ScienceDaily — In the evolutionary long run, small critters tend to evolve into bigger beasts -- at least according to the idea attributed to paleontologist Edward Cope, now known as Cope's Rule.
As for why Cope's Rule works at all, that is not very well understood, says Gene Hunt, curator in the Department of Paleobiology at the National Museum of Natural History (NMNH) in Washington, D.C. "It does happen sometimes, but not always," he added. The traditional idea that somehow "bigger is better" because a bigger animal is less likely to be preyed upon is naïve, Hunt says. After all, even the biggest animals start out small enough to be preyed upon and spend a long, vulnerable, time getting gigantic.
from sciencedaily