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
Very interesting….and he doesn’t look a day over 65! I always think keeping your mind active and being interested in many, many things helps to ward off senility but then again, when it runs in one’s family it’s a bit of a worry! And that’s rather shocking on how they treat chimps….why am I not surprised, however?
Thanks, Audrey. I think Cheetah is holding up rather well, too. I agree that keeping our mind active helps to ward off senility. However, there are limits to how long we can expect to live and still have a fully functioning brain. It seems to be a design parameter. Under normal conditions in the wild, our bodies would give out long before the brain would. We are noticing this limitation of the brain more now, because we are able to stay alive much longer under artificial conditions. Even in the US , in the first half of the 20th century, it was quite common for the edlerly to die of pneumonia. It doesn’t happen that much anymore.
It also does depend on genetics. I have ancestors on both sides of my family who lived into their eighties and nineties, and were fully functioning and healthy. I think one problem with the longer life expectancies is how people are not eating very healthy. Type II diabetes is on the rise in the US, and it could be curbed if people were a bit more healthy and active. It sounds like chimps are not always treated humanly in these studies. It is good that you are pointing these things out.
Sweetbearies, I agree that personal longevity is something that has genetic components. However, those people whose body doesn’t give out first end up dying of an aging brain syndrome, and among those who die this way, there tend to be a majority who survived their fifties. So if most chimpanzees do not get to be fifty for circumstantial reasons, then it says nothing about their likelihood of eventually succumbing to brain degeneration if they were kept alive longer.
Yes, it is a shame that chimps are not always treated humanely.
This is a very interesting article. I think genetics is a big component. Then, there is also rain damage for heavy drinkers or drug abusers. A healthy lifestyle should help. but they always tell you as you age to keep your brain active, working puzzles and so forth. I hate the thought of chimps not being treated humanly.
Pamela99, thanks. I agree that we can hasten brain degeneration by taking substances, like alcohol or other drugs, that diminish the brain’s optimal functioning. We can also put off the eventual degeneration of our brain by leading a healthy lifestyle and keeping an active mind. But the top most limit of how long we can keep a healthy brain is probably a biologically determined parameter. Genetics certainly plays a role. What doesn’t seem reasonable is to compare the brains of chimpanzees who die early from other causes to the brains of humans who have been spared that kind of death, only to find that their brains are failing them. It’s like comparing apples and oranges.
I agree that it’s a shame more chimps in captivity are not afforded the lifestyle that allowed Cheetah to thrive well into old age.
“Which is just another reason we should not trust authority nor publicly fund scientific research.”
I like your conclusion better than theirs! 😀
Thanks, Suzanne! I’m glad we see eye to eye on this.
In the U.S. you live on average to 78.2 compared to 39.6 in Swaziland. The reason you live about twice as long is because of publicly funded research has led to decrease in infectious diseases. Why so cynical about someone who has spent their life becoming an authority? That worries me more than your conclusion about the article. Skeptical, yes (as are all scientists which is why we have such a long and improved life) cynical, we try not to be.
Jim, I think as a scientist you should realize that your statement that public funding for research is the direct cause of the longer average lifespan in the US versus Swaziland is hardly incontrovertible. How would you go about proving that? How would you separate the contributions of publicly funded versus privately funded research? How would you control for better nutrition (or at least more nutrition, calorie-wise) in the the US versus Swaziland because of the free enterprise system that, while very much eroded, still functions in the US to some extent? How would you control for lower number of deaths by violence in the US?
I think that my main point, that chimpanzee lifespans differ from those of humans primarily due to environmental factors, is a sound one. You don’t seem to disagree with that. But you apppear to have a problem with my general orientation vis-a-vis health and public funding for research.
That I have a bias is true. I am a private researcher, and every tax dollar that is taken from me, and from my neighbors and my supporters, goes to fund competitors and colleagues who are not even allowed to collaborate with me, on pains of having their federal funding cut off. But I also have an overall bias in favor of free choice, and I think one of the least appreciated parts of this article is the one that discusses the general health of people living in Swaziland. They die young, but they spend most of their lives healthy.
Have you ever asked yourself whether the goal of applied medical research is to promote overall health in a population or to create a population dependent on artificial health care for their day to day survival?
This is a terrific commentary, and I too like the conclusion at the end. I remember very distinctly from “How We Decide” that experts actually are more likely to make incorrect predictions than amateurs are, because the experts tend to be more concerned with their own reputations than with seeing what the evidence says. (That’s a rather sweeping paraphrase, I know.)
I was also quite interested to read here that human brains are more swollen and slower in processing speed than chimp brains are. That reminded me of having read that people with ADD have a smaller PFC (I think!) than other humans do; I wondered whether that could account for the higher speed of thought of the ADDer?
And I have surmised that the much-touted “logic” of humans is really primarily – initially – a process of slowing down our thinking in order first to deconstruct it, then to analyze it, and finally to reconstruct in what we hope will be meaningful ways. Well, there’s too much to say on that topic for this space, so I’ll stop for now. Anyway, thank you for this article!
Thanks, Fan! Some experts, though by no means all, are so taken with their original hypothesis that they forget to check for simpler explanations.
Yes, your observation about ADD makes sense to me. It may not be just about the size of the prefrontal cortex, though. It seems to be overall connectivity and speed of transmission in a smaller brain. My observation of Bow is that instead of being slower than we are at thinking, he’s actually much faster. We had to watch videos of his responses to us mutliple times and had to slow them down, before we could notice what he was doing. This made communication in real time difficult.
I agree that when dealing with logic, we tend to slow down the process of our thinking, so that we make the conclusions we arrive at subconsciously available for conscious observation.
I am sad to report that Cheetah has died. He was eighty.
http://www.hollywoodreporter.com/news/cheetah-dies-tarzan-chimpanzee-276487
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