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The Island Rule: Why Humans and Animals on Islands Tend to 'Shrink'

Dec 15, 2016 10:29 AM EST
Small donkey
The Island Rule: Smaller islands require smaller organisms.
(Photo : Spencer Platt/Getty Images)

The Island Rule is one of the best explanations scientists could give to the observable phenomenon that animals and humans have evolved depending on the resources available in their habitat. Through time, scientists have noticed through fossil records that some large animals from mainland habitats have dwarf versions in island habitats.

A report from BBC described the existence of what scientists call "hobbit island" off a small island somewhere in Indonesia. It was given such a name because fossil records of tiny, human-like creatures have been found in the region. What they called as "hobbits," or Homo Floresiensis, are only as tall as one meter and are small versions of early human species with tinier brains.

Though scientists cannot perfectly trace the origin of the Homo Floriensis, they believe that they are human relatives, but it is the "island life" that has caused them to evolve as they have. Scientists have noticed through fossil records and existing organisms today that it seems as if large animals grow small in islands while small animals grow large in larger islands.  

What is known as Insular Dwarfism, it would seem that in theory, animal and human bodies have adjusted to the very little available food and fresh water in their habitat. Since there is no opportunity for them to live their island, they might as well adapt.

New York Magazine explained that islands usually have lesser predators than mainland ecosystems. However, it is the lack of resources that cause the death of many animals. As a means of natural adaptation, the bodies of these animals have evolved smaller than their ancestors, making their bodies require fewer resources.

A report from Web Ecoist listed down a few examples of insular animals that have shrunk significantly compared with their ancestors. Some of these include the pygmy hippo the size of pigs from Liberia, the endangered dwarf water buffalo from the Philippines, and the Bali tiger as small as leopards.  

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