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> The natural time period of evolution is the generation; meaningful change must occur over that sort of period Unless you have specific education in this area

> The natural time period of evolution is the generation; meaningful change must occur over that sort of period Unless you have specific education in this area, this is contrary to the classes I took in university on the topic of animal biology. There is no "natural time period" for evolution, as you say. Meaningful change usually does not happen over any arbitrary period. It is typically a random event that spikes rarely in a species, and usually there are long periods of zero change until such spikes occur between these changes. I suspect you are postulating on what evolution is without actually knowing how it most often emerges.

mannykannot 9y ago
Firstly, a matter of terminology: my use of 'natural period' may be wrong here, if it implies a cyclical process; I am not sure what might be the correct term, so I shall use 'characteristic period'. You are confusing two different but related issues, and may have misunderstood your professor. The timing of large effects (speciation, for example) is unpredictable, and there are long periods in the history of any given line of descent during which no speciation-level evolution occurred (note that the article is about evolution at a much smaller scale than speciation. These events are unpredictable in detail, but occur much more frequently.) As for the process by which it happens - variation and natural selection - the generation is, to a first approximation, a characteristic unit of time. A mutation occurs at a point in time, but it is only subject to being selected by natural selection if and when it is passed in the next generation, and natural selection works by creating more of the next generation on account of it. This is somewhat complicated by the appearance of neutral mutations, which do not have effects that are selected for or against. These take the genome on a continual but evolutionarily directionless random walk, for which the characteristic time period is the generation. There is the possibility that, as a consequence of these random walks, any given allele's frequency in the population will drop to zero, after which it will not reappear unless it is recreated by another mutation. While neutral mutations, by definition, have no evolutionary effect at their inception, they may become significant either as a consequence of a change in the environment or through the allele's interaction with, or modification by, a subsequent mutation. Whenever that happens, however, natural selection still works by changing the occurrence of the allele from one generation to the next. On reflection, my phrase "meaningful change must occur over that sort of period, or it is not going to happen at all" is inaccurate; to express what I was thinking, I would now write that "when evolution occurs, it is manifest from one generation to the next." I see that you are aware that evolution has a tendency to occur in spikes, so it seems odd that you would write, in your initial post, "Considering the extraordinary amount of time it takes for evolution to do anything at all..." There is no requirement for there to be long periods of stasis between events.

mannykannot 9y ago

Firstly, a matter of terminology: my use of 'natural period' may be wrong here, if it implies a cyclical process; I am not sure what might be the correct term, so I shall use 'characteristic period'. You are confusing two different but related issues, and may have misunderstood your professor. The timing of large effects (speciation, for example) is unpredictable, and there are long periods in the history of any given line of descent during which no speciation-level evolution occurred (note that the article is about evolution at a much smaller scale than speciation. These events are unpredictable in detail, but occur much more frequently.) As for the process by which it happens - variation and natural selection - the generation is, to a first approximation, a characteristic unit of time. A mutation occurs at a point in time, but it is only subject to being selected by natural selection if and when it is passed in the next generation, and natural selection works by creating more of the next generation on account of it. This is somewhat complicated by the appearance of neutral mutations, which do not have effects that are selected for or against. These take the genome on a continual but evolutionarily directionless random walk, for which the characteristic time period is the generation. There is the possibility that, as a consequence of these random walks, any given allele's frequency in the population will drop to zero, after which it will not reappear unless it is recreated by another mutation. While neutral mutations, by definition, have no evolutionary effect at their inception, they may become significant either as a consequence of a change in the environment or through the allele's interaction with, or modification by, a subsequent mutation. Whenever that happens, however, natural selection still works by changing the occurrence of the allele from one generation to the next. On reflection, my phrase "meaningful change must occur over that sort of period, or it is not going to happen at all" is inaccurate; to express what I was thinking, I would now write that "when evolution occurs, it is manifest from one generation to the next." I see that you are aware that evolution has a tendency to occur in spikes, so it seems odd that you would write, in your initial post, "Considering the extraordinary amount of time it takes for evolution to do anything at all..." There is no requirement for there to be long periods of stasis between events.