Evolutionary reason for naturally skinny people?

What is the evolutionary reason why there are naturally skiny and tall people like myself like its just seems like if it were the caveman days people like me would not survive when all the naturally muscled or naturally fat people are there like who seem...

to have better chances of survival then tall lanky kids...

There doesn't need to be a clear evolutionary advantage: There's room for a lot of variation in populations without affecting survival chances much either way. If being taller, or shorter transpires to be better for survival, the average height of the population will gradually migrate in that direction.

well...actually they needed us to pick on the tall fruits that grow on tall trees...so we have an evolutionary advantage...I mean they would have died if they only lived on meat diet but thanks to us we supplemented them with the various fruits that grew on trees...it's complementary oh also when dinosaurs come after our a*ss we can play being a twig or bark and they'd just run right through and eat the meaty people(:-D

not sure, it may have had something to do with climate though. Taller, leaner people would probably cope better with a warmer climate. I dont think there is any evolutionary advantage now though, we dont really do anything ourselves now, just really on technology etc. The majority of people havent evolved from when humans had a hunter gatherer type lifestyle, hence why obesity is such a problem. We're designed to retain body fat because we dont know when our next meal will be, only in our society we dont have the same problems in finding food and our bodies cant deal with that.