Evolution ?

They came from the seas.

They crawled slowly, gasping for breath in the unfamiliar atmosphere, lungs compressed by bodies designed to be supported by water, unfamiliar with the full effects of gravity.

And they died.

Generation upon generation, they died, but they kept on coming. Some made it farther than the others. Those with stronger ribcages, larger muscles, more capacious lungs were able to return to the sea again.

And they bred.

Slowly, generation by generation, over the millenia, their sojourns onto land became longer, more determined, more intrusive. Bodies designed for life in the water mutated, changed, adapted to the new environment. Limbs twisted, became able to bear weight. Lungs took oxygen from the air. Muscles lengthened, strengthened, changed focus.

And they bred.

Until the day came when the need to return to the waters was no longer there. They were no longer dependent on the sea to live, they could roam the lands at will, albeit slowly, sedately with their unfamiliar and ungainly bodies.

And they encountered others. Others that had made the journey from sea to land, who had adapted more readily and developed more quickly. They observed the small communities from afar, watching the interactions, listening to the sounds, the vocalisations of these strange beings...

"Hey, Chuck, there's another one. Quick, shoot it. Get the gun! Don't let it get away, there's good eating on those big ones."