The Island Syndrome
Remarkable species often evolve on islands, a phenomenon known as "the island syndrome".
The mild climate of an island can explain why humans did not need fur for warmth or sun protection. The lack of large predators on an island can explain why humans could evolve slow and awkward bipedal walking and lose muscle strength. (An average chimpanzee is considerably stronger and can run much faster than any human in the Olympics.)
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Island syndromeFrom Wikipedia, the free encyclopedia
Island syndrome describes the differences in morphology, ecology, physiology and behaviour of insular species compared to their continental counterparts. These differences evolve due to the different ecological pressures affecting insular species including a paucity of large predators and herbivores as well as a consistently mild climate.
Ecological driving factors
Island ecosystems cannot support a sufficient biomass of prey in order to accommodate large predators. This largely relieves prey species of the risk of predation, which mostly removes the selection pressure for morphologies, ecologies and behaviours that help to evade large predators. Insular ecosystems tend to comprise large populations of a limited number of species (a state termed density compensation), therefore, they exhibit low biodiversity. This results in reduced interspecific competition and increased intraspecific competition. There is also reduced sexual selection in insular species, which is especially prominent in birds which lose their sexually dimorphic plumage used in sexual displays. Finally, there is reduced parasite diversity in insular ecosystems which reduces the level of selection acting on immune-related genes.