Forterre P
Institut de Génétique et Microbiologie, Université Paris-Sud, Orsay, France.
Planet Space Sci. 1995 Jan-Feb;43(1-2):167-77. doi: 10.1016/0032-0633(94)00167-p.
Molecular phylogenetic studies have revealed a tripartite division of the living world into two procaryotic groups, Bacteria and Archaea, and one eucaryotic group, Eucarya. Which group is the most "primitive"? Which groups are sister? The answer to these questions would help to delineate the characters of the last common ancestor to all living beings, as a first step to reconstruct the earliest periods of biological evolution on Earth. The current "Procaryotic dogma" claims that procaryotes are primitive. Since the ancestor of Archaea was most probably a hyperthermophile, and since bacteria too might have originated from hyperthermophiles, the procaryotic dogma has been recently connected to the hot origin of life hypothesis. However, the notion that present-day hyperthermophiles are primitive has been challenged by recent findings, in these unique microorganisms, of very elaborate adaptative devices for life at high temperature. Accordingly, I discuss here alternative hypotheses that challenge the procaryotic dogma, such as the idea of a universal ancestor with molecular features in between those of eucaryotes and procaryotes, or the origin of procaryotes via thermophilic adaptation. Clearly, major evolutionary questions about early cellular evolution on Earth remain to be settled before we can speculate with confidence about which kinds of life might have appeared on other planets.
分子系统发育研究揭示了生物界的三分法，即分为两个原核生物类群——细菌和古菌，以及一个真核生物类群——真核生物。哪个类群是最“原始的”？哪些类群是姐妹群？这些问题的答案将有助于勾勒所有生物的最后共同祖先的特征，这是重建地球生物进化早期阶段的第一步。当前的“原核生物教条”声称原核生物是原始的。由于古菌的祖先很可能是嗜热菌，而且细菌也可能起源于嗜热菌，原核生物教条最近与生命起源于高温的假说联系在一起。然而，最近在这些独特的微生物中发现了非常精巧的高温生存适应机制，这对当今嗜热菌是原始的这一观点提出了挑战。因此，我在这里讨论一些挑战原核生物教条的替代假说，比如存在一个具有介于真核生物和原核生物之间分子特征的共同祖先的观点，或者原核生物通过嗜热适应起源的观点。显然，在我们能够自信地推测其他行星上可能出现哪种生命之前，关于地球早期细胞进化的主要进化问题仍有待解决。
