You honestly think it was "human development" (aka evolution?) that got it to sub 4:00 and sub 10? Trust me, there was no human evolution between 1940 and 1954 let alone "human development" within John Landy who was unable to break 4 pre-Bannister but was able to do so three months afterwards.
It is an open question whether in perfect conditions (which don't describe any big city marathon but which track races come a lot closer to), any of the world's best current marathoners could run 2:00:00 for 26.2. Bannister only had to find 1 second but all previous records had been set in conditions very similar to those he ran in. No-one has attempted to set up a truly optimized marathon before - this is new territory.
Ok, sorry about the caps. I get excited. Yes, I do think it was human development. The human body changes from generation to generation so considering how close they were to 4, yes I think in 15 years they got a little closer and were finally able to break it. Where was the 100m 15-20 years ago? It has gone down. Now not by much, but considering of how short of a race it is, I believe it did progress because people were getting stronger and faster. The problem with this is that a couple minutes in the marathon is going to take about another 15-30 years.