Keep Out by Fredric Brown — Read

_With no more room left on Earth, and with Mars hanging up there empty of life, somebody hit on the plan of starting a colony on the Red Planet. It meant changing the habits and physical structure of the immigrants, but that worked out fine. In fact, every possible factor was covered -- except one of the flaws of human nature._

Daptine is the secret of it. Adaptine, they called it first; then it got shortened to daptine. It let us adapt.