Are mutations enough to explain natural selection?

Let me begin by saying that I am an evolutionist. I understand that if a mutation is favourable to an organism, that organism will tend to produce more offspring and the mutation will spread. But surely most mutations (apart from the odd useful macromutation) wouldn't help an organism so much that it increases its chances of survival or reproduction.For example, if a mutation gave a bird a slightly longer wingspan, the bird might fly more efficiently and catch more food, but does this ensure that the gene for long wing is passed on more than the gene for short wing? A bird that caught 9 fish a day would probably reproduce just as much as a bird that caught 10 fish a day.Perhaps natural selection is only effective when resources are limited and even slightly helpful mutations mean the difference between life and death, or between reproduction and lack of.Thoughts?------------------
"I'm rather less interested in what people think than in what's true"
- Richard Dawkins

Let me use another example that doesn't involve competition. How would natural selection favour a slightly larger skin flap in colugos, gliding possums, etc if an advantageous mutation merely allowed an individual to glide an extra metre?------------------
"I'm rather less interested in what people think than in what's true"
- Richard Dawkins

quote:

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Originally posted by Fred Williams:
The rate at which a mutation can fix in a population is governed by its capacity for reproduction.

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I understand that. The more advantageous a mutation is, the more likely the carrier of the mutation will survive to reproduction.

quote:

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Originally posted by Fred Williams:
The only way to reduce this number is to increase the selective value, but when you do this the burden on reproductive capacity increases!

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That's what I don't understand. Please help me out.
I apologise if this seems like a stupid question because it's obvious that most of the people on this forum have a greater understanding of this than me but I really want to understand how this works.Thanks.------------------
"I'm rather less interested in what people think than in what's true"
- Richard Dawkins

quote:

---

Originally posted by Fred Williams:
The rate at which a mutation can fix in a population is governed by its capacity for reproduction.

---

I understand that. The more advantageous a mutation is, the more likely the carrier of the mutation will survive to reproduction.

quote:

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Originally posted by Fred Williams:
The only way to reduce this number is to increase the selective value, but when you do this the burden on reproductive capacity increases!

---

That's what I don't understand. Please help me out.
I apologise if this seems like a stupid question because it's obvious that most of the people on this forum have a greater understanding of this than me but I really want to understand how this works.Thanks.

Thanks Fred for your clarification and everyone else for the responses. Your answers have been very helpful but to keep the discussion going and to stop the topic straying too far into areas I am not very familiar with (I again apologise for my shortcomings) I would like to reiterate my original question:How does natural selection favour a mutation that, while advantageous, is not likely to increase the carriers chance of survival or reproduction.For evolution to work, every transitional step between, say, the light-sensitive skin-patch and the human or cephalopod eye has to be not only advantageous but advantageous *enough* to increase the individuals chance of reproduction. I sometimes have trouble seeing how that could happen, but I suppose it's like Gzus said and every time an adaptation evolves the situation is unique, so there is no single answer.As for the Dawkins quote, I didn't read it, it's from a television debate, and I agree that you don't need a great understanding of genetics to understand evolution. Darwin is proof of that. Besides that, I admire scientists that are comprehensible and interesting to the layman and I think Dawkins fits this category.