Human life expectancy was halved or worse by the rise of cities and "civilization".

There is rising fossil evidence of humans living 60+ years prior to the neolithic age.

The paradigm of human interaction prior to cities was to live in nomadic bands of 100 members or less, largely a group of families, and egalitarian in social structure.

These groups were widely interspred, and rarely contacted each other. Anthropologists suggest that a band might come across another band once every few years.

There is little fossil evidence of death by disease prior to the rise of cities.

It is believed that with humans population density so low, harmful viruses and bacteria had no vectors to spread between bands, and a single band could develop an immunity before the illness could pass beyond the band and mutate to a form that is unrecognized by the human immune system. Or they'd just die, and take the disease with them without spreading it.

I could go on and on. E.g. why cities were bad for water quality and humans in cities predominantly drank wine instead of water, due to the alcohol killing the bacteria that was thriving in unpurified water.

FYI.

Civilization is only now, 40,000 years later reaching and equivalent life expectancy.