That's exactly why there is still argument about the effect of power lines on people. You'd have to keep track of a LOT of people to be sure that a difference is real, and not just chance. You also have to be sure the flies ate the same food, got the same lighting, and so on. With people you have to compensate for diet, smoking, workplace related disease, etc. Ultimately, science is done by people in a real and challenging environment.
Mistakes happen, even to people with the best training and intentions.
All rights reserved.