Across the United States and Mexico, Essay Example

Across the United States and Mexico range the common house finches (Carpodacus mexicanus).  These birds are sometimes called Mexican House Finches.  They are a medium sized finch, averaging 13-14 cm (5-6 in) in length.  Their diet consists mainly of forage, small seeds, fruit, and sometimes insects.  Their beaks are small and stout, making them perfect for crunching seeds. These birds are permanent residents and do not migrate.

A small population of Mexican house finches becomes isolated on a small island off the gulf coast of Mexico after a storm.  High winds carry a number of individuals some miles off shore into the gulf onto a flat coral island.  The vegetation on this island is scarce.  The finches beaks are adapted to crunching seeds, however, the birds find that since vegetation and seeds are scarce, they much hunt for another food source.

In this population, there are some members who have slightly thinner and longer breaks.  These members find that they can hunt small invertebrates that live in the sand and in between and under rocks.  The members who hunt more successfully live longer and lay more eggs.  Since they are the more successful members of the population, their genes, the genes for longer, thinner beaks, are passed onto the next generation.

Over time, the island population of Mexican finches begins to take on a distinctive characteristic of having thinner and longer beaks than other member of Mexican finches living elsewhere in the world.  The random genetic mutation that occurred in some members of the original population allowed those members to be more successful hunters and breeders and thus became, over generations, the dominant characteristic instead of a recessive trait.