In the sort term, new traits among individuals (or sub-groups of the species) come about through 'mutation'. But long-term change comes about through the greater survival of those individuals (or sub-groups), i.e.
'evolution' [which appears to be the answer you're seeking].
Chris
PS: New members posting at this time of day/night are often in the USA. This is a UK-based site; while we welcome questions from all over the world, there aren't many people around to answer at 3.20am, when you posted. If you're in the USA and seeking answers around this time you might get quicker responses on US Q&A sites such as
http://answers.yahoo.com/
or
http://www.answerbag.com/