DNA: I find DNA and genetics very interesting. They combine the personality traits and the appearance to make someone similar to both but not exactly. DNA is not perfect. Every time someone is born mutations happen. Lets take the example of bears. At first there where just bears. Then (eventually) a major mutation happened. At the time that bears were being more driven towards he colder part of the earth a bear got born with a little more resistance against cold. He/she mated with another bear and got children.
Then Their child mated with another bear and the mother mated with a different one then the first. Eventually there were lots of bears with just a little bit more cold resistance. When two bears with a little more cold resistance mated then they got one bear with more cold resistance then at first. That went on for a long time until you got the first polar bear.
Link to my moms bog: http://isabelagranic.com/