I find this subject amusing, this has been going on for ever, on this planet and others it has and will never stop, it is not possible to stay with ones race because at a certain point in history, inbreeding will occur, this is a constant and a cosmic rule. You cannot stay with your own people forever, the same way the earth cannot stay the same.
It has been attempted by numerous races across existence, and its always ended up in failure. Im pretty sure you are aware of reports of aliens abducting humans and doing experiments on them right? For example the greys, they essentially screwed up their genetics This is the end result of a race trying to stay " pure " http://www.thinkaboutit-aliens.com/w...10/serpo03.jpg