Nature has been adapting to different climates for billions of years. It's difficult to visualize the progression unless you map out each phase of the process. It's hard to understand that the smallest change, like in the length of a bird's beak, could affect the success of that species. Hoefler & Frere-Jones took this idea and applied it to type. Depending on the climate, the smallest change in the stroke weight will either increase or deceases the readability of the type. A type that adapts well to its environment.