The answer is found in various religious traditions, especially Christianity. "Far from denying life's progression, tradition provides a reason for it," wrote Huston Smith in 1976. "Earth mirrors heaven. But mirrors, as we have noted, invert. The consequence here is that that which is first in the ontological order appears last in the temporal order." Smith explained: "In the celestial realm the species are never absent; their essential forms or archetypes reside there from an endless beginning. As earth ripens to receive them, each in its turn drops to the terrestrial plane." But "first a viable habitat must be devised, hence the inorganic universe is matured to a point where life can be sustained. And when living beings do arrive, they do so in a vaguely ascending order that passes from relatively undifferentiated organisms... to ones that are more complex." Thus "man, who is first in the order of worth on the terrestrial plane, will be last in the order of his appearance."2