I was discussing at another site on the theory of evolution and I wrote the text below. I found it interesting to post here to receive feedback to improve it, and also assist other people in similar discussions.
Here it is:
Evolution is a fact, and there is a theory to explain it. If someone doesn't agree with the theory of evolution he should show some other better theory for this fact, or at least show some evidence that contradict the theory. Denying evolution itself is ignorance, it's just like denying gravity. There is a theory for gravity, you may don't like it, or don't understand it, but can you deny gravity?
So how evolution is a fact? Let's first read a definition of "fact":
"A fact is a hypothesis that is so firmly supported by evidence that we assume it is true, and act as if it were true."
That seems right. At least it's way better than definitons like "a fact is a fact".
Ok, and how about looking into some evidences of evolution?
1. The genetic of the current living beings: humans have 96% of genes in common with chimpanzees, about 90% of genes in common with cats, 80% with cows, 75% with mice. All life on earth shares some basic aspects through the DNA. This is an strong evidence of a common ancestor, but this one alone could not be enough to sustain the theory. So, let's keep going.
2. Fossils: there are not human bones dating from longer than 6 million years ago. Dinosaur bones dates from more than 60 million years. In the middle we have a huge variety of species "appearing" and "disappearing" with small changes along the centuries. Can you guess why the fossils analysis suggest evolution? Well, what would be the other explanation, a super-ghost manually interacting with life on earth to create new species century by century?
3. Current evolution. A butterfly had evolved in front of our eyes: http://en.wikipedia.org/wiki/Hypolimnas_bolina#Recent_evolutionary_changes
. And there are other examples, including evolution tested in a controlled environment: http://myxo.css.msu.edu/ecoli/index.html
People may try to deny the science used to reach those evidences, like: "DNA do not exist", or you "guys can't read correctly the age of this bone". Interesting how those people don't try to study about that. Imagine if you could show to everyone DNA is a lie. You would be awarded with a Nobel Prize. Or if you could prove the methods for dating fossils are wrong, you would gain a lot of respect and probably money. It's also funny how people who deny this science make use of microwave ovens, GPS, go to doctors and take drugs, and so on. How much science there are behind our daily lives? How convenient it is to only accept the science that does not contradict your holy book?
Another important thing to understand in this debate about "god Vs evolution" is to take a look at the motivation of each side. Religious people were told to believe (by people they respect a lot - like parents) in some sort of things. When someone claims that these things are wrong, it may look like they wasted a good portion of their lives in a dumb fantasy, and the people they respect a lot are in fact wrong. This creates a resistence that can block logical arguments and evidence analisys. Science on the other hand just seeks for the truth. Science do not have special protection for some particular theory, it is always open to new input and self-correction. But you have to come with some observable evidence, and some logical argument, not just "it's written in a holy book".