March’s Nature Reviews Cancer has an article out by Mel Greaves on Darwinian Medicine: A Case For Cancer. While I cringe at the label ‘Darwinian’ (what’s wrong with Evolutionary Medicine?), the paper is great for those people who mistakingly think that a thorough understanding of evolution is dispensible for the medical profession.
What is evolutionary medicine, however? As Greaves writes it:
The essential tenet of the new discipline of evolutionary or Darwinian medicine is that susceptibility to malfunction and disease must in part reflect historical or evolutionary legacies. The corollary is that we might then benefit from stepping back to take a broader look at human history and our protracted evolutionary trajectory. Even a cursory consideration of human anatomy reveals structural imperfections that are pregnant with potential for malfunction. For example, no intelligent designer would place the optic nerve and retina or prostate and urethra in the anatomical relationships in which we find them. The reality is of course that we have not been ‘designed’ or ‘engineered’ at all. The evolutionary processes involved in the diversification of molecules, cells, tissues and physiological processes rely on options generated randomly from previous templates. This is coupled with the selection of beneficial traits, by contingency or chance, or neutral drift. Evolutionary biologists continue to debate the relative importance of the mechanisms of selection, particularly as claims that traits were positively selected (the adaptionist argument) cannot always be substantