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If, like me, you are on the wrong side of 60, you have probably noticed these "increasingly older moments", more and more frequent and sinister. What did I look for when I entered the kitchen? Have I already pulled out the trash? What is the old name of what name is it still?
Resignation is one of the possible reactions to aging: you have passed your expiry date. You may have heard that centuries ago, the average life expectancy was only about 40 years old. So you might think that modern medicine and nutrition prevent us from going beyond our limit of evolution. No wonder the machine is starting to break down.
In fact, recent research suggests a very different picture. The shorter average life expectancy of the past is mainly due to the fact that many more children have died young. If you have spent the childhood, however, you could live well in your sixties or beyond. In today's hunter-gatherer cultures, whose way of life is closer to that of our prehistoric ancestors, it is quite common for people to live to age 70. This contrasts with our close relatives of primates, chimpanzees, who live very rarely beyond their fifties.
There seems to be only human genetic adaptations that keep us in old age and help us protect ourselves from cognitive decline. This suggests that the last decades of our lives are there for a reason. Humans are animals with unique culture. we depend primarily on the discoveries of previous generations. And the elderly are well placed to pass on their accumulated knowledge and wisdom to the next generation.
Michael Gurven, an anthropologist at the University of California at Santa Barbara, and his colleagues studied aging among Tsimane, a group of the Bolivian Amazon. The Tsimane live in a way that is more like the way we used to live in the past: hunting, gathering and small-scale farming of local food, relatively little schooling or little frequented by markets and cities. Many Tsimane are between 60 and 70 years old, and some even reach 80 years old.
In an article published in 2017 in the journal Developmental Psychology, Professor Gurven and his colleagues entrusted more than 900 people in Tsimane with a battery of cognitive tasks. Older members of the group had a hard time doing things like remembering a list of new words. But the researchers also asked their subjects to quickly name as many fish and plants as possible. This ability has improved with the aging of Tsimane. It peaked around the age of 40 and remained high even in old age.
Research on Western urban societies has produced similar results. This suggests that our cognitive strengths and weaknesses change with age, rather than undergoing a general decline. Elements such as short-term memory and speed of treatment – so-called "fluid intelligence" – are in their twenties and decrease precipitously with age. But "crystallized intelligence" – what we actually know and how we can access that knowledge – improves up to the average age, and then declines much more slowly or not even from the all.
So when I forget what happened yesterday and I can tell my grandchildren and students alive stories about what happened 40 years ago, I may not be falling apart. Instead, I may be doing exactly what evolution had intended to do.
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