|I've used this pic before. I don't care.|
What Findlay did, essentially, was induce rickets in dogs by keeping them sedentary. He would keep them locked up indoors in cages, providing them food of course, until they would develop symptoms of rickets. Then, as an experimental treatment, he would take some of the dogs outside and let them run around. Allowing the dogs to run around outside cured their rickets, and so Findlay assumed that exercise was the reason why.
Today we know that rickets is caused by a lack of vitamin D. As you may know, we can get vitamin D from simple sun exposure. It wasn't the exercise that cured Findlay's dogs; it was the sun. But put yourself in Findlay's shoes for a moment... if you didn't know that we could make vitamin D from the sun, how would you ever even identify that as a factor in your experiment? You wouldn't... because we just don't know what we don't know. Based on what we knew at that time, his experiment was air tight.
In hindsight, the idea that exercise cures rickets is absurd. But think about it in the context of the future... we'll likely be saying the same thing 100 years from now about what we believe to be true today. In any experiment, the goal is to control for the desired variable as best we can, so that we can be sure the results are due to that one variable and no other. We try to do this, or course. But in reality, there's no way to know what we don't know, and we can't control for that.
Take an example. Say we're testing the effectiveness of a gluten-free diet on symptoms of irritable bowel syndrome (IBS). So we recruit people with IBS, put half of them on a gluten-free diet, and keep the other half on their normal diet. We make sure both eat the same amount of calories, carbs, fat, and protein. The only difference appears to be the presence of gluten, but is it really? What don't we know? Well, for starters, we don't know much at all about the gut. I'm talking about the microorganisms that live there, what their roles are in our health, and how food might impact it. We also can't quantify the impact of stress... what if it's extremely stressful for someone to give up gluten? How does that impact things? We know very little of the compounds in food... take a carrot for example. We know of dozens and dozens of compounds within a carrot, and there are likely dozens more that are unidentified. On top of that, we really only know the biological function of a select few of them! What else don't we know? We just don't know! As you can see, nothing can be 100% controlled for, and nothing is really known for sure.
What will we know in 100 years? Maybe it'll be common knowledge that air conditioning gives us cancer!! Doubt it, but who knows!?
My point is this: we should always keep an open mind. We should always remember to stay humble and understand that we don't know it all. There's no telling how things could change in the future!
On another note though, there are certain things we CAN take to the bank... like eating whole foods. Doing what humans have always done, and have been successful doing, is always a safe bet!