Small Steps---how small can they be?

Hi InGodITrust, So using some "large leaps" means micro steps are not possible?The smallest "leap" would be neutral mutations - ones that offer neither benefit nor hindrance to breeding or survival in the current selection environment. You could call that a "null" step. Yet several of your examples could co-evolve with continued adaptation by mutation and selection over many generations - other snakes don't stop evolving while waiting for a fang to be developed, so the poison snake is not dependent on it to evolve. And individual mutations have a discrete number of changes rather than a blended transformation. This leads to the conclusion that any apparently blended transformation, such as the poison viper fang, would be the result of several mutations. Think of evolution as being opportunistic rather than deterministic: organisms take advantage of the opportunities provided by their inherited variations to gain an advantage over other organisms for breeding or survival in the ecology they inhabit - which may be a new ecology, due to those variations, that they now have the opportunity to inhabit and adapt to.Also, while we can identify several steps that may have occurred in the development of a single feature, that does not mean that the development is a linear progression. Evolution does not move from point A to point B - it's more like the flight of a butterfly landing on a flower at random in a field. How much speed does a butterfly need to cross a field? The known rates of mutation are vastly higher than the rate needed to develop any feature known in the time frame we know was available.Enjoy.Edited by RAZD, : No reason given.

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Rebel American Zen Deist
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Hi Dr Adequate, we should be careful not to oversimplify and understate the issue. First off, the rate of mutation may be relatively steady in mature populations, but they have been shown to increase when the individuals are under stress. This is due to the relationship between development and ecology. Hormones affect development and stress affects hormones, where the stress comes from the ecology (hot, dry, predator dominated, etc).Second, the ability of a population to fix mutations (ie pass them on to following generations) is related to the level of selection pressure: when selection pressure is low, more marginal mutations pass muster (survive long enough to breed), and resulting in more variety of mutations within the population, while under high selection pressure these individuals fail to meet the mark and the number of mutations available to the next generation is reduced. This has been done, and the results show that the rate of mutations can vary in specific populations. When we try to apply that knowledge to the historical perspective, what we are really measuring is the rate of fixed mutations.The number of fixed mutations is necessarily smaller than the number of mutations, and the proportion is variable (as noted above), so they cannot be used to extrapolate a rate of mutation for the population in general. Curiously, we get a kind of cart and horse situation here. We take, for example, the genomes of human and chimpanzee and bonobo and gorilla, and from this family tree we can see that the rates of fixed mutations in these different populations occurred at different rates, and this is generally reported as an average rate of mutation for each population - there is no way to find max and min rates within those periods.We can compare those to the known rates of mutations today and see that they are within the range of fixed mutations in populations from the known highs to the known lows.Many times we also find that even the low rates of known mutations are much more than sufficient for evolution to have occurred in some populations -- in other words that evolution can be lazy in getting from one place to another -- but have yet to find an instance where the amount of fixed mutations cannot be explained by known rates of mutation and the fixing of mutations in a population. I agree that his aspect of the field of genetics is still in the infancy stage, an exciting place where discoveries are waiting to be made. But I predict it will take much less than 20 years ...Enjoy.

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we are limited in our ability to understand
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Rebel American Zen Deist
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Hi Wounded King, correct me if I'm wrong, but it seems to me that there are a number of processes going on, which make it difficult to determine an accurate mutation rate outside the lab. Yes, that is part of it - organisms produce different hormones at different levels while under stress, and this affects both the ability to reproduce and the resulting development.Salamanders when exposed to dry conditions can divert from normal growth to early ability to reproduce, and when this happens their normal development is arrested, such that the larval stage gills are not lost. When normal conditions return the salamanders revert to development along the normal lines, with the gills being lost.The mudpuppy salamander has evolved to reach reproductive ability while retaining the gills and some other juvenile traits (see pedomorphosis). This developmental interruption likely has become fixed in the population through subsequent mutations and selection -- because the opportunity occurred for this to happen as a result of the environmental stress response.A similar thing occurs during speciation, where an existing population has an opportunity to branch out into a secondary environment, which then allows more new mutations to be fixed in the parent population before it divides into the daughter populations that specialize in the different environments.This relates more to the rate of mutation fixing than to mutations per se, however, when we compare genomes of populations we are also comparing fixed mutation rates. Mutations that don't make it past the first generation are not measured. My understanding here, is that the (normal? evolved?) repair (control) mechanism/s break down, allowing more dodgy division to occur. I thought I saw a reference to similar in a multicellular life form, but can't find it at the moment.

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we are limited in our ability to understand
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Rebel American Zen Deist
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