[Saline9515]

Primogeniture makes sense in a world where odds that you arrive at the adult age are rather low, due to the high risk of death from illness and injuries.

The oldest child is the most likely to survive. It is a rational and fair rule in such context.

[marxisttemp]

Many discriminatory policies could be considered rational. It is rational for jobs to discriminate against handicapped people who require extra affordances to be able to do the same job (for example, wheelchair ramps).

“Fair” is a much trickier beast! My favorite approach to conceptualizing fairness is Rawls’ veil of ignorance: if you were going to be placed as a random member of society, rather than your current position, and you would still support a policy given this change, then the policy is fair. Knowing that, beyond the veil of ignorance, I may be a paraplegic, would I still support dismantling the ADA’s wheelchair accessibility requirements?

[Saline9515]

Things like inclusion and other theories such as the one you describe are only possible in rich and technology-advanced societies. And are vulnerable to groups chosing to play against the whole society.

When you have to struggle for life, discriminating against some categories, such as disabled people is necessary for the whole group to survive. Animals do it, and humans in antiquity did it too, out of necessity. It's actually how evolution happens. Humans still do it to some extent when they choose how to mate : they discriminate.

[biztos]

Is the oldest child the most likely to survive, or is the winner simply the oldest surviving child?