Alzheimer's in particular does not reduce lifespan all that much; rather, it increases the resources that children and grandchildren need to use to care for the parent. So selection against Alzheimer's would presumably (we have very little evidence for any of this) be even stronger than selection against traits that, say, killed at 70.

Is actually caring for an Alzheimer's stricken relative a new phenomenon? Could it be that a hundred years ago, a chronically ill, continually deteriorating relative was just left in a room to waste away?

Professional Alzheimer's care is new;, without good professional work you're going to get sores and muscle atrophy and all kinds of other complications that can be fatal at old age. We've gotten very good at dealing with those, but not at actually curing the underlying disease. (Speaking from family experience.)

Maybe even more importantly, though, 100 years ago other, unrelated diseases of old age were likely to get you well before Alzheimer's really got bad.

Even today, people rarely die from Alzheimer's, because something else gets them first, as Alzheimer's is a very slowly progressing disease.

Increasing longevity to the point of incapacity may be a consequence of improved health care, rather than biological adaptation.

And while average life expectancy has been increasing for a long time (thanks to improved health care), the maximum life span has not. The oldest living people are still "only" about 115-122 years old.

Is this because "improved health care" only makes typical illnesses treatable/prentable whereas maximum lifespan (ie, the deteriation of cells/organs/etc with age) are not being focused on? Or is it because they are very challenging things to extend?

Primitive societies are known to abandon old people to die when they become a burden rather than an asset.

An ugly, indisputable fact. Saddening to see you downvoted.

some

What's a nomadic tribe to do with someone who can no longer keep up? When there is insufficient food (commonplace in older societies) who is going to get the food?

When resources get scarce, there are a lot of ugly realities.

You might do better to provide citations over argument.

"Traditional nomadic tribes often end up abandoning their elderly during their unrelenting travels. The choice for the healthy and young is to do this or carry the old and infirm on their backs — along with children, weapons and necessities — through perilous territory. Also prone to sacrificing their elderly are societies that suffer periodic famines. Citing a dramatic example, Diamond said Paraguay’s Aché Indians assign certain young men the task of killing old people with an ax or spear, or burying them alive."

http://newsroom.ucla.edu/stories/jared-diamond-on-aging-1505...

Thanks, exactly.