Interesting Q, Beatrice....we can get some idea of what bf is like physiologically by looking at other societies where it really isn't problematic. These tend to be pre-industrial societies, where women expect to breastfeed and where no one expects mothers and babies to be separated at all, from birth onwards. Girls grow up seeing babies being breastfed often - no one bothers counting how many feeds or looks at the clock to time the length of the feed....babies may feed many scores of times in 24 hours.
In these societies, babies do just fine, on the whole, though when they get to toddler age, they tend to grow less well than they should if food is scarce for the family.
It's not just the developing world, though. In Scandinavia, for instance, mothers tend not to bf dozens of times a day, but because the understanding of how to bf is something girls grow up with, there is less of a technique to learn. Something like 98 per cent of babies begin bf and the vast majority of them continue excl or predominantly bf for at least the first several months (the exact figures not to hand, sorry).
Not having enough milk, or sore or cracked nipples, are not unknown problems in these places - but there is more skill available in ovecoming them.
When the conditions are right, most women can breastfeed, but it seems one of the most important conditions is having a society where bf is overwhelmingly the social norn. That way, you grow up knowing what it looks like, and so positioning is less of a challenge; the skills to support bf are also part of every woman's folk knowledge.
There is a lot more about all of this in the book The Politics of Breastfeeding by Gabrielle Palmer.