Responsibility is always socially constructed. The idea that one person can “owe” another doesn’t exist without people. It’s not a law of nature.
That said, we have drifted very far from the nasty, brutish, and short version of prehistoric society, where your parents might be some of the main people you ever interacted with. Taking care of your parents in that context is quite obvious, because when you were helpless they took care of you, and otherwise no one will take care of them.
> Taking care of your parents in that context is quite obvious, because when you were helpless they took care of you
Well, let's be clear, that is far from universally true.
There's also degrees of care.
I absolutely see where the GP is coming from: my parents chose to have me, I didn't choose to have them. So why would I owe them for simply living up to the responsibilities they chose to take on?
Now, for amazing, supportive parents, the child will want to support and care for their parents when the time comes.
But not everyone has good parents, and I do not believe a child has a responsibility to care for an absent, abusive, or otherwise bad parent simply by dint of genetics.
That said, we have drifted very far from the nasty, brutish, and short version of prehistoric society, where your parents might be some of the main people you ever interacted with. Taking care of your parents in that context is quite obvious, because when you were helpless they took care of you, and otherwise no one will take care of them.