Long necks were a random genetic change and resulted in the gradual increase of organisms with long necks.
Step-by-step explanation:
- According to Darwin, evolution occurred because natural selection allowed the organisms with higher reproductive and survival fitness to survive and eliminated the weaker organisms. As a result the population of the fittest organisms increases and their trait got established.
- According to Darwin, the giraffes with long necks and giraffes with short neck once survived together in an environment but gradually the natural selection eliminated the giraffes with short neck and favored the growth of giraffes with long necks. Hence, at a point of time the short necked population got extinct and long necked population thrived to establish itself.