(Original post by zimzim40)
Hi, I'm very confused. What is Natural Selection? and What is evolution?How are they related? and what evidence is there for it?
Technically, what we call "Evolution" should actually be called "Evolution by natural selection". Evolution is simply a change in something's characteristics or parameters, and it hasn't got a purely biological meaning. "Natural Selection" is the process by which the Evolution we are talking about happens, hence the term "Evolution by natural selection". Evolution is what is happening, and natural selection is the process by which it happens.
Natural Selection is essentially the idea of "Survival of the fittest". As a result of sexual reproduction and/or genetic mutation, there is naturally genetic variation within a population of living organisms. Often, most of the variation is irrelevant but sometimes the variation has an impact on the organism's ability to survive and reproduce. The organisms that are more successful at surviving and competing with other organisms are also more likely to reproduce and thus pass these genes on to offspring, so the 'fitter' genes are naturally selected for. We can use an example to illustrate this. Imagine we have a plant which is constantly being eaten by animals. Since most of the plants are eaten, they can't reproduce and therefore most of them are unable to pass on their genes. Imagine a random genetic mutation in one plant means that its leaves suddenly synthesise a protein that is poisonous to the animal that eats it. Because animals are less likely to eat this plant, it is more likely to survive and pass on its genes. Over time, its population will increase at the expense of the plants that don't carry this poison-synthesising gene, so we say that this gene (or new species) has been naturally selected for.
There is a massive amount of evidence for evolution and I couldn't possibly go through all of it here. Firstly, it's kinda common sense to a certain extent - it's pretty obvious how this allows successful genes to propagate. It's a logical process that would naturally occur because it works. Obviously though, we need evidence and there's plenty of that. The fossil record, whilst not complete, shows the kind of gradual change that we would expect from evolution. You can also extrapolate evolution from current observations, as is the case with Darwin's finches. Darwin noted that the beaks of finches varied between islands depending on what food source was available, i.e. finches on islands with nuts and seeds tended to have hard, strong beaks and finches on islands with insects had long, sharp beaks, etc, which is explained by evolution. A good scientific theory allows you to make predictions that describe the natural world accurately, and evolution does this perfectly. Evolution is a slow and gradual process but it has actually been observed in labs through experiments on bacteria. A kind of evolution can also be seen through the seasonal flu variations and the antibiotic resistance of certain pathogens such as MRSA.