>Even the childless often have nephews and nieces to leave something to. Even those with no one they want to leave anything to may have causes they want to further.

Yes, but I wonder if there is the same sense of responsibility to do so that a parent would feel. It is also possible that without children, the inheritance from an uncle/aunt for example would be far more, since there is still the human drive to collect in play. But, I think that the culture of what to collect is changing, where perhaps not as much of it holds value over time - like experience and skill, which largely dies with us.