It's mainly to do with the discovery of genetics and how that influences natural selection (which of course Darwin knew nothing about through no fault of his own). Some articles you may wish to read:
http://en.wikipedia.org/wiki/Natural_sel...evelopment
http://en.wikipedia.org/wiki/Modern_evol..._synthesis
http://en.wikipedia.org/wiki/History_of_...ry_thought
Again, with the theory of Evolution, nothing has really changed with the general idea, (that nature selects the beneficial traits). What has happened is that genetics has opened up the explanation of how it all happens.
http://en.wikipedia.org/wiki/Natural_sel...evelopment
http://en.wikipedia.org/wiki/Modern_evol..._synthesis
http://en.wikipedia.org/wiki/History_of_...ry_thought
Again, with the theory of Evolution, nothing has really changed with the general idea, (that nature selects the beneficial traits). What has happened is that genetics has opened up the explanation of how it all happens.