Stephen Jay Gould has written that "historical science proceeds by reconstructing a set of contingent events, explaining in retrospect what could not have been predicted beforehand. If the evidence be sufficient, the explanation can be as rigorous and confident as anything done in the realm of experimental science. In any case, this is the way the world works....Contingency is rich and fascinating; it embodies an extensive tension between the power of individuals to modify history and the intelligible limits set by laws of nature. The details of individual and species' lives are not mere frills, without power to shape the large-scale course of events, but particulars that can alter entire futures, profoundly and forever"
The main goals in the evolutionary game are to eat, stay alive, and reproduce. The edge does not necessarily mean speed or strength. The idea of survival of the "fittest" means that someone has an edge in this game to eat, stay alive, and reproduce. Consider the story of a diminutive deer that gained a competitive edge. This deer lived during the Pleistocene some 125,000 years ago. At that time the climate warmed and icecaps melted. Sea levels rose globally as the climate changed. This cut off deer living on the island of Jersey in the English Channel off the coast of France. Only a very small isthmus joined the island to the mainland for much of the next 20,000 years. For about 6,000, Jersey was an island, isolated from the mainland. During this period from around 120,000 to 114,000 years ago, a group of small deer developed in this relatively isolated context. We know from studies of fossils that they were the only deer on the island. A period of 6,000 years is a relatively short period of time geologically, only about 2,000 generations of deer. Yet it was plenty of time to accumulate genetic changes to produce only small size deer. This was probably a change that happened gradually over generations but always directed toward smaller size. We will never know specifically why nature saw fit to have small deer on Jersey but perhaps it had to do with a restricted food supply and limited land on this isolated place. Small size would be a particular advantage during times of winter shortage, since island inhabitants cannot migrate to richer feeding groups, as can their mainland counterparts. We do know that large carnivores were absent on the island at this time. In the absence of predators, the deer populations would expand to the point where individuals must compete for food. This might mean small size was beneficial.
What is interesting, is that today there are no small deer on Jersey. They went extinct or at least disappeared from the fossil record. We do not know if these deer had become a separate species in the 6,000 years they were separated from mainland counterparts. If they had not reached this point of being separate species, then they may have been subsumed into the population of mainland red deer by interbreeding after the island was reconnected to the mainland. About 115,000 years ago as the climate once again cooled, sea levels were lowered. This led to a demise of the dwarf deer of Jersey.