Comics know physics

Answer: This is the DC Comics version of the physicist's famous "grandfather paradox," says James Kakalios in "The Physics of Superheroes." If you could indeed travel back in time, it would be possible to murder your grandfather when he was young, before your own father was conceived. In this way you would prevent your own birth, but the only way you could have prevented it is if you had first been born!

Having stumbled on the paradox, Superman sets out to defy it. Going back in time proves no problem; he just travels fast enough to break the "time barrier." Once in the past, he does seem able to change the course of history, but when he returns to his present in 1961, he finds the history books unchanged: Lincoln was indeed shot at Ford's Theater, etc. What happened?

Question: Our long legs with long spring-like tendons, compact feet with longitudinal arches, small toes, shock-absorbing knees, big bottoms (larger than other primates), long waists, broad shoulders for stability, copious sweat glands, minimal body hair, tendency to breathe through our mouths during strenuous activity. . . . What's the point?

Answer: All are ideal human adaptations for running, suggesting to anthropologists that running and especially endurance running (also unique among primates) has been far more important in our development as a species even than walking, says archaeologist Steven Mithen in "The Singing Neanderthals: The Origins of Music, Language, Mind and Body." We humans are happy runners, and runners it seems we long have been.

Question: You're dreaming — or at least you think you are. Is pinching yourself a good reality check?