[Petrochemicals (OP)]

Darwin theory of survival of the fittest is along the lines of those best suited to a situation survive, these qualities being carried forward and perhaps further increaced by the breeding animals having like qualities, as in the case of giraffes, long necked horsies breeding to produce even longer necked offspring. But how do these qualities come about in the first place? Long necked horsies had to gain their long neckedness from somewhere in the first place.

[alancalverd]

The DNA molecule is very "plastic" and can accommodate millions of random mutations, most of which are either benign (leading to healthy but different daughter cells at each replication)  or fatal (the cell does not replicate at all), with occasional malignant mutations (local tumors or grossly malfunctioning offspring). Sexual reproduction increases the probability of significant variation in subsequent generations of individuals. 

All that natural selection does is to apply environmental "filters" so that the ungulates with randomly-generated slightly longer necks can graze from slightly taller trees and within a few million years their progeny look so different that we call them giraffes.

Sexual reproduction can add another filter to that of external environment. Whatever philosophers might think (if they ever do), it is clear that all animals have a concept of "us and them", or "me and other", and generally express a preference for consorting and mating with "similar", whilst herd pressure tends to limit incest by driving out young or weak males, and solitary species effectively choose their mates from random encounters. 

To put it simply: it isn't simple. Reproduction throws the dice, but they are heavily loaded, there are lots  of dice, and very few winners.

[vhfpmr]

Mutation.

There are three foundation stones of evolution:
1)Mutation
2)Selection
3)Heritability

Mutations cause variations in the genome which get selected by the environment, then passed to the next generation.

There's no such thing as survival of the fittest, it's proliferation of that which is selected for (and loss of that which isn't selected for, eg: we've lost the genes that once enabled us to live off a raw diet because they haven't been selected for since we started cooking). There's nothing about a peacock's tail which makes it fitter, it just evolved because peahens developed an eye for it. The tail doesn't make it stronger, it merely advertises to a prospective mate the strength to carry an additional burden, which is why it's known as the Zahavi Handicap Principle.

[Petrochemicals (OP)]

How are these mutations decided upon, is it the small tinkering on already traits to see what works, is it forced mutation through experience so for example longer necks are actively favoured by genes, forcing the mutation, or is it random, in the way that so many births exhibit a certain trait.

[alancalverd]

Cart before horse! Mutations determine appearance and behavior, and individuals with beneficial mutations have a better probability of surviving and reproducing.

[Bored chemist]

How are these mutations decided upon

Since PC has declared himself too stupid to listen to me, it fall to someone else to introduce him to  Lamarckism.
https://en.wikipedia.org/wiki/Lamarckism

[Kryptid]

How are these mutations decided upon

They aren't: DNA doesn't "decide" which nucleotides failed to be copied properly.

is it the small tinkering on already traits to see what works

This implies that mutation and natural selection have intention, which they don't.

is it forced mutation through experience so for example longer necks are actively favoured by genes, forcing the mutation

Mutations aren't forced, but I think the probability of a mutation in any particular gene can be influenced by methylation, which in turn can be influenced external stressors.

or is it random, in the way that so many births exhibit a certain trait.

This is closer to how it works, although some mutations are more likely than others. Particular parts of the genome that can't tolerate mutations are better protected by repair mechanisms, so they are less likely to mutate than other regions.

[Eternal Student]

Hi.

    The main details for natural selection have already been presented.    Most DNA alterations are just random mutations  etc.

    I haven't studied Biology for years but this was one of the more "funky" or convention-defying contemporary ideas that was discussed back in the day.   It's useful to suggest that your DNA doesn't always dictate what you do, sometimes it can be the other way round....

