Rates, patterns, and effectiveness of evolution in multi-level situations.

Abstract

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...

Punctuated equilibria: the tempo and mode of evolution reconsidered

“…3. Darlington (1976) would separate mac roevolution into small-population events for the rapid production of many species and large-population events for the development of broad and general adaptations. Adaptive radiations begin with the evolution of key adaptations in large populations, followed by their general deployment through speciation in small ones.…”

Anatomical Variation, Hominins, Species, and Self-Domestication

“…Attempts have been made recently to apply the same principle on early hominid evolution [77] by combining it with a "neural crest hypothesis." These attempts are confused by the myriad selective agents and ideas of directed evolution, though one might conceive of a paradigm as proposed by Darlington [78] of a "period of self-acceleration." During this period, an explosive organic evolutionary process for bipedalism followed by a hiatus and then a secondary "pulse" driven by population increase occurred.…”

The cost of evolution and the imprecision of adaptation.

“…Serial cases Case F. Now consider a more complex case, of serial substitution, which modifies (but does not invalidate) some of the preceding generalizations. Suppose that, in a given population, 1000 offspring are conceived; that 100 of them are homozygous for recessive alleles that kill them before or during birth, their loss going to the costs of eliminations of the lethal alleles; that of the remaining 900, 500 die nonselective deaths, by accidents including random predation; that of the remaining 400, 390 are selectively eliminated before maturity, their loss going to the costs of substitutions of alleles that affect immatures; and suppose finally that, of the 10 This case suggests two additional generalizations. [15] Substitutions made in series need not interfere with each other, and there is no obvious limit to the number of serial substitutions that may go on concurrently in an organism with a complex ontogeny.…”

“…[6] A consequence of ¶ 5 is that multi-level (feedback) selection should favor genetic systems in which genes (alleles) are linked or combined into sets which are selected as wholes. "Regulator genes" (4) 10). (These limits are modified in serial substitutions, e.g., Case F.) [9] A consequence of 8 is that genetically solvent populations, that are well adapted to their environments and carry relatively small unpaid substitutional debts, can make and pay for new adaptations better than can populations still heavily in debt.…”