Nature doesnt intend - it evolves. There is no design. Nature has left us with a useless appendix, skeletal issues from walking upright, a nerve that traverses all the way up and down a giraffes neck needlessly, and a variety of other 'dud' left overs.
Culture plays an important part in behaviour. Do you think nature 'intended' us to wear clothes, eat with a knife and fork, drive cars, sit at comouter desks? Of course not - but as a species we evolve to accomodate these things.
Many human societies have chosen different methods of child rearing than the modern western standard of a 'family unit' - to suggest that the modern western standard is the only correct way is simply historical/cultural arrogance.