Why do some chooks have more fat than others?

[bwmichaud]

I just slaughtered 2 Buff Orpingtons yesterday and one was noticeably heavier than the other. Once I opened them up, I noticed one (The heavier one) had huge fat deposits in the abdomen and the other had none to speak of. They have been raised together and fed the same stuff. I let them run loose and forage for whatever they like. Do you think that the fattier one just found more bugs and frogs and stuff?

 

[emys]

Genetics is my guess. (If hens probably wasn't laying as well, putting energy into fat rather than eggs.)