Mutation

I'm copying the question 'cause otherwise it might be buried. I'm not DNAUnion, who's the only self-proclaimed uber-expert on the forum, however I might be able to answer this. Mutations cause (usually minor) changes in phenotype all the time - it's one of the primary means by which variation arises in a population. No sexually-reproducing population is genetically homogenous. Most mutations, regardless of phenotypical effect, are considered neutral because they have no effect on the organism's fitness (which is based on the overall phenotype/environment interaction). IOW, the determination of "neutral" isn't that the mutation has no effect on the phenotype, rather that it is "neutral" in regards to fitness. Anything that increases the organism's marginal fitness is considered beneficial, anything that decreases the organism's marginal fitness is detrimental. Obviously, anything else is neutral.Where's Mammuthus when we need him? I'm sure he's got 50 or more papers at his fingertips which discuss the issue in great and glorious detail.

Hi Milagros.It wasn't my intention to get involved in this thread, as I figured you had enough people arguing with you. However, as I read through it, I was continually bothered by something that I couldn't quite put my finger on. It wasn't until your succinct restatement of the points you were arguing in this post that I was able to see what the problem was. We have a significant and fundamental conceptual error that has slipped through. Although I suspect you initiated it, your opponents have perpetuated it, at least by letting it slide. Let me see if I can clarify: Nowhere in any literature or textbook I have ever read are beneficial mutations required or even necessary for speciation. This is a key point: speciation doesn't occur due to beneficial mutations. Speciation (in sexually reproducing organisms, anyway) occurs when a population of a given species develops some type of reproductive barrier that prevents hybridization with the other members of the species. It can be a gradual thing such as an increase in hybrid incompatibility between populations over many generations. It can be a relatively rapid thing, where a sudden geographical separation and differential environmental pressures cause a barrier to gene flow so that after only a few generations even if the populations were reunited they are incompatible. It can be sympatric based on changing host specificity (such as occurred with Rigoletta, or some behavioral change necessitated by occupation of a novel or marginal niche, etc etc etc. Speciation has nothing at all to do with beneficial mutations per se, although those can "speed up the process" by natural selection culling the members of a new or marginalized population that don't have it. "Beneficial mutation" is a descriptive term that only applies to a genetic change which provides a net marginal fitness advantage in a given environment. IOW, by definition, it can only be detected after the fact. Whether a given mutation is beneficial, neutral or deleterious is a determination that can only be made in relation to the environment - which IIRC somebody already mentioned. Since as I noted above beneficial mutations do NOT have any direct relationship with the development of new species, your point here is moot.Hopefully this will get the discussion back on track. We now return you to your regularly scheduled discussion.[This message has been edited by Quetzal, 05-02-2004]