They had the 'natural gift' of picking up on the clues hinting that DNA, rather than protein, was central to the mechanism of biological inheritance. It is the natural gift of being able to identify the key features of the forest despite the preponderance of obfuscating trunks and branches. It is the gift of seeing some sort of order behind cirucmstances in which almost all the details are accidental.
Math synthesizes complexity; in biology, you have to analyze what's given.