性生态位的出现。我们对遗传复杂性以对数为比例进行线性回归,外推至只剩单个碱基对,这表明生命起源于97亿年前。这个生命进化的宇宙时间尺度具有重要的后果:生命大约经过了长达50亿年的时间达到了等同于细菌的复杂性; 生命起源与进化到原核生物阶段的环境可能已经和设想中的地球环境有巨大差别; 我们的宇宙在地球起源之前还没有智慧生命产生,因此地球上的生命不可能是因智慧外星生物有意播种而来而是源自有生源说;从临摹而得的对生命起源的实验复制可能需要仿效许多累积罕见的事件;用于大概估计宇宙中文明数量的德雷克方程很可能是错误的,因为智慧生命才刚刚开始在我们宇宙中出现。先进生物体的进化速度因额外信息处理系统的发展而加快:比如表观遗传记忆,原始的思维,多细胞的大脑,语言,书籍,电脑和互联网。结果是复杂性加倍所需的时间已经大约达到20年。最后,我们讨论了预测的技术奇点的问题并且为复杂性的增长提供了生物符号学上的视角。

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