The "island rule" in evolutionary biology posits that when mainland animals colonize islands, small species tend to evolve larger bodies (gigantism) while large species evolve smaller bodies (dwarfism) due to limited resources. Paleontologists recently discovered fossils of a dwarf elephant species on the island of Sicily. This finding supports the island rule by demonstrating that ______
Which choice most logically completes the text?
large mammals can undergo significant size reduction when isolated in resource-constrained environments.
islands typically support a greater biodiversity than mainland environments.
small mammals always evolve into giants when they reach islands.
elephants are the only species capable of adapting to island life.
Correct Answer: A
Choice A is the best answer. The text defines the island rule (large species evolve smaller bodies/dwarfism on islands). The discovery of a dwarf elephant (a large mammal that became small) on Sicily (an island) directly supports this part of the rule.
Choice B is incorrect because the text discusses body size evolution, not overall biodiversity. Choice C is incorrect because the fossil is a dwarf elephant, which illustrates the "large-to-small" trend, not the "small-to-giant" trend. Choice D is incorrect because the rule applies to "animals" generally, not just elephants.