Complex sentence: The explanation Harriman gives comes from an old urban legend that, based on weight ratios to wing power and wind resistance, the bumblebees should be aerodynamically incapable of flight--yet, the theory says, the bumblebee doesn't know that, so it flies anyway.
Split into simpler sentences: The explanation Harriman gives comes from an old urban legend that bumblebees are aerodynamically incapable of flying. Based on weight ratios to wing power and wind resistance, the bumblebee should be incapable of flight, yet, the theory says, the bumblebee doesn't know that, so it flies anyway.