Anthropologists are not often in the news, and they are even more rarely in the spotlight for discovering what might be a connection between a human ill and how other people live. But anthropologist Ben Trumble was recently profiled (or his work was) in The New York Times for suggesting that Alzheimer's is so common in Western culture because we are devoid of regular parasitic infection.
Trumble's work comes from a long-term and collaborative study of the Tsimane of Bolivia. The Tsimane live in savannas and forests and they make a living by growing things to eat, foraging and hunting. Although many South American cultures have been affected by missionary or governmental zeal to acculturate them into Western ways, the Tsimane have resisted and maintain their identity and way of life.
Along line of Western researchers have spent time with the Tsimane since 2001 and their main focus has been their health and welfare over the human life cycle. Trumble focuses and contrary to what Westerners might expect, once successfully past childhood, many Tsimane live into their 90s and they are physically very healthy. Tumble became especially interested in the possible role of Alzheimer's and dementia in their lives.
Tumble put together what is currently known about the genetics and biology of Alzheimers with the particular life circumstances of the Tsimane and came up with the possibility that being subject to repeated parasitic infections repeatedly might have a key to understanding why some people exhibit Alzheimers and others do not.
Working with the Tsimane, Trumble compared the incidence of the ApoE4 gene, which in a double blast increases the risk of Alzheimers tenfold in the West, to results of cognitive tests with his volunteers. He found that Tsimane elderly who had a copy of the gene in fact did better on those tests than those with no ApoE4.
But that's not the really surprising part. Trumble also compared these results, genetic and cognitive, with parasite load. It seems that those with the gene in single or double form and parasites retained their mental acuity while those without parasites and even one copy of ApoE4 often did not. They looked like Westerners in terms of cognitive ability.
In other words, what we now see as a "bad" gene might have been protective and "good" when our ancestors lived a less parasitic life. Those genes might have evolved to protect our aging brains from parasites and now they are, instead, damaging brain cells because their evolutionary environment has changed.