Do you think the ability to store fat, is an evolution for humans?

I understand that some people with high metabolism feel the need to eat all the time. Understandably, they are in fact needing as much energy as they can because due to higher energy outputs within their body. Now, for some reason I believe the ability to store fat, is adaptive and beneficial evolution from an Anthropology stand point, because in the past, when we were hunting, animal fat was hard to come across. And fat is needed for our brain to function well, it’s technically the same substance needed to create the brain tissue. Anyways, I have friends who are really skinny, but can’t run as long as my friends who tend to weigh more, and I think if you put a fat guy and skinny guy on an island that were chained up, the fat guy would live longer. Does that statement validate my thinking that storing fat is an ability and beneficial evolution?