Creating culture is unique to humans, it separates us from primates and other species, and through culture we are able to progress and create a sophisticated society, this is why some societies have different outcomes to others, because of differing cultures. A country will innovate more if its people have the culture to do so (risk taking behaviour), a country will be clean if its in people's culture detest a dirty environment etc , certain cultures have adopted different cultural values over the course of time and as a result, separate parts of the world have shown differing outcomes throughout the centuries.
Why can't this reasoning be extended to the family system?
A small example is how a Hindu believes giving prasad to attain enlightenment from his Gods will be beneficial for him, in his dimension he has lifted his ego, he may gain various chemicals in his brain from this interaction and due to this he performs better in other areas of life, even though the initial action was simply placing food under a statue, you can't explain this scientifically except for the chemical release in the brain part, it is more a cultural reason. And up until recently almost the entire world believed in some type of mythology/religion/spirituality which may have helped them in their lives one way or another, this is better "outcome" is explained through culture than biology. Nowadays you can do the opposite, you can use recent data to explain why religion is fading as a country becomes developed, but its still attributed more to culture, because adopting irreligious culture is more suited to getting ahead in the modern world.
I believe love works the same way, outcomes can be explained more through culture than biology. It is expected in our culture to care for our own child, we treat the child better for the cultural expectations, we abide with norms that shape our behaviour and relationships within the family system. On the contrary, one may be careless to treat someone else's child because its not expected in our culture to treat someone else's child to the same standard, hence the poorer outcome. Also these actions of conforming to societal norms may completely be subconscious rather than intentional, as humans have a remarkable ability to absorb and internalise the values and behaviours of their cultural environment without knowing it.
