SittingComfortably asks: "lets say I have Baby1, and get pregnant again when Baby1 is 7 months old, do I breastfeed Baby1 up until Baby2 is born and then breastfeed BOTH until Baby1 is 4 years old?"
Yes. It's the law. Didn't you know?
" What happens if I am pregant with Baby3 before Baby 1 is 4 years old? Do I breastfeed ALL 3? "
Absolutely. Again this is the law.
Jee-zus.
"If I don't then am I depriving Baby1 of what nature intended him to have, or did nature actually intend us to pop babies out much more frequently than we do? How then can nature intend us to bfeed up to 4 years old?"
Nature is probably most closely read in pre-industrial societies, because we see more clearly how evolution has developed the body and its functioning.
Nature does not intend us to have lots of children particularly - breastfeeding suppresses fertilty, and if you bf frequently and for a long (in western terms) time, you will probably not have three children in under four years (though in a lifetime you will have more than the one, two or three Western average). In pre-industrial societies, long-term bf is convenient, an important source of nutrition, and a useful means of spacing babies. The same can apply here, but we also have alternatives which we can choose to use instead.
Plenty of us do not live our lives according to pre-industrial social and biological norms, though, and that's ok, too