Yesterday I came across a science news story released by the establishment. In big headlines, it read: “Evolution of Human Longevity Led to Large Brains and Brain Shrinkage”. Always interested in comparative studies of chimpanzees and humans, I eagerly read the story. I was even almost prepared at the outset to believe that it was going to contain a big revelation. I thought, well, we do have swollen brains with poor connectivity, compared to chimpanzees, which accounts for our slower processing rate and our ability to concentrate on minutiae. It might be possible that during old age the swelling goes down. After all, some immune disorders tend to dissipate as we age. But it didn’t turn out to be anything like that.
So what did the article actually say? Here is their reasoning in a nutshell. Chimpanzees in the wild rarely survive past the age of forty-five. In captivity, they can live to be as old as sixty. Humans, on the other hand, live well into their eighties. So what did the researchers do? They compared humans from age twenty-two to eighty-eight and chimpanzees from age ten to age fifty-one. And what did they find? Humans had a lot of brain shrinkage in late old age, whereas chimpanzees did not. (To read the article in Science Daily, click here.)
And what was the long ranging conclusion? That humans due to the evolution of their brain and the evolution of their longevity, both of which are deemed to be biological facts, are more susceptible to diseases of senile dementia, such as Alzheimers.
I think this is a flawed conclusion. It is not because I have access to more information than the researchers. After all, they got to study larger populations of humans and chimpanzees than I ever have had access to. They also had magnetic resonance imaging, a big research budget and lots and lots of technology to play with. So I don’t question their bare-bones facts. I just don’t understand how anyone could draw that conclusion from those facts.
Our longevity as humans is not primarily a result of evolution. Sure, some individuals do live much longer than others, and there are probably genetic facts that account for the rare person who remains healthy well past the age of one hundred. But by and large, the longevity of populations of humans is much more tied in to environment than genetics. Health care has an important impact on both lifespan and health during lifespan. In developed countries, the lifespan is longer, but the health issues that people have to deal with are much more serious. In other words, they stay alive longer, but they spend a lot more of their life being seriously, chronically sick. In countries with very little health care, humans tend to live about the same as chimpanzees in the wild, but they spend most of their life being healthy. There are no people with senile dementia in countries where humans die while still active and in their prime.
The life expectancy for a human being in Swaziland is 39.6 years. How many of those years can a human in Swaziland expect to stay healthy? 38.1. This translates to a “healthy life expectancy” of 96.2 %. That means that for 96.2% of their lives, the average Swaziland resident will be really, really healthy and will not require any kind of medical care. Let’s contrast that with a human being living in the U.S. . The average human being in the United States of America can expect to live to the ripe old age of 78.2, but he stops being healthy at around age seventy. This allows for a healthy life expectancy of 89.5%. But, of course, not every human in the United States dies as young as 78.2. Many live much longer than that. And the longer a human lives, the more likely he or she is to experience brain degeneration and shrinkage. (Want to know where I got this information? Click here.)
Now what about chimpanzees? Most chimpanzees live under much harsher conditions than humans, even when they are in captivity. The average zoo or research facility doesn’t really care what happens to the chimp, once he has served his purpose. Yes, they do give medical care, but often without any regard for what is best for the chimpanzee. For instance, they will use anesthesiology to make a chimpanzee unconscious just for a routine medical examination, when the chimpanzee is not sick, because they are afraid for their own safety. This routine use of very dangerous drugs takes a toll on the health of the chimpanzee. Research facilities also do things intended to harm chimpanzees, so it’s no wonder they do not live that long on average in captivity.
But did you know that Cheetah, a chimpanzee who starred in the Tarzan films with Johnny Weissmuller, is still alive in his late seventies?
So to recap: the human lifespan is to a great degree determined by the environment in which the human lives. We cannot ascribe the differences in human lifespan in Swaziland from the human lifespan in the United States to evolution. Neither can we suggest that Johnny Weissmuller’s co-star, Cheetah, is necessarily more evolved than the average chimpanzee in the wild or in a zoo. Lifespan is very much subject to living conditions.
It does not make any sense to compare the brains of fifty year old chimpanzees with the brains of eighty year old humans and to marvel at how much degeneration of the brain has taken place in the humans. The brains of fifty year old chimpanzees should be compared to the brains of fifty year old humans.
So who did this study? The National Science Foundation partially funded the work of Chet Sherwood, an anthropologist at The George Washington University in Washington, D.C., and a team of scientists from seven other U.S. universities. The authority level of this team is very high. Which is just another reason we should not trust authority nor publicly fund scientific research.
© 2011 Aya Katz