Random mutation or environmental factors?

[Anarchaus]

Hi I was wondering, why do creatures have to evolve by random mutation?

The odds of a random mutation actually occuring are low, and the odds of it actually helping the organism in a certain enviroment are exceptionally low.

There must be some mechanism that causes the actual mutation, so why can't it be due to a change in the enviroment? would that be enough to alter the organisms genes?

[Skye]

The odds of a random mutation actually occuring are low

Not really. DNA is fairly unstable and there are alot of things that will react with it causing mutations, but you have a variety of repair processes that reverse these mutations. These don't catch all the faults though, so there's still a fair amount of mutating going on.

 

Things like bacteria don't have nearly as sophisticated repair mechanisms so they mutate at a greater rate.

the odds of it actually helping the organism in a certain enviroment are exceptionally low.

Yes, but with a higher mutation rate this isn't such a problem.

There must be some mechanism that causes the actual mutation

Yes, there are many. Thermal degradations, chemical reactions, photochemical reactions, probably others I can't think of.

so why can't it be due to a change in the enviroment? would that be enough to alter the organisms genes?

I don't think it's impossible, however I haven't seen any good evidence that it occurs.

[Anarchaus]

Oh,so your saying, that foreign factors actually cause the mutations, such as the enviroment, but it relies on random sections of the DNA to be changed to actually benifet the organism.

 

So if a microbe is in a foreign enviroment, and it happens to be cold. The enviroment damages the DNA, and the microbe trys to repair. And lets say by chance, the part of the DNA required to regulate the metabolism is damaged, and the mutation causes it to speed up then the microbe can survive to reproduce? Is that how evolution works?

[Hellbender]

Actually, both. Naturl selection is the environment acting on random mutations.

[Skye]

Oh' date='so your saying, that foreign factors actually cause the mutations, such as the enviroment, but it relies on random sections of the DNA to be changed to actually benifet the organism.

 

So if a microbe is in a foreign enviroment, and it happens to be cold. The enviroment damages the DNA, and the microbe trys to repair. And lets say by chance, the part of the DNA required to regulate the metabolism is damaged, and the mutation causes it to speed up then the microbe can survive to reproduce? Is that how evolution works?[/quote']

Yes. However, remember there are many things that are inside a cell that will cause mutations though (cells have many different chemicals) and DNA is unstable, it falls apart on its own. So there doesn't need to be an environmental factor there to cause the mutation.

[Sayonara]

And it's important to realise that this can happen in any cell in any individual - so it's really not "uncommon" in population-wide terms.

[Xavier]

A lot is going on to make functional changes to a population of creatures through natural selection. For a start, within any population there may be several different sequences of DNA(genes) at each particular place on each chromosome which exist in different combinations in different individuals of the live population(the gene pool). In a stable environment several combinations can exist that give the same overall inclusive fitness by slightly different means. When the environment changes, different combination may become more beneficial. Situations can arise where too extreme or prolonged environmental change makes the gene pool sparse as there are no more combinations of genes that can increase survivability and this is one of the reasons supposed for species extinctions occurring (i.e. pressure from a new predator makes grazing animals need to run faster. The sheep-like creature and the pig-like creature are both undergoing natural selection for longer legs and bigger leg muscles but, whilst the sheep can just need a lengthened femur and built-up rump, the pig would need a reshaping of its hip which has been a part of its body architecture for so long that there are not sufficient options in its population of genes - there are too many other genes that only work with a standard pig-shape that bearers of any other gene wouldn't survive - so the pig-like creature dies out)

Mutations creep into the genepool with time if it doesn't have a negative effect on inclusive fitness and whilst the enivronment is stable the diversity of genes that combine to do roughly the same job of making a surviving creature increases. This is an aspect of the widely, though not universally accepted theory of punctuated equilibrium in evolution.

 

Amongst animals that use sexual reproduction there is a mixing of genes where pairs of chromosomes come, one from each parent and before that each chromosome is also spliced and rejoined so that the chromosomes received from your mother will derive from parts of those she got from each of her parents. Each gene therefore gets mixed up with a different set of fellow genes in each new generation. However, genes that are close to one another on the same chromosome will stay together unless the splice happens to fall between them so they are likely to be together for several generations.

This allows genes to evolve in groups that are mutually dependent. Various activities can cause genes to change their place on a chromosome and when two genes that happen to complement each other (ie. increase inclusive fitness of their body) happen to move close together and thus be more likely to be together again in the next generation will tend to remain together. They could become so necessary to each other that it makes more sense to describe them as a single gene.

 

Amongst humans (in this case the choice of humans as an example is due to that species being studied far more intensively than any other - one presumes the same to apply in other species) there are many areas of the DNA code that are apparently unused. There are many ideas for why it is there and just one of them is that it is left over genes that are no longer used. This idea is bolstered by other bits of our genome that appear to be genes but which never get swithched on and still others that do get switched on but then either get immediately interrupted or the code is read and then the mRNA which transports the code is disposed of, rather than sent off to be processed. There may well also be some proteins amongst the thousands that remain unidentified within our cells that are made by genes but which no longer have any effect at all. These all appear to be different stages in the removal of DNA code that is presently surplus to requirements.

There are legion examples of proteins (eg. melatonin, a byproduct of hormone building that is now used as a sun screen) processes (sneezes and coughs have been developed into audible communications in some animals) and whole body parts (our lungs may have begun as buoyancy bladders in fish?) that have apparently found new uses presumably because something that hadn't been removed from the genepool during the random shuffling of DNA just happened to slightly improve inclusive fitness in a new environment or in combination with a new gene.

 

I haven't even mentioned the newer ideas about evolution in the gene expression control mechanisms. The take-home message is that the mutations that give a beginning to the whole diversity of life may be random and beneficial mutations may appear extremely unlikely (in fact computer simulations and 'creation in a bottle' experiments have shown that there is time to spare. Punctuated equilibrium came, in part, from the question of how come evolution took so long to get to us) but they is a lot of complex meachinery working to make the best possible use of it.

As far as the genes are concerned, if they had concerns at all, mutation would be death.