Evolution in Beak Size

Evolution generally happens over hundreds of years and is usually not noticeable in one’s lifetime. The evolution of beak shape in Galapagos finches is an exception to this. The Galapagos finches have a variety beak shapes. They range from long and skinny to deep and thick. Their beaks are adapted to the type of seed they eat. The small beaked finches feed off small fleshy seeds. The thick beaked finches feed off tough thick seeds. The range of beak morphologies directly reflects the foods they eat. The sizes of these beaks are generally pretty even. During years of extensive drought a shift in beak size can be seen. The drought has to occur over a few generations for the results to be seen. The thick beaked finches can eat tough seeds that are resistant to drought. These birds are unaffected by drought. The thin beaked finches often struggle during the drought years. Their small fleshy seeds become very sparse. Their beaks don’t allow them to eat the tough seeds and the birds often die as a result of starvation. Their death means that they cannot pass on their thin beaked genes. The thick beaked finches are healthy and can reproduce. Their thick beaked genes are passed along, creating a shift. The shift is towards thicker beaks. The thick beaked finches are able to continue to pass along their genes while the thin beaked finches continue to struggle. There are finches with intermediate beak size and are also able to pass along their genes. Over a few generations you are able to see a shift toward thicker beaked finches.

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http://www.pbs.org/wgbh/evolution/library/01/6/l_016_01.html