Finches beaks and overall head shape adapted to live in certain areas or eat certain foods. These adaptations are due to natural selection, as the birds with the best suited beak for certain foods (an example) are most likely to survive than those that cannot.
The finches adapted over time to better suit their environment that they were in -- the size and shape of their beaks changed as a result of natural selection.
Humans are warm blooded and can't be cold blooded because of the environment we live in. We can't sit still during the winter and soak up warmth from the sun.
