Examples of cause and effect in the story A Sound of Thunder?

Answer 1

Cause: When Eckels stepped off the path, he inadvertently stepped on and killed a butterfly.

Effect: When Eckels and the others returned to the future, they found that people were "stupid" (examples: the spelling on the sign was incorrect; the people voted for the dictator rather than the "good guy" for President).

Why: By killing the butterfly, Eckels made every descendant of that butterfly cease to exist. Animals that might have benefited from those butterflies, perhaps by eating them, or eating animals that ate butterflies, would not be able to do so. Some animals may have gone extinct altogether; some may have been undernourished or underdeveloped as a result. The "butterfly effect" eventually traveled up the food chain to human beings. Because the food chain was altered, human beings developed differently, seemingly less well than they had in the original time line, and because of those developmental differences, the humans in the future made some different choices than what they would have done had Eckels not stepped on the butterfly. Because of the time travel paradox, Eckels (or one of the others) could not go back in time to stop Eckels from stepping off the path, so he had to pay for the damage he had done, with his life.