Hipotezy o powstaniu i wczesnej ewolucji życia

Abstrakt

The current status of the research concerning the origin and early evolution of life on Earth is discussed. In contrast to popular opinion, Charles Darwin never speculated about the origin of life on Earth and regarded such attempts as hopeless. However, nowadays the topic is studied intensively and during recent decades several important results have been obtained. New geological data reveal that Earth became habitable as early as 4.4 billions years before present; indeed, the first biogeochemical and paleontological findings indicate for some advanced biological activity already 3.8-3.5 billions years before now. Phylogenomic analyses allowed to envisage the last common universal ancestor (LUCA) of all extant organisms as a population of microorganisms engaged in horizontal gene transfer, not later than some 2 billions years ago. Two major theoretical scenarios of life origin and early evolution are being currently developed and their predictions experimentally tested: (1) "cool primeval soup" or "heterotrophic" theory, rooted in Oparin-Haldane hypothesis and in early experiments by S.L. Miller, proposing that life has developed in slightly reducing atmosphere and ocean, originally utilizing the deposits of organic matter which was produced in some abiotic processes; (2) "hot pizza" or "autotrophic" theory postulates that life originated at hydrothermal vents, from the very beginning exploiting autotrophically mineral substrates and redox potential. Neither of the theories suffices to explain how large macromolecules capable of self-replication and metabolism developed, although the next step of early life evolution, the "RNA world" seems to be better supported experimentally, including a successful synthesis, in "prebiotic" conditions, an active pirymidyne nucleotide, a functioning artificial protocell, and an autocatalytic rybosyme system capable of exponential growth and evolution. Yet, it is still poorly understood how the alleged RNA world could possibly evolve into the "DNA-protein world".