Twins.

If two identical twins were separated at birth, one going to a rich family and the other to a poor family I think the difference in the twins would be severe. The twin that went with the rich family would probably have a totally different out look on life then the poor twin. The richer twin probably wouldn't know what it was like to have to forge for food and wouldn't know how or what it was like to work hard and earn little. So personality wise I believe that the twin brought up in a poor family would have a better grasp on what it's like to value and respect things. The richer twin would only know that if something goes wrong or breaks, that he can always buy or get a new one. Appearance wise I think the rich kid would be fat. Well maybe not fat but he would never have to worry about a meal. The poor twin would probably be scrawny. Either that or the poor twin would be more muscular seeing as though he would have to work hard to get what he wants and needs.