There are two sorts of islands. One sort provides powerful evidence of evolution at a species level.
Firstly there are continental islands. These were once part of larger land masses but they were cut off by rising water levels or the movement of tectonic plates. Great Britain is an example of a continental island, it was cut off from the rest of Europe 300,000 years ago. Continental islands have a large and balanced population of flora and fauna.
The other sort - the one we are interested in - are oceanic islands. These rise brand new from the ocean due to the effects of volcanoes or the growth of coral reefs. Examples of this sort of island include Hawaii and the Galapagos Islands. Logically these sort of islands have no life at all when they first appear but they end up with an unusual collection of species.
They get colonised accidently by species that are able to reach them. They lack things like fresh water fish and land mammals and with a few exceptions, reptiles and amphibians.
The species that do make it to an oceanic island tend to prosper outrageously. With little or no competition the original coloniser ends up being the ancestor of a whole range of species that have adapted to fill the variety of available niches on the island or archipelago. This phenomena is known as "adaptive radiation". Frequently these species are endemic to the oceanic island - in other words they are not found elsewhere.
For example in the Galapagos Islands there are 28 endemic species of birds. Fourteen of these are closely related and make up the famous Galapagos finches group. Similarly Hawaii had 140 species of native bird. Sixty of these were honeycreepers that had all descended from a single pair that arrived there 4 million years ago. Although these species are similar there is no doubt that they separate species by any definition of the word.
Similar radiations are found among plants and insects on oceanic islands.
The really interesting thing about the animals and plants that inhabit oceanic islands is how remarkably similar they are to species found on the nearest mainland. Life on the Galapagos closely resembles life in the west coast of South America. The same is true about Juan Fernandez where the closest relatives of species there can be found in the forests of South America. The same pattern is repeated again and again all over the globe.
These facts about biogeography is exactly what evolution would predict. It is down to chance which species make it to an oceanic island. Having arrived these Robinson Crusoe species thrive and evolve to fill many different ecological niches, and finally we will find their closest relatives on the nearest mainland.
|Part 1 - Protein Functional Redundancy - - - - - -||Part 2 - DNA Functional Redundancy|
|Part 3 - ERVs||Part 4 - Smelly Genes|
|Part 5 - Vitamin C||Part 6 - Human Chromosome 2|
|Part 7 - Human Egg Yolk Gene||Part 8 - Jumping Genes|
|Part 9 - Less Chewing More Thinking||Part 10 - Non-Coding DNA|
|Part 11 - Tiktaalik||Part 12 - Lenski's E.coli Experiment|
|Part 13 - Morris Minor Bonnets||Part 14 - Joey Goes to Oz|