Complex thoughts need grit-y minds to unfold in. They need to be attacked from multiple perspectives. They need to be nurtured at the point where we're most likely to let go. They need to be played with. And they need different mind spaces to be understood inside and out. Good cities like Cambridge help these ideas to unfold through Brownian motion. Minds drift towards each other. They meet one another and form conspiracies with one another.
Franklin noticed a conflict in her data. There were two kinds of DNA that she had discovered along with her partners; what they called "A" and "B". One was a strand without water that was crumpled together. The second was with moisture that was long and thin. Franklin chose to study type-A and her work led her to suspect a helix was present but she was reluctant to commit to the idea as she was sceptical of any model. Through sheer happenstance, Crick and Watson knew her colleague and were working on a theoretical model for the same, eventually leading them all to use this data to - in a haphazard, chaotic way - lead to an understanding of DNA.
Someone might have discovered DNA sooner or later but if everyone hadn't been present in Cambridge at that moment in history; it would have definitely been later.
Greatness needs serendipity. And serendipity needs the machinations of probability. And probability needs humans to drive the gears.