There are many instances of braces and artificial limbs or that were found or fossilised bones that showed crippled people that grew into old-age, which provides evidence that people cared for 'non-productive' members.

Finding evidence that disable people existed does not provide evidence that they were not able to contribute in some way. It's incredibly ableist to assume they couldn't.

In the context of a pre-industrial society? I doubt it. In a hunter gatherer-society? I doubt it even more. people with certain skills (e.g. tool making, music, cooking maybe..) certainly, but not for a lot of people.

However, decent human beings do not value other human beings purely on the basis of their economic contribution. Someone might be a net cost, but a decent society still looks after them.

You're missing things like making clothing (tanning, sinew, etc) , gathering wood, etc. You can be missing an arm or leg and still contribute to those.

Assuming that disabled people are worthless when they are not able to contribute to the group is even worse.

I never said that. I'm merely countering the claim that disabled people couldn't contribute.

I say this with all due respect and as someone who is struggling to envision their own ability to meaningfully contribute in the likely future:

Nature is ableist. Humanity rises above it to the extent that we can, but ...

I think we have a skewed perception of ability, now that we’re connected via the internet to the whole rest of humanity.

Nature is ableist in a lot of ways… if you had diabetes in some ancient tribe you’d basically be screwed. But if you had an amputated leg, I dunno. You could still be the best flint knapper in the tribe.

I mean, think of your extended circle of friends and acquaintances, your 100 “closest” friends. In particular, think back on the community grew up in, if you’ve subsequently moved to a tech hub that accumulates rare talent. I bet picking through your hobbies there are a couple potentially useful things that you’d be a top-tier contributor in. Most people are really bad at almost everything they don’t do, after all.

I’m not going to engage in some prehistoric idealism. The past was pretty brutal. But we’d probably all die by getting little infected cuts, not because we were abandoned by our tribes.

The cynic in me wonders if it's because they were family members of the leader so got better health care.

Indeed. If one is crippled their 'value' for the tribe doesn't suddenly disappear. A person has their wit, their positive spirit, their wisdom and skills, their empathy, care and understanding for others that is important for the tribe's wellbeing. Etcetera.