All that "40 is the new 30" boosterism aside, midlife is not the start of a downward spiral. David Bainbridge is a clinical veterinary anatomist at Cambridge University, and the author of several books including Middle Age: A Natural History. He believes middle age might be a pivotal part of the human evolutionary process, and potentially the most productive years of our lives.
Does Middle Age Have an Evolutionary Upside?

(Photo by brondabailey via Flickr)