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Is genetic variation the raw material for evolution?

How is variation maintained for evolution?

  • For example, how was the variation maintained for the natural selection which led to an increase in giraffe neck length? I know, to start with they'll be some variation and if those with the longest necks were selected, the average neck size would increase. However I can't see how the neck length can substantially increase because surely they'll become a point when the "long" genes have spread around the population.. then most giraffes have the same neck length. How can they evolve even bigger? In Richard Dawkin's Selfish Gene, he says this is not a problem because natural selection rarely acts in such a biased directed way. But then how can the giraffe neck evolve?

  • Answer:

    your idea would be correct if genes never would change. But mutations exist and can make new genes. Or have old genes expressed in a different amount or a different time, which can also make a large difference in how strongly they are expressed in morphology (e.g. a large peak in growth hormone when there are also a lot of receptors in tissue present will give different results than if there is barely any receptor around). But if genes never would change or get rearranged, then we wouldn't get new species either, just variants. Though you only have to look at dogs as an extreme example how different variants of the same species can be.

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Although it would seem that after a long period of time veery giraffe would have the same length neck - but the changes would obviously happen gradually. It's all about survival of the fittest. The giraffe was having to compete with other animals like elephants and antelopes to get the same food, so they would obviously need to change because their species was dying out. The main this is that they would stretch, and little by little over many generations the change would occur. Now when all the giraffes have the same length neck, the process would start again. It was longer, but not long enough to compete with the other animals. They would stretch a little more until one giraffes beck would be again slightly longer, then the gene would be passed throughout the species exactly the same as the first time. This took an extraordinarily long time - but after this process was repeated, the giraffes neck was long enough to reach food that no other animal could.

Alis *x

Hypothetically, when most the giraffe necks are the same size (though natural selection), several giraffes may be born with a mutation to have even longer length necks and then through natural selection the population of giraffes have longer necks due to the need to reach higher branches in trees. This would continue until today. Edit: Lol at Alis's answer below. Nothing to do with stretching. All to do with random mutations and natural selection / Survival of the fittest as she stated

Fragile

At conception, a fetus' DNA mutates providing new traits and increasing variation. Chances are that within a species, some will develop longer necks while some will develop shorter necks than their parents.

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