Biological Evolution — Formation of Protobionts

Biological evolution begins with the transition from simple organic chemistry to structures that behave like living matter. Abiotically produced molecules can spontaneously self-assemble into droplets that enclose a watery interior chemically distinct from their surroundings — scientists call these spheres protobionts. Liposomes are one such example: lipids in solution that self-assemble into a lipid bilayer membrane; once some of the enclosed proteins acquired enzyme-like activity, the molecules inside could multiply faster. Coacervates containing nucleoprotein and nutrients, bounded by a limiting membrane, began to resemble a virus or a free-living gene; as more genes came together, they formed 'proto-viruses' broadly comparable to present-day viruses. Two early cell types are thought to have emerged from this process: one, containing loose clumps of nucleoprotein within the cell substance, resembled the Monera and is considered ancestral to modern bacteria and blue-green algae; the other, whose nucleoprotein clumps condensed into a membrane-bound central mass, is called Protista-like. As food sources in the primitive ocean dwindled, the descendants of these early Monera- and Protista-like cells had to diversify their nutrition — evolving parasitism, saprophytism, predation, and chemosynthesis or photosynthesis. As photosynthetic organisms increased, free oxygen accumulate …