中文摘要：

关于生命的起源和演化对于公众和学术界都是一个深刻的问题.最初的生命可能起源于原始的地球环境,也可能来自星际间的尘埃、彗星和陨石等.生命的本质是一个化学过程,其最基本的特征是能够自我复制和新陈代谢.在前生命时期地球特定的物理化学条件下,由有机小分子的相互作用聚合形成了主宰生命的核酸、蛋白质及其他大分子物质,之后逐渐演化形成具有新陈代谢、自我复制能力的原始生命体,最终产生生命的基本单元细胞.1859年,英国博物学家查尔斯·达尔文在《物种起源》一书中提出了进化论的观点,并且认为所有现存的和已灭绝的生物都有一个共同的起源,后人将之称为所有现存物种的共同祖先（last universal common ancestor,LUCA）.生命的起源和演化是一个极其复杂的问题,本文主要从这3个方面入手：（1）LUCA的遗传物质是DNA还是RNA？（2）LUCA是简单的还是复杂的？（3）LUCA的代谢特征有哪些？希望能让读者对LUCA和关于LUCA的讨论有一个大体的认识.

英文摘要：

Life, in essence, is defined as a chemical process characterized by the ability to self-replicate and metabolize. Abiogenesis（i.e., the origin of life） has been the subject of extensive controversies for centuries. Many scientists subscribe to Charles Darwin＇s notion that all organic beings that have ever lived on Earth may be descended from a primordial life form commonly referred to as the last universal common ancestor（LUCA）. The age of the Earth is about 4.5 billion years and the earliest life may exist more than 3.5 billion years ago according to fossil evidence. The precursor molecules necessary for life may have come from meteoroids, comets, interstellar dust, or from Earth itself. It has been posited that life on Earth, or LUCA, was an evolutionary outcome of the RNA world, a period of time when the primary living substances comprised of RNA — or something chemically similar. Several observations suggest that RNA could have served genetic, catalytic and regulatory roles before the evolution of DNA and proteins. However, the question that still remains to be answered is whether LUCA＇s genetic information was carried within the RNA molecule, or had it already evolved to a higher stage of DNA genome. Carl Woese proposed that LUCA began as an ambiguous progenote, a community of organisms that lived in a pool where they could share genes with each other. He further theorized that it then separated to three lines of descent including bacteria, archaea and eukaryote. Phylogenetic analysis based upon whole genomes revealed that LUCA was common ancestor of bacteria and archaea, with eukaryote diverged from some lineages of Archaea. Recent work using phylogenetic and metabolic reconstruction analysis suggested that LUCA might have been anaerobic, thermophilic, CO2-fixing, H2-dependent with Wood-Ljungdahl pathway, and N2-fixing. Although many efforts have been made by scientists to understand LUCA, it still remains an enigma. Here, in this comment, we will briefly summarize different perspectives conce