MUtations can be deleterious, neutral, or beneficial in terms of the survival and reproductive fitness of the individual. The classic dogma is that most are harmful, but I’m not sure what the basis for that is. It may simply be the assumption that random changes in a complex mechanism are more likely to be damaging than not, or it may be base don some empirical data I’m not aware of.
The belief that mutations are usually harmful can be supported with reference to Second Law of Thermodynamics. Any random perturbation of a system is likely to increase its entropy. Perturbations that decrease its entropy are possible but rare.
To add a bit to the three very good replies - Most mutations are not even noticed; they just add to the variability of the species. If, later, the environment changes they may have some effect, positive or negative. Two I can think of are the HIV blocking mutation in Caucasians. Apparently about one in 140 have this. It was silent until HIV hit, and I doubt that it was doing anything else. The other is the sickle cell mutation that was more valuable in inhibiting the effects of malaria than were its negative effects, but became only detrimental when people moved away from that environment.
Was there something more to your question? There doesn’t seem to be much to discuss here.
All you need, macgyver, is one little “good mutation” (or a “memetation” :-) ) in somebody’s post and the thread will flourish. ;-)
You’re right George. Sometimes even the simplest question can trail off into very interesting tangential discussions. I was just interested in the thought process that resulted in the question. I thought that might add to the discussion if we knew what was behind it.
ie. Many ID proponents use the supposition that most mutations are harmful as “evidence” of how improbable evolution is.
If that conundrum triggered the question it might be helpful to discuss that here. Then again, maybe its irrelevant.
My guess is that most mutations are neither beneficial or harmful, simply neutral. An interesting hmm tagline for those sequencing DNA. Mutations don’t have a purpose (in their creation) they just are—-something that just happened to the organism.
I did some light searching, and I haven’t been able to find any reliable evidence for the probability of a mutation to be harmful, beneficial, or neutral. It seems that which you think most likely is determined more by where you stand of evolution vs ID more than it is by the evidence. I’d really be interested in any real evidence here, though I don’t think it’s the critical point int he evoluiton debate creationists seem to think it is. Even if the vast majority of mutations were functionally neutral or harmful in the environment in which they occured, that still would provide ample oppotuniryt for the development of new strructures and processes over the lengths of time and changes in the environment that occur. Lots of work has been done with bacteria and exposure to antibiotics, and it bears up quite well the argument that a low rate of deleterious mutations in a particular gene can be sustained in a population, and that a change in the environment (such as addition of an antibiotic) can make that mutation suddenly beneficial and very successful. So while it’s an interesting question, it doesn’t really rpovide any threat to the concept of mutation as the source of genetic variation upon which selection acts.
Even if many mutations are neutral, a random mutation is more likely to destroy than create something new, so it seems.
The word ‘mutation’ has negative connotations although it is either a neutral event, or reaction to an organism under environmental pressures. Think of the word ‘evolve’. They both mean essentially the same thing, but we think of evolution in a positive sense. In order to evolve, an organism goes through mutations. All evolution is mutation.
I’m not sure it would be easy to find the type of factual evidence on this question that you were searching for McKenzie, but on a purely theoretical basis I would expect most mutations to be neutral. The biology of DNA is such that vast stretches of it seem to be relatively “silent”. These stretches used to be called junk DNA implying that they served no purpose. The truth is turning out to be a bit more complicated, but it still seems that most of these sections can change pretty dramatically before having much of an effect on the organism.
Within sections of DNA that code for specific proteins, the majority of mutations will most likely be either harmful or neutral. I’m not sure whether anyone has ever truly done an analysis of this to figure out which outcome will dominate in this section of the code, but many mutations will have no effect on the amino acid sequence of the final protein because of the redundant nature of the DNA code. Even mutations that do change the sequence will not necessarily change the structure or function of the final protein. Obviously mutations that have a net beneficial effect to an organism will make up the smallest percentage of the total.
When all sections are taken into account, I think we will find that most mutations are likely to be neutral in their effect.
Even if more mutations are harmful than are helpful, that really doesn’t prove anything. All organisms die, and almost all by accident. If I spray insecticide at a fly quite purposely, it just happened to be in the area by accident, just as some other fly that remained outside didn’t happen to be killed a that moment, and a third may have gotten hit by only a sublethal dose of insecticide so is just disabled. Similarly, some genes get degraded by a reaction with some chemical, being zapped by a cosmic ray, by radiation, etc. It’s just one more way that organisms move toward death.