'What we looked at is differences in the proportion of people who were living to be older,' Caspari said. Some individuals may have lived to great age, but at some point humans as a species began living longer on average than other primates and Caspari and Lee wanted to find out when and why.
They divided the fossils into two groups -- adults of reproductive age, which they settled on as 15 years, and adults that lived to be twice as old, 30, based on tooth wear.
In primitive societies, people are often grandparents at 30, Caspari pointed out.
'We found this proportion of older to young adults in the fossil record increased over time,' Caspari said.
'In the Upper Paleolithic that proportion just skyrocketed. It was just unbelievable. It increased five-fold. We didn't expect that.'
Caspari and Lee rechecked their numbers and analysis.
'But then we started to think about it and thought we really shouldn't be surprised, because there is a behavioral change that took place over time at the same time,' Caspari said.
'You start to see a change in symbolic behavior. You see art. You see a large number of people being buried with jewelry, with body ornaments.'
Perhaps around this time people started to value and take care of the weak and the old, and in turn benefited from their help and experience, Caspari sad.
This could be when the uniquely human condition of menopause evolved and started to have an effect, Caspari said. Women not burdened by childbearing could focus on their grandchildren and other kin.
'We live in a society that is so geared toward younger people. It is nice to realize that it might be older people that make us human after all,' Caspari said.
Now if only the economic rationalists had a decent grip on politics in the Upper Paleocene we could have avoided centuires of economic inefficiency in caring about the weak and the old. Damn!