Cancer: The cost of being smarter than chimps?

John McDonald, chair of the School of Biology and chief research scientist at the Ovarian Cancer Institute, is testing whether the cognitive superiority of human's brains over chimps has lead to an increased propensity for cancer. Credit: Nicole Cappello/Georgia Tech

Are the cognitively superior brains of humans, in part, responsible for our higher rates of cancer? That's a question that has nagged at John McDonald, chair of Georgia Tech's School of Biology and chief research scientist at the Ovarian Cancer Institute, for a while. Now, after an initial study, it seems that McDonald is on to something. The new study is available online in the journal Medical Hypothesis and will appear in the forthcoming issue of the journal.

"I was always intrigued by the fact that chimpanzees appear to have lower rates of cancer than humans," said McDonald. "So we went back and reanalyzed some previously reported gene expression studies including data that were not used in the original analyses."

McDonald and his graduate students, Gaurav Arora and Nalini Polivarapu, compared chimp-human gene expression patterns in five tissues: brain, testes, liver, kidneys and heart. They found distinct differences in the way apoptosis — or programmed cell death — operates, suggesting that humans do not "self-destroy" cells as effectively as chimpanzees do. Apoptosis is one of the primary mechanisms by which our bodies destroy cancer cells.

"The results from our analysis suggest that humans aren't as efficient as chimpanzees in carrying out programmed cell death. We believe this difference may have evolved as a way to increase brain size and associated cognitive ability in humans, but the cost could be an increased propensity for cancer," said McDonald.

Like all evolutionary hypotheses, this can't be proven absolutely, according to McDonald. However, his lab has recently obtained additional direct experimental evidence consistent with the hypothesis that apoptotic function is more efficient in chimps than in humans.

Source: Georgia Institute of Technology

   

• codesuidae - Jun 10, 2009
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  How do they show that ineffective apoptotic function contributes directly to increased brain size? If it does, does it contribute to increased size of other aspects of the body as well?
  
  Do they have plans to show how ether increased apoptotic function in humans results in smaller brain size or decreased function in chimps results in larger brain size (and more cancer)?
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• Olson - Jun 10, 2009
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  There's probably a huge amount of factors influencing rates of apoptosis that are not controlled for in this kind of interspecies comparison experiment.
  
  About the evolution of the brain, seems like less apoptosis would likely not be selected for since it is required for proper structuring of brain by pruning out excess neurons that are not integrated in functioning networks.
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• El_Nose - Jun 10, 2009
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  In realility aren't we really talking about chemical pathways and processes. I think what is being suggested merely by the article is that the chemical signatures are harder to come by in humans to trigger cell death. That the basic pathway is less complex in chimps and that the added complexity seems to allow for other chemical pathways to exists that allow for larger brain mass and complexity.
  
  -- Now whether they are right , or this is true will be in the science -- when biologists can lay down a close approximation of the full path of apoptosis (which i believe is close to complete outside of recognizing which genes code for the protien bindind) but then we need to fully understand all the chemical process that go into growing a brain. We may observe but never really know.
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• mo411 - Jun 10, 2009
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  One of the fundamental keys to cancer is becoming how cells communicate with one another. What if the aforementioned is an artifact of humanities improved internal cell to cell communications? We are more adaptable because of cell to cell communication which one might conclude is an elevated anatomy for the cell and groups of cells. This intern might lead to communication breakdown in the request for cells to self-destruct... once we find this key will we use it for growth or as a new weapon to manipulate the populous and to the finder of the key do you pause and contemplate the ramifications of your discovery?
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• mongander - Jun 10, 2009
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  Do dolphins have higher rates of cancer because of their large brains?
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• E_L_Earnhardt - Jun 11, 2009
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  The ape's coarse hair radiates more HEAT ENERGY!
  His bone mass CONDUCTS more inner heat outward!
  His RESPERATION far exceeds the human!
  COOKED food is a rarity! He consumes lots of water!
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