    There's a small chance that DNA transcription to produce proteins isn't always a one-way process.   There are viruses with RNA reverse transcriptase enzymes so that RNA can be converted to DNA.   This opens the door to the possibility that information may sometimes flow in that direction from RNA to DNA which might then get incorporated into the nuclear DNA of the cell.
     Lets take a simple model:   A host organism has a physically demanding environment in which it must survive and to do this it is using a lot of muscle and this exercise is building more muscle in the usual way.   This means there is a lot of RNA in the cytoplasm that encodes for muscle proteins.   If a virus gets on board, some of that RNA can be reverse transcripted into DNA which could end up getting incorporated into the nuclear DNA stores.  The host organism now has two (or more) copies of the gene encoding for the muscle protein, so they are likely to get a higher transcription rate of RNA encoding for that protein from then onward.  This means there has been a permanent change in the amount of muscle protein the organism will synthesize - but, more importantly, if that change has occurred in the germ cells of the organism then this change is passed on to future generations.
    The effect is minor, if it happens at all, but it's interesting.   It's the possibility that the actions of the organism during its life might influence the DNA.   The whole set of circumstances falling into place, like accidental incorporation into the nuclear DNA, would only be a one-in-a-million chance but that is precisely the sort of scale we're talking about for evolution over many years.  It probably isn't going to be the main route for evolution but it could be a boost to the process.

Best Wishes.

[Petrochemicals (OP)]

To

Cart before horse! Mutations determine appearance and behavior, and individuals with beneficial mutations have a better probability of surviving and reproducing.

and

How are these mutations decided upon

They aren't: DNA doesn't "decide" which nucleotides failed to be copied properly.

is it the small tinkering on already traits to see what works

This implies that mutation and natural selection have intention, which they don't.

is it forced mutation through experience so for example longer necks are actively favoured by genes, forcing the mutation

Mutations aren't forced, but I think the probability of a mutation in any particular gene can be influenced by methylation, which in turn can be influenced external stressors.

or is it random, in the way that so many births exhibit a certain trait.

This is closer to how it works, although some mutations are more likely than others. Particular parts of the genome that can't tolerate mutations are better protected by repair mechanisms, so they are less likely to mutate than other regions.

And I imagine,

How are these mutations decided upon

Since PC has declared himself too stupid to listen to me, it fall to someone else to introduce him to  Lamarckism.
https://en.wikipedia.org/wiki/Lamarckism

does this mean

random, in the way that so many births exhibit a certain trait.

[alancalverd]

Radiogenic mutations can be caused by H2O+ free radicals facilitating crosslinking errors during mitosis, with consequent distortion of one of the daughter DNA molecules. As life evolved on a radioactive planet, this is a fairly frequent occurrence and completely random. Chemical and biological agents can also promote transcription errors, and sexual reproduction induces a whole load of  randomish variations in subsequent generations.

[Bored chemist]

And I imagine,

Try reading..

[Petrochemicals (OP)]

But surely random mutations would render many many traits, with all probability of being absolutely useless. A million years of evolution could create many many numerous mutation, a very small ammount being useful. It does not seem like this is a viable process.

[Bored chemist]

It does not seem like this is a viable process.

Well... it doesn't seem that way to PC but, ask yourself; "how clever is he?".

[Kryptid]

But surely random mutations would render many many traits, with all probability of being absolutely useless. A million years of evolution could create many many numerous mutation, a very small ammount being useful. It does not seem like this is a viable process.

Is that just your intuition or do you have evidence that it isn't viable?

[Bored chemist]

But surely random mutations would render many many traits, with all probability of being absolutely useless.

In a way, that's why about a third of us get cancer.

[Petrochemicals (OP)]

But surely random mutations would render many many traits, with all probability of being absolutely useless. A million years of evolution could create many many numerous mutation, a very small ammount being useful. It does not seem like this is a viable process.

Is that just your intuition or do you have evidence that it isn't viable?

Mathmatical probability. Random mutations would be far too erroneous. The theory of magnified traits would  be far too diluted if

So many mutations occour
So many percent of mutations where beneficial and not lethal
So  many beneficial mutations are passed on to off spring
So many offspring with beneficial mutations occur in a vecinity close to each other

Not that this is impossible, but for evolution to happen in such a small time frame of 50 million years to create such extremes of creatures from a common ancestor without destroying a species in the mean time is extremely unlikely.

[Kryptid]

Mathmatical probability.

Okay, show us the math.

[Petrochemicals (OP)]

Mathmatical probability.

Okay, show us the math.

1+2=3

[Kryptid]

Mathmatical probability.

Okay, show us the math.

1+2=3

You know, I would have thought that my question wouldn't need to be explained as if I were talking to a 5 year old.

[Bored chemist]

You know, I would have thought that my question wouldn't need to be explained as if I were talking to a 5 year old.

That depends if you are talking to someone who acts like a 5 year old...
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