Populations of a shrimp species at eleven different Indonesian coral reefs show substantial genetic differences from one reef to another. This is surprising because the area' s strong ocean currents probably carry baby shrimp between the different reefs, which would allow the populations to interbreed and become genetically indistinguishable. Which one of the following, if true, most helps to explain the substantial genetic differences among the shrimp populations? ['The genetic differences between the shrimp populations are much less significant than those between shrimp and any other marine species.', 'The individual shrimp within a given population at any given Indonesian coral reef differ from one another genetically, even though there is widespread interbreeding within any such population.', 'Most shrimp hatched at a given Indonesian coral reef are no longer present at that coral reef upon becoming old enough to breed.', 'Before breeding, shrimp of the species examined migrate back to the coral reef at which they were hatched.']