Chela-Flores, Julian. “The Phenomenon of the Eukaryotic Cell.”

The focus of Julian Chela-Flores’ paper is the possibility of the evolution of life elsewhere in our solar system. He first reviews Big Bang cosmology, including its modifications by Guth and Linde. Next he turns to the origin of life on Earth from the 1920s to the present. Although scientists view organic matter as inexorably self-organized according to the laws of physics and chemistry, the complete pathway from the inanimate to life on Earth has not been reproduced experimentally, nor has the importation of organic molecules from space been ruled out. Meanwhile research is now underway in exobiology and bioastronomy via the ongoing space missions. Issues include cross-contamination of either Earth, Mars, or Europa, comparative planetology, the search for extraterrestrial homochirality (SETH), the search for extraterrestrial eukaryotes (SETE), and, since the 1960s, the search for extraterrestrial intelligence (SETI). He concludes this section with speculations on the future of evolution on earth.

Next, Chela-Flores describes recent topics including chemical evolution in the universe, the pathways from precursors to biomolecules, modern taxonomy, the terminology for single- celled organisms, and the evolution of prokaryotic cells in the Precambrian period. He then discusses the evolution of eukaryotes, including the role of oxygen and iron in their first appearance, and the identification of eukaryotes that are morphologically similar to prokaryotes. Next Chela-Flores takes us from eukaryogenesis to the appearance of intelligent life on Earth. Here he presses his case for the inevitable increase of complexity in the transition from bacteria to eukarya. Physics and chemistry imply an “imperative” appearance of life during cosmic evolution which he formulates as a bold, but in principle testable, hypothesis: “once the living process has started, then the cellular plans, or blueprints, are also of universal validity.” In short, prokaryotes lead to eukaryotes, and they do so universally. Provided that planets have the appropriate volatiles (particularly water and oxygen), Chela-Flores argues that not only life, but eukaryogenesis, is bound to occur. Within the next two decades, a new generation of space missions could test his hypothesis. Moreover, the hypothesis bears on the question whether these missions should search for Earth-like life or something entirely different. Chela-Flores gives various responses to this question, including the relevance of SETE to SETI and the significance of the discoveries of the Murchison and Allan Hills meteorites that originated on Mars.

In closing, Chela-Flores maintains that there is a second environment in our solar system, the Jovian satellite Europa, in which the eukaryogenesis hypothesis may be tested. He first describes other possible sites for extremophiles and other microorganisms, including the atmospheres of Europa, Io, Titan, and Triton, and possible hot springs at the bottom of Europa’s (putative) ocean. Then he identifies parameters that may characterize the degree of evolution of Europan biota both at the ice surface and its ocean. He concludes again that a space mission could test these ideas in the near future.

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