Speaking of talk radio (which I was last month), Mike McConnell, the best talk show host currently on the air anywhere in the country, has suggested that the single most important contributing factor in the "obesity epidemic" is the relatively recent introduction of air conditioning and heating. This makes a huge amount of sense, given the fact that most of the time we're inside we are sitting on our asses and that air conditioning encourages us to stay inside. Heating used to be accomplished in a more manual fashion, predicated on hauling something inside to burn. People in more northerly climates enjoy a more friendly outdoor experience in the summer, and those of us cursed with a Texas address in the summer get compensated with comparatively mild winters. But the net effect of air conditioning technology is an increased average amount of time spent indoors sitting on our asses.
This leads to problems, because we have not spent the last 65 million or so years finely honing our physiology to watch Oprah. Like it or not, we are the product of a very long process of adaptation to a harsh physical existence, and the past couple centuries of comparative ease and plenty are not enough time to change our genome. We humans are at our best when our existence mirrors, or at least simulates, the one we are still genetically adapted to live. And that is the purpose of exercise. But the problems that are created by ignoring this are not just physical. Diabetes, obesity, osteoporosis, heart disease, hypertension, sarcopenia, and bad breath are only a part of what's wrong with the way the twenty-first century treats its precious children.