KeithHarwood

(I've just had a thought. Sorry if this is teaching grandmother biologists to suck eggs, but I've never come across it and obviously the creationists have never heard of it.)

Creationists twitter on about change and randomness of mutations and how that can't possibly lead to useful changes. They might be right. However, it seems to me that chance and randomness don't come into it.

Mutations are random so for a single individual, the chances of a particular mutation occuring are very small. However, for a large population over a long period of time practically all mutations will occur, so it is inevitable that a particularly advantageous mutation will occur. The only random thing is which particular individual it will turn up in.

What's more all possible advantageous mutations will occur, so all possible strategies for population expansion will be tried. If some strategies are mutually exclusive speciation is inevitable. Chance has nothing to do with it.

(OK, you professionals out there. Do I get a Nobel prize for this or a smiley stamp on the back of my hand? Or do I get an F and told to go back and revise my statistics?)

Edited to add:
Chances are that Fischer sorted this out in the 1920's, but I've never seen it written down.

[ May 11, 2002: Message edited by: KeithHarwood ]</p>

Brad Messenger

As Dawkins once noted, mutations are regarded as chance events only relative to natural selection. They have natural causes are not truly random. Mutations to the individual may be bad, but to the species they are essential for survival.

Firstly, mutations occur all of the time and most are caught during proof-reading with only a few slipping through the cracks. Each person, I think, have many mutations that usually don't cause us harm, though they may down the road.

On the species level, mutations are only helpful. Any individuals with harmful mutations are wiped out by the next generation and so for each generation you are, in case all mutations were bad, with the non-mutated organisms. For the many mutations, though, that are harmless in the present environment, they could become useful given the dynamics of the environment. Thus, mutations, many of which are harmless, increase genetic variation within a population and thus helps the species.

We hear about individuals hurt by mutations and those who are not harmed by them, the rest of us, just assume these unfortunate cases are the norm. Natural selection ensures that mutations, though unexpected errors in replication, they provide a long-term benefit to the species and unfortunately sometimes harm to individuals.

tronvillain

Well, it's probably not true that on the species level mutations are only helpful. It is entirely possible for a "deleterious" allele to become fixed in a population.

Brad Messenger

Tronvillain,

I agree and I'm guilty of making a statement too strong to be true in order to emphasize a point. A mutation may not show itself in an individual's phenotype and yet ride the "coattails" of a beneficial mutation or in a favorable genome. Once this genotype has spread throughout the population, the environment changes and the hidden, harmful mutation expresses to the detriment to the population. This would be similar to mutations that are harmless now and become beneficial in later generations. Of course, if other mutations come into population, there may be the variablity to combat the harmful mutation when it is finally phenotypically expressed.

liquid

IIRC, one of Dawkins' books has an estimate of three to four mutated genes per person on average.

Synaesthesia

It's also important to remember who's good we're talking about. Some mutations that are bad for the individual, bad for the populations will spread. Ideas bad for the world, bad for the individuals can also spread.

tronvillain

Brad Messenger,

Even deleterious alleles that do show themselves in an individuals phenotype and don't ride the coat tails of a beneficial mutation can spead through a population. Don't ignore genetic drift!

Peez

Just for fun:

Over the past few thousand years (except recently), it has been estimated that the human population of this planet has hovered around 150 million. Let's be conservative and go with 20 years per generation, so there have been about 250 generations over the past 5,000 years. If each person born had about 3 mutations, there have been over 100 billion new mutations in humans over the past 0.005 million years.


Peez

joshack

Brad,

Could you please explain what you mean by these two sentences?

Thus, mutations, many of which are harmless, increase genetic variation within a population and thus helps the species.

Natural selection ensures that mutations, though unexpected errors in replication, they provide a long-term benefit to the species and unfortunately sometimes harm to individuals.

Brad Messenger

Question (1): It has been noted by an earlier poster that there are 3-4 mutations for each individual. I was told in high school by my biology teacher that it was a 1000 mutations per person, but in either case it means that mutations are common in animal life and not automatically harmful as it is generally thought.

Natural selection operates when genetic variation exists within a population. Mutations increase variation by creating unique genomes for individuals. Genetic variation makes it possible for a species to adapt to changes in the environment since some individuals, based upon their unique genome, would be better suited for one environment over another. So since mutations increse genetic variation and variation is an essential part of long-term survival for species, you could say mutations help the species. This is all basic evolution stuff that you probably already know.

For question (2), natural selection removes individuals with harmful mutations so by the next generation, the population only consists of individuals with non-harmful mutations. Thus, harmful mutations would hurt the individual but not the population or species. The benefit of mutations is, of course, the genetic variation. So mutations may be a disadvantage to an individual, but in the long run, it is beneficial by creating diverse genotypes.

I am only a student on the subject and by no means an expert. I may have ommitted some important details and I hope people revise or criticize this if necessary, as tronvillain has done for a couple posts.