Evolution by natural selection.

Thousands of sea turtle eggs are laid each season, but less than 10% survive to adulthood, and fewer will find a mate and reproduce.

Darwin observed that many organisms produce more offspring than can survive to reproduce.

He proposed natural selection as the process that allows a few individuals with "favorable variations" to survive and reproduce - and pass on those "variations" to offspring.

Over time, accumulation of favorable traits results in adaptation of organisms to their environment.

The long-term result is evolution of new species: an ancestral common ancestor may yield offspring that evolve into separate species.