Nature’s Laboratories

Two tortoises on the Galápagos Islands. (Source: Magnum Photos)

Natural selection is a slow process, its adaptations refined over millions of years, but there are some places on Earth where evolution kicks into overdrive. Islands have been called nature’s laboratories, their geographical isolation spawning off unique menageries of life unlike anything on the mainland. It was his time on the Galápagos Islands that informed Charles Darwin’s theory of evolution, based in part on his observations of closely related species of birds having different attributes best suited to their specific island. Each island in the Galápagos Archipelago functioned as a test case for Darwin, much like a laboratory experiment.

In the Galápagos case, the divergence of life owes itself to adaptive radiation, wherein different species spawn off from a common ancestor that then fill an ecological niche. It remains a debate which factor is the prime driver of change. Does the proliferation of a species cause its members to fill ecological niches, or do the niches themselves prompt the speciation? On the Galápagos, the latter seems to be the case, as there is far less speciation on the comparable but more isolated Coco Islands to the north. A high number of animals alone do not prompt evolutionary change, there still needs to be different niches for the animals to fill.

A pygmy mammoth being excavated. (Source: NPS)

Our understanding of how life adapts to isolated environments has greatly advanced since Darwin’s day, such as with The Theory of Island Biogeography. Published in 1967, the book outlined a model where island’s ecosystems are in a perpetual equilibrium, balanced out by extinction of existing species replaced by new immigrant species. More contemporary studies have expanded the picture even more, where islands are better understood not simply as closed systems but themselves constantly adapting to sea level changes and tectonic forces that effect a given island’s habitat. 

Islands as laboratories may not be a completely solid metaphor—they themselves are as changing as the species they harbor, but their habitats are still unique in the animal kingdom. These land masses are known to prompt considerable size changes in different species, wherein smaller species grow larger and larger species shrink, like the pygmy mammoth of the Channel Islands. Our understanding of how exactly islands shape life is also always in flux, but they still provide valuable insight into these evolutionary forces.