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Recently a team of researchers investigating the relatively low rate of cancer experienced by African elephants discovered that the elephants possessed multiple copies of gene P53.
This finding has received well-deserved publicity here, here and elsewhere. Unfortunately, in one of those articles a co-author of the JAMA paper was quoted as saying "By all logical reasoning, elephants should be developing a tremendous amount of cancer, and in fact, should be extinct by now due to such a high risk for cancer ..." Although he goes on to say that of course elephants didn't all die of cancer because they have powerful defenses against it, this scientist is repeating the faulty logic underlying "Peto's Paradox" which has led to attempts (here, here and here) to "solve" what some perceive to be a puzzling mystery.
As I explained in my May 2014 posting, where I amplified points made in Chapter Nine of my 1992 book Cancer Selection, in animals with immune systems capable of killing cells that were already transformed to the cancerous state, larger bodies automatically provide more efficient cancer defense than smaller bodies for the simple reason that they muster greater numbers of individual cancer-killing units, e.g., T-cells. If those larger armies of cancer-fighters actually eliminate threats by completely destroying the earliest (i.e., the smallest) populations of malignant cells, then the result is lower rates of detectable cancer. I am not ruling out the possession of other cancer defenses in some larger animals but immune systems capable of destroying cells already transformed to the malignant state are fundamentally different from defenses that prevent the initiation of cancer-inducing mutations. Post-transformational defenses function as fail-safe mechanisms which means that the gene pools could survive with lowered pre-transformational defenses that worked by preventing the origin of cancer. This is what I wrote in my 1983 Letter:
The evolution of efficient cancer-specific immunological defenses in all vertebrates would have enabled those species to adapt characters, functions, etc., which might have increased the incidence of cancer initiation. The following all suggest the lowering of first line defenses against cancer in vertebrates: increased mitosis as evidenced by large body size and extended pre-reproductive life, increased exposure to radiation as the result of migration from aquatic to terrestrial habitats, and the elimination, in many mammalian species, of opaque external protection from UV radiation. [Emphasis added.]
More evidence of how erroneous is the "large animals ought to have more cancer" notion is evident in comparing two animal species whose experience with cancer is far better known than that of African elephants and blue whales. I refer to mice and to humans. As I mention in Chapter Eleven of Cancer Selection, investigators for the United States' National Cancer Institute found cancerous tumors in more than 40 per cent of a randomly-selected sample of wild mice. If we were to apply the logic implicit in the suggestion "larger animals makes no sense" then the human lineage ought to have been terminated by cancer long ago: the typical mouse weighs one ounce and the typical human, 2,400 ounces (150 pounds); mice reach breeding age in 6 to 8 weeks, humans, no earlier than 10 years (520 weeks).
Moreover, no one convinced that evolution actually happened needs to be reminded that huge populations of enormous animals—dinosaurs—many of them much larger than elephants, thrived for more than one hundred million years. And, yes, dinosaur cancer did occur.
This is what I think: If "all logical reasoning" tells you elephants, blue whales, humans and dinosaurs ought not to have existed I suggest, with all due respect, that your "logical reasoning" is worthless.
As I explain in Chapter Three my theory which was originally published with the peer-reviewed title Cancer and Evolution: Synthesis says that—without exception—all Bilaterian gene pools produced animals equipped with defenses against cancer, powerful defenses capable of ensuring that sufficient numbers of animals lived to breeding age; all populations of complex animals whether equipped with small bodies or large bodies, long or short life spans, in thriving modern lineages or in lineages that went extinct in the distant past were replete with cancer defenses. There are no paradoxes.
As I explain in Chapter Three my theory which was originally published with the peer-reviewed title Cancer and Evolution: Synthesis says that—without exception—all Bilaterian gene pools produced animals equipped with defenses against cancer, powerful defenses capable of ensuring that sufficient numbers of animals lived to breeding age; all populations of complex animals whether equipped with small bodies or large bodies, long or short life spans, in thriving modern lineages or in lineages that went extinct in the distant past were replete with cancer defenses. There are no paradoxes.
However, my theory does provide a basis for tentatively identifying other animals that might possess unknown cancer defenses. I will mention some of them in my next posting.
Further Reading.
I express my disagreement with the findings of other professional investigators in this posting: Cancer Discovered in Hydra?
Comments and question are welcomed here.
At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and the 1992 Nature review of my book.
Copyright © 2015 by James Graham
This page was archived at Way Back Machine on October 19, 2015.
Further Reading.
I express my disagreement with the findings of other professional investigators in this posting: Cancer Discovered in Hydra?
Comments and question are welcomed here.
At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and the 1992 Nature review of my book.
Copyright © 2015 by James Graham
This page was archived at Way Back Machine on October 19, 2015.
Comments and questions are welcomed here.
At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and the 1992 Nature review of my book.
Copyright © 2015 by James Graham
This page was archived at Way Back Machine on June 29, 2015.
- See more at: http://cancerselection.blogspot.com/2015/06/updated-visitors-to-this-site-and-their.html#sthash.OU3IBbTU.dpuf
At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and the 1992 Nature review of my book.
Copyright © 2015 by James Graham
This page was archived at Way Back Machine on June 29, 2015.
- See more at: http://cancerselection.blogspot.com/2015/06/updated-visitors-to-this-site-and-their.html#sthash.OU3IBbTU.dpuf
Comments and questions are welcomed here.
At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and the 1992 Nature review of my book.
Copyright © 2015 by James Graham
This page was archived at Way Back Machine on June 29, 2015.
- See more at: http://cancerselection.blogspot.com/2015/06/updated-visitors-to-this-site-and-their.html#sthash.OU3IBbTU.dpuf
At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and the 1992 Nature review of my book.
Copyright © 2015 by James Graham
This page was archived at Way Back Machine on June 29, 2015.
- See more at: http://cancerselection.blogspot.com/2015/06/updated-visitors-to-this-site-and-their.html#sthash.OU3IBbTU.dpuf
Comments and questions are welcomed here.
At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and the 1992 Nature review of my book.
Copyright © 2015 by James Graham
This page was archived at Way Back Machine on June 29, 2015.
- See more at: http://cancerselection.blogspot.com/2015/06/updated-visitors-to-this-site-and-their.html#sthash.OU3IBbTU.dpuf
At this site you will find links to additional material including my original Letters to the Journal of Theoretical Biology and the 1992 Nature review of my book.
Copyright © 2015 by James Graham
This page was archived at Way Back Machine on June 29, 2015.
- See more at: http://cancerselection.blogspot.com/2015/06/updated-visitors-to-this-site-and-their.html#sthash.OU3IBbTU.dpuf
