Well, SoSick, all you need to do is look around you: there are no organisms that do not change hereditary traits from generation to generation. This is evolution.

That evolution occurs is a fact, and it has been demonstrated any number of times.

We can also look at genes and see the same relationships of comparable genes that we do with closely related relatives and more distant relatives. Aunts and Uncles show fewer similarities than brothers and sisters but more similarities than strangers. The same pattern holds for species, with closer related species having more similarities than more distantly related species.

These genetic patterns can be used to make phylogenic trees showing those relationships. This genetic pattern can be done again and again and again by different groups of scientists in different parts of the world in different labs, and they end up with the same phylogenies. Thus these results are repeatable.

We can compare these phylogenies with the ones developed over the last 200 plus years by taxonomists and see - surprise - that they are by and large the same, over 90% consistent, but that there are some differences. Those differences become things to research in greater detail rather than avoid, as creationists would have you believe (especially those who think evolution is a conspiracy of falsehoods), rather they are cause for excitement.

We can look at these multiple methods and reach the same conclusions, not because there is a conspiracy, but because it is what the evidence shows, it is the truth.

Can I prove that the theory of evolution is true? No, but that is because no theory can be proven true, not one, not in any science.

Does that mean there is no standard of proof? No need to validate the theory? No, it is just that the standard of proof is that the theory is valid, rather than that it is absolutely true, and this standard of validation is the same as in any science: you need to test the theory, continually, and try to disprove it, try to show that it is invalid or results in contradictory predictions.

This is done, it is done by biologists every day. The test is that evolution explains all the evidence, not just the evidence that conveniently fits the theory.

So far, after over 150 years of trying to disprove Darwin's theory, descent with modification, it has not yet been falsified by a single piece of evidence. Newton's law of gravity was falsified, and replaced by relativity, but Darwin's descent with modification is still a valid theory.

We have added processes and increased our understanding of how variation occurs, we have found the basis for hereditary traits and determined how they can - and how some traits cannot - be inherited by offspring.

We have found thousands and thousands of fossils since Darwin's time, and in no case is there one that falsifies the theory or contradicts it, rather the fossils keep sorting themselves into phylogenic trees of relations, relationships that are valid in time and space, and that show a pattern of descent from common ancestors.

We have seen actual instances of speciation, where one population of interbreeding organisms becomes to daughter populations that no longer share genes, and begin accumulating different hereditary traits. We have seen breeding isolation occur from something as simple as a different mating song and some minor color changes.

Speciation is all that is necessary for a phylogenic tree to branch, to split into two or more different lines of descendant species.

I can show that the degree of variation that we see in dogs is sufficient to explain the morphological differences between species as one species supplants it's ancestral species and is in turn supplanted by it's descendant species: the morphological differences are less than that from wolf to dog.

I can show that in 60 years a line of dog-like foxes can be bred from an isolated group of russian silver foxes by the sole mechanisms of breeding isolation and the selection for a single trait: lower fear or anxiety. These dog-like foxes show the same kinds of morpological differences in size, and in proportions, that we see in fossil records between successive species.

I can show that an initial population of 50 to 100 starlings introduced in NY city has resulted in the millions of starlings that infest North America from coast to coast in as little as 50 years, thus demonstrating how a new species that is successful can quickly spread into new ecologies.

I can show intermediate fossils, some for birds, some for mammals, some for quadrapeds, that again all show a general pattern of (1) evolution within populations and (2) speciation and division between populations, and that this is sufficient to explain the natural history of life as we know it, from today, from history, from the natural history of fossils and geology and from genetics.

I can demonstrate that evolution can explain the natural history of this planet, and that is what theories do: they provide explanations, explanations that are tested by reality, and explanations that are the closest we know to the truth of what really happened, and I can show that they are feasible.

I am sorry that reality is hard for some people to swallow. Scientists are used to this, as many experiments end in failures when reality does not match hypothesis. But the difficulty in swallowing is not because of the validity of the concept: reality is true no matter what you believe.

That the evidence of reality keeps contradicting belief is not my fault.

The earth is at least 4.5 billion years, that is a fact, it is a fact because there is evidence that is 4.5 billion years old.

The universe is at least 13.7 billion years old, that is a fact, it is a fact because there is evidence that is 13.7 billion years old.

Life on earth is at least 3.5 billion years old, that is a fact, it is a fact because there is evidence that is 3.5 billion years old.

These ages are not determined by evolutionary biologists, but by geologists and physicists, people that could not care whether we are descended from apes or not, but in understanding their particular interest in objective reality

I can prove that the theory of evolution is valid by the simple fact that there is not one piece of evidence that contradicts evolution to date.

The standard for scientific theories is that they provide the best possible explanation for all the evidence, and that the theory be tested repeatedly for invalidation, that there is no contradictory evidence, and that there is no better explanation currently known.

Evolution meets this standard.
Creationism does not.

To discuss how evolution explains diversity I suggest this thread - Evolution Theory Explains Diversity

To discuss how the ages of certain things stack up in reality I suggest this thread - A Well Aged Earth


Enjoy.