"It's only natural," I said. "When we were kids, Bud, we saw the same TV programs, the same space-adventure movies, as the kids who are now the men in space. Every boy in America was conditioned to long for a space-suit. I'm one of the ones who could have made it, Bud. I love medicine, and I think I'm going to be a damned fine pathologist; but I'd turn in my M.D. for an Ordinary Spaceman's ticket without a second's hesitation. When I read, two years ago, that Immermann had discovered that human skull in the oxide rubble below Roosevelt Ridge in Syrtis Major, I cried for the first time since I was six years old. Twenty thousand years ago there was man on Mars. And I'm confined to Earth for life." "How much do you know about the Immermann skull, John?" Dorsey asked me. "What I've said. Is there more?" "One point," Dorsey said. "My field, radio astronomy, is a deep-space sort of specialty; but I do from time to time condescend to read the _Journal of Aerology_ and the other parochial, solar-system publications. Somewhere I read that there's something odd about that skull Colonel Immermann dug up." "If you're suggesting that it was a second Piltdown hoax, planted in that Martian talus to jar larger Air Force appropriations from Congress, keep it from me," I said. "I cherish the illusion that the Immermann is genuine, and a mystery." * * * * * "It isn't phony, and it's sure as hell a mystery," Dorsey said. "Colonel Immermann's initial report of the skull's discovery was verified by every member of the _Orion Gamma's_ crew, a gang recruited mostly from Service-Academy grads and other high moral types. The peculiarity I'm talking about isn't forensic. It's functional. If you were to mix in the Immermann skull with an assortment of skulls of modern western men, age forty or thereabouts, only one characteristic would allow you to pick it out from the mixture again. 'Look, Mom--No Cavities!' Like us Lapins, Immermann Man had acarious teeth." "Because he was germ-free?" I suggested. "It's possible. Or his medical science may have gotten oral bacteria under control with drugs. Maybe he preserved his teeth by diet, or with fluorides in his drinking-water. Perhaps his mother never let him eat candy when he was a kid," Dorsey said. "Who knows? Good teeth and all, though, our Immermann Man died twenty thousand years ago. Why? Was he germ-free, as you suggest; and was he killed by some species of Martian micro-organism that's since gone extinct from drought and a shortage of hosts? The big question, to my mind, is why none of our explorers has yet found any sign of the rest of the expedition." "Expedition?" I asked. "A man could hardly have been alone on Mars," Dorsey said. "From where?" "Pick any 'F'- or 'G'-type star with planets," Dorsey said. "After all, it's easier to posit extra-solar man than to suppose a flint-drive spaceship was devised by some early neolithic von Brauns."