Even if you stay free of Alzheimer's disease, the normal aging process is fairly destructive to your brain. Neurons disappear, connections lose their strength, protein gunk builds up, and the whole brain shrinks. Areas controlling learning and memory are among the hardest hit. A new study claims that our crumbling brains aren't just a fact of normal aging. Instead, they may be unique in the animal kingdom, the result of an evolutionary bargain our species has struck.
Chet Sherwood at George Washington University led the study, which put humans and captive chimpanzees of various ages through MRI scanners. The humans ranged from ages 22 to 88. Chimps were between 10 and 45 years old, because 45 years is about as long as chimps can live in the wild (more on that in a moment).
In humans, the researchers found a pattern of decreasing brain volume throughout life that accelerated into old age. That pattern was missing in chimpanzees, whose brains seemed to maintain a consistent size.
Chimpanzees were used because they're our closest living relatives; we've been apart for only about 6 million years of evolution. The authors reason that because chimps' brains don't shrink as they age, our own brain degeneration must be a product of our recent evolution. We've developed brains that are big and energy-hungry, and to judge from our global population size, throwing our resources into our noggins seems to have been a good evolutionary strategy.
Since splitting from our ape relatives, we've also evolved longer life spans. Women, in particular, are a curiosity because they can live decades past their fertile years. Evolutionary biologists have hypothesized that keeping infertile elderly women around is no accident, because these grandmothers can bolster the success of their own genes by helping to take care of their grandchildren. The authors of the chimp study suggest that these helpful grandmothers are to blame for our degenerating brains: we've evolved long lifespans and brains that can't quite keep up.
The grandmother hypothesis, though, is hard to prove. And though 45 is elderly for a chimpanzee in the wild, the authors acknowledge that chimps under medical care in captivity can live into their 60s. Is a human today who lives into her 80s, thanks to medical care and disease prevention, comparable to a chimp in the wild? Or is a human "in the wild" better represented by someone in a southern African country with a life expectancy in the 30s or 40s?
If this study included chimpanzees at the true upper end of their age potential, it might provide more insight. The authors acknowledge that some previous studies have shown different results; for example, a study of brain mass that included chimpanzees up to age 59 did find some shrinkage with age.
The authors assume our damaging brain decline is a byproduct of evolution, but don't ask whether it might come from extending our life spans even further than evolution intended. Some perspective might come from studying another animal that no longer lives "in the wild": domestic dogs. Wolves live six to eight years in the wild, but many kinds of pet dogs can live for twice that long.
Even though they're not close to us in evolutionary terms, dogs age much like humans do. Their brains shrink in old age, especially in the prefrontal cortex and the hippocampus--the same areas that are particularly vulnerable in humans. Dogs develop cognitive problems and behavioral changes. Their brains even accumulate deposits of amyloid-beta, the protein gunk that appears in humans and is linked to Alzheimer's disease. Maybe our aging brains are not only the result of our exceptional smarts, then, but also of our domestication.
Sherwood, C., Gordon, A., Allen, J., Phillips, K., Erwin, J., Hof, P., & Hopkins, W. (2011). Aging of the cerebral cortex differs between humans and chimpanzees Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1016709108
Field of Science
-
-
-
Political pollsters are pretending they know what's happening. They don't.1 month ago in Genomics, Medicine, and Pseudoscience
-
-
-
The Site is Dead, Long Live the Site2 years ago in Catalogue of Organisms
-
The Site is Dead, Long Live the Site2 years ago in Variety of Life
-
Does mathematics carry human biases?4 years ago in PLEKTIX
-
-
-
-
A New Placodont from the Late Triassic of China5 years ago in Chinleana
-
Posted: July 22, 2018 at 03:03PM6 years ago in Field Notes
-
Bryophyte Herbarium Survey7 years ago in Moss Plants and More
-
-
Harnessing innate immunity to cure HIV8 years ago in Rule of 6ix
-
Do social crises lead to religious revivals? Nah!8 years ago in Epiphenom
-
-
-
-
post doc job opportunity on ribosome biochemistry!9 years ago in Protein Evolution and Other Musings
-
Growing the kidney: re-blogged from Science Bitez9 years ago in The View from a Microbiologist
-
-
Blogging Microbes- Communicating Microbiology to Netizens10 years ago in Memoirs of a Defective Brain
-
-
-
-
The Lure of the Obscure? Guest Post by Frank Stahl12 years ago in Sex, Genes & Evolution
-
-
Lab Rat Moving House13 years ago in Life of a Lab Rat
-
Goodbye FoS, thanks for all the laughs13 years ago in Disease Prone
-
-
Slideshow of NASA's Stardust-NExT Mission Comet Tempel 1 Flyby13 years ago in The Large Picture Blog
-
in The Biology Files
1 comment:
Markup Key:
- <b>bold</b> = bold
- <i>italic</i> = italic
- <a href="http://www.fieldofscience.com/">FoS</a> = FoS
Note: Only a member of this blog may post a comment.
Subscribe to:
Post Comments (Atom)
"even further than evolution intended"
ReplyDelete-obliged to point out the problem with this statement...otherwise, a thorough critique of the paper.
Keep up the good work!