[dividedbyzero]

There was Homo floresiensis, a relatively close relative of ours, also called the "Hobbit". For modern humans, there simply are no known populations that have been isolated for long enough on a small enough island to exhibit dwarfism. We're pretty good with boats and we supposedly have been very mobile for most of our history, and even if stuck we're capable of controlling our numbers and exploit our environments very well. I believe there are adaptations among Pacific Islander communities that increase metabolism efficiency and similar traits so we're not immune to this kind of pressure.