If we had no weaning rules and guidelines, how would we do it, instinctively?

[AndOutComeTheBoobs]

No books, no internet, no mother in law giving you tips.

Just a baby and parents. How does weaning occur naturally?

Is it when the baby starts to put things in their mouth (but this happens every young - 3 months?) is it when they start to crawl and grab at things (this can be much later, if at all if you're my second son).
Is it when the baby reaches out for the parents food?

How would a parent wean a baby before all science and knowledge?

I read years ago that we kissed a little food into our baby's mouth while we ate. Not an organised attempt at weaning, so much as sharing a little of what we have when we have it.
As the baby grows, it will be more determined to raid mum's mouth. That feels very natural to me.