I reckon the whole 'evolution throughout time' is a pretty moot point IMO. There is absolutely no way to tell how Bradman would fare today if he'd been brought up in the modern era with the modern game, and similarly no way to tell if a modern player would succeed if he were born and raised in the 1920s.
To put this in international relations (namely realist) terminology, since I have no other way to really express it, nobody gives a **** about absolute ability. If everyone's special no one's special. What matters is your ability relative to those around you.
So yes, every player in the modern era may, in absolute terms, be significantly better than Don Bradman. But you have a long list of blokes averaging around 50 that are the premier batsmen of the day - nobody stands out from the crowd by a hugely significant margin (on any given day, form notwithstanding, Amla = Cook = Clarke = de Villiers = Pietersen = Smith = Kallis = Tendulkar = Hussey or thereabouts). So in terms of relative ability, the top batsmen of today are remarkable close.
Let's apply this to the 1930s and 1940s. More-or-less, Hutton = Hammond = Headley = whoever else you want to throw in the analysis, but Hutton/Headley/Hammond definitely ≠ Bradman. In absolute terms, you can argue quite readily that Bradman is not as good as Tendulkar because of the evolution of the game and whatnot, but in relative terms, Bradman is that far ahead of anyone else that he is clearly the greatest.
Absolute ability means nothing if you have nothing to compare it to. It takes on value in how it stacks up compared to peers.
So in an ATG selection context, you look at who had that much relative ability compared to their peers, and use that as a measure of greatness - otherwise there is a huge argument that an English ATG XI would look like this:
Cook, Strauss, Trott, Pietersen, Bell, Flintoff, Prior, Broad, Swann, Anderson, Hoggard
simply because the game has evolved since 2000.
