Why is it that only that oiler dies and not anyone else in Crane's "The Open Boat"?

In Crane's short story "The Open Boat," four men are lost at sea in a small boat. At first it seems that none of them will survive, but as the story goes on, the men spy land and have hope that they can make it ashore. Because the captain is injured, the other men must take turns rowing the boat. Since they have virtually no supplies, this physical exertion is exhausting. The oiler is the strongest man--physically--on the boat, so much of the rowing falls to him. Therefore, as he continues to row, the other three men are able to take short rests and conserve their strength.

This becomes important when they decide to make a break for it and swim to shore. The oiler, who is completely depleted of energy because he has been rowing for most of the time, does not have the strength to swim to shore and dies. This story ironically reverses the notion of Darwin's survival of the fittest: while the oiler seemed to be the fittest and strongest of the four men, he used up his energy, which made him the weakest and the mostly likely to die.