Can you give any evidence for Darwin's theory?

[Sejanus]

Ok, most of you are giving examples of evolving in little ways. I should have clarified this but i am talking about a change of kind. IN the case of evolution some people think a fish or a monkey to a human. Do you have evidence of a change of kinds like a fish to a human, or a monkey to a human.

Don't ever use that word when discussing evolution. Ever. Here's a little crash course in high school evolutionary biology. First, let's define the word species. A species is a population of animals that can successfully interbreed to produce fertile, viable offspring. Next, I'll inform you that all individuals in a population show some variation in their genetic make-up, which may or may not manifest itself phenotypically; what the animal looks like. It's the reason you don't look exactly like your parents. This variation comes from - Mutations, crossing over and recombination of chromosomes, among other things (I haven't looked at my High school Biology texts in like, a year, so if this isn't sufficient I will explain the variation in more detail).

So, now we have a population of individuals of the same species that show genetic variation and can successfully interbreed to produce fertile offspring. Big whoop. To produce a new species, mechanisms of speciation must act on the population. There are a whole host of these, so I'll explain one that's easy to understand. Allopatric (means "other-land") speciation occurs when a group of individuals is separated from the main population of the species by some geographical barrier, like a river, a new mountain range, etc. The climate is likely to be different where the small group ends up. As such it will have different selection pressures than the original environment. Remember, the group of individuals shows variation, so those individuals who can best adapt to the selection pressures in the new environment have a better chance to survive to pass on those genes that helped them survive. Hence, over many generations, the group develops similar traits which are best suited to surviving in the environment they live in.

To explain this, I'll give an example. Suppose there is a population of mostly green lizards that was located in a forest. A small group of them end up in the desert, where the colour of the sand is yellow. Birds of prey can easily spot the most green lizards, but have a harder time spotting ones that have a colour closer to yellow (due to variation). The yellow-ish lizards will therefore be more likely to survive, to be able to reproduce and pass on their genes. So the group becomes mostly yellow-ish over time. Which leads me to speciation. Say those yellow-ish lizards make it back to the forest. The original population of green lizards will now not be able to recognize the yellow-ish lizards as potential mates; i.e a post-zygotic reproductive isolating mechanism has developed. (there are many of these, this is just an example. There are also pre-zygotic reproductive isolating mechanisms; a different number of chromosomes, for example, among others). Now we can go back to the original definition of a species; a population of animals that can successfully interbreed to produce fertile, viable offspring. The yellow-ish group do not breed with the original population, and so mutations and other RIMs develop to the point where they are unable to interbreed successfully with the original population. This is the point where a new species has developed.

In order to get your "fish to a human" scenario to happen, there needs to be hundreds of thousands if not more of these speciation events, through billions of generations. I hope I've shown that evolution by natural selection explains how you will never see a fish evolve into a human in one generation, the timescale required for that to happen is geological; in the order of billions of years.

Evolutionary biologists of the forum: feel free to correct me.
Creationists: take notes.