Darwins Finches

A historical example of Natural Selection...

Introduction

The Galapagos Islands are an archipelago of 13 major islands and more than a hundred smaller islands that are situated off the Ecuadorian coast. They are home to an array of unique animal species: giant tortoises, iguanas, fur seals, sea lions, sharks, rays, and 26 species of native birds - 14 of which make up the group known as Darwin’s finches.


These finches are considered to be the world’s fastest-evolving vertebrates because their appearance and behavior quickly adapted to this closed and rapidly changing environment.

Because the Galapagos are a set of islands:


  • Terrestrial species on these islands won’t have many relatives nearby.
  • Neighbouring islands will have close relatives
  • New terrestrial species won’t arrive on these islands from the South American mainland very often.
  • Most of the island species have had abundant time to differentiate from their nearest living relatives.

All these factors combine to illustrate that there is very limited gene flow between the islands and the mainland, encouraging divergent evolution in the process of Natural Selection.


So what is natural Selection? Watch the Video below...

What is Natural Selection?

Darwins Observations:

Darwin noticed that the finches on the different islands there were fundamentally similar to each other, but showed wide variations in their size, beaks and claws from island to island. Darwin came to understand that any population consists of individuals that are all slightly different from one another. Those individuals having a variation that gives them an advantage in staying alive long enough to successfully reproduce are the ones that pass on their traits more frequently to the next generation. Subsequently, their traits become more common and the population evolves. Darwin called this "descent with modification."


The Galápagos finches provide an excellent example of this process. Among the birds that ended up in arid environments, the ones with beaks better suited for eating cactus got more food. As a result, they were in better condition to mate. Much the same, those with beak shapes that were better suited to getting nectar from flowers or eating hard seeds in other environments were at an advantage there. IIlustrating the process that came to be known as Natural Selection.




The diagram below illusrates how environmental changes influence some Finch populations.

Adaptive Radiation

Darwin's finches are an excellent example of the way in which species' gene pools have adapted in order for long term survival via their offspring. The Darwin's Finches diagram below illustrates the way the finch has adapted to take advantage of feeding in different ecological niche's.
Their beaks have evolved over time to be best suited to their function. For example, the finches who eat grubs have a thin extended beak to poke into holes in the ground and extract the grubs. Finches who eat buds and fruit would be less successful at doing this, while their claw like beaks can grind down their food and thus give them a selective advantage in circumstances where buds are the only real food source for finches.

Today we use the term adaptive radiation to refer to this sort of branching evolution in which different populations of a species become reproductively isolated from each other by adapting to different ecological niches and eventually become separate species, just as the Finches have.


The adaptation has led to a large variety of Finches..

Galapagos: the finches (4/7)

Conclusion

The Galápagos finches serve as a fascinating example of natural selection in action, by evolving according to the food available to them, the Finches illlustrate the Theory of Natural Selection. As Darwin himself said...

'It is not the strongest of the species that survive, nor the most intelligent, but the one most responsive to change'