Elephants use their ears to cool themselves down with the high temperature weather they live in
Mutations can cause variation of traits within a species. In this case, some elephants are born with short ears and some are born with long ears. The brown elephants are the long eared and the grey are the short eared.
Overproduction produce more young than the environment can support which leads to competition for food and danger of predators . This example is showing the short and long eared elephants. The short eared elephants aren't capable of cooling themselves down because their ears are too short to reach and fan themseleves down.
Organisms whose variation trait are best adapted to their environment tend to have a longer life because they are fit. So the long eared elephants are best suited for this environment because they can cool themselves down.
Them not being suitable to live in there environment would change their gene pool. Over several generations, the best variant trait are the ones left.
In conclusion, this leads to the next generations being more long eared elephants because the short eared elephants can't live in their environment and die because of the heat