Evolution is a multi-level process. Both actual evidence and theoretical considerations suggest as a first generalization that evolution both at single levels and in series of increasingly complex levels decelerates with time. Additional evidence, the expected difference between rapid nonadaptive speciation in small populations and effective adaptation in large ones, and analysis of explosive evolution suggest further that effective adaptive evolution occurs primarily in large populations, and that segments of such evolution tend to begin slowly; accelerate, sometimes explosively, and then decelerate. The segments are irregular, and do not occur at regular intervals. However, the explosive evolution of a generaI adaptation pre-adapts to and is often followed by an explosive radiation of derivative lineages. This description seems to fit the origin and initial radiation of mammaIs, and the evolutionary history of man and man's cultures. Evolutionists recognize that evolution is a multi-level process but rarely apply the multi-level concept consistently. Here, I shall try to apply it to an analysis of rates, patterns, and effectiveness of evolution, which is a subject of current interest. For a statement of some of the concepts of multi-level evolution see ref. 4), indicates that both bacteria and blue-green algae existed at least 3.1 billion years ago and may already have been using chlorophyll, and this suggests that the main groups of prokaryotes evolved and separated rapidly, very early in their history, and that evolution of their primary adaptations then slowed down rather than speeded up.Supposed fossil eukaryote cells in the Bitter Springs formation in the Late Precambrian of Australia are now thought to be partially degraded prokaryote blue-green algae, and all other older supposed eukaryote fossils are doubtful too, according to a very recent paper by Knoll and Barghoorn (5). These authors think that the eukaryote (nucleated) cell may not have originated until just before the Cambrian, less than 1 billion years ago, and that multicellular eukaryotes may then have evolved "quite rapidly"; all the major eukaryote phyla, except the chordates, appear fossil in the Cambrian. This suggests a period of rapid evolution and primary adaptive radiation of eukaryotes, followed by a slowing down of the primary lines of adaptation. (But the unknown earlier stages of evolution of the exceedingly complex eukaryote cell may have been more gradual.) So, it is an hypothesis consistent with the apparent facts that prokaryote and eukaryote origins followed a common pattern, of a period of rapid evolution and diversification, followed by a slowing down of the primary adaptive processes, although in both cases secondary adaptive radiations occurred from time to time in separate phyletic lines.Fossil Evidence of Rates of Evolution. Simpson (6) describes actual rates of evolution indicated by the fossil record. He concludes that the rates have varied enormously in different comparable groups at the same time, and in the...
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