[BroJoeK]

101ORD: "Isn’t ‘descent with modification’ natural selection?"

Thanks for the question.
The basic theory-fact of evolution is not really disputed by anyone on FR, and consists of two confirmed observations:

1. descent with modification -- offspring are often different in some ways from their parents.
   
2. natural selection -- some modifications are more helpful to survival than others, aka "survival of the fittest."

So, when people say, "evolution is a fact," this is what they are referring to.

It's the "grand theory of evolution" which causes so much debate -- namely that over millions and hundreds of millions of years, virtually all of life on Earth descended from common ancestors.
That can never be directly observed, of course, and must be inferred from literal mountains of evidence (the fossil record), plus input from virtually every other discipline of science -- from astronomy to physics, chemistry, geology, biology & on & on, now especially DNA analysis.

That's what they say is "only a theory."

But even that "grand theory" has been confirmed so many times the theory itself is no longer seriously debated amongst serious scientists.

[1010RD]

Thanks for your thoughtful response. Take a look here: http://www.wisegeek.com/what-is-the-simplest-organism-known.htm

That simplest living organism is incredibly complex. Was it simpler at some earlier period of earth’s history. I’m not bothered by the Theory of Evolution on a religious basis, but a scientific one.

How do you falsify the Theory of Evolution? What would definitively prove it wrong?