Darwin's theory relied on variation followed by natural selection. He didn't necessarily believe that the variation was random; that was a contribution of the "Modern Synthesis", combining Darwin with the findings of Gregor Mendel.
Cutting this a little short for now (so that I have something left to talk about): Evolution today is very different from what it was only a few decades ago. The revolution is largely the result of the rise of developmental biology, which is a merging of classical embryology, molecular biology, and the enormous amount of genetic information gleaned from the study of fruit flies (Drosophila melanogaster, for the nerds). This is something of a revolution in evolution, but few people seem to be familiar with it. So I am starting this blog, in which I hope to be able to describe the New World as I see it.
My undergraduate degree is in physics, followed by education in business and in software. I am almost entirely self-taught in evolution-related subjects. Evolution is the central organizing principle in astronomy, biology, and geology (to take them in alphabetical order). Part of the problem is that in order to get tenure in any of these subjects one has to go deeper and deeper into one of the many sub-branches of just one area. ("A specialist is someone who learns more and more about less and less, and winds up knowing everything about nothing.") Stephen Jay Gould wished that paleontologists knew more biology; some developmental biologists argue that evolutionary biologists should know some paleontology. I have never had a professional need to go deeply into any of the relevant subjects, so I have the luxury of being shallow in several. I'll try to tie them together for you.
Of course I get my information from other people -- books, journal articles, even other blogs :-) -- so I will probably misunderstand sometimes. Expert criticism is welcome.
So, the adventure begins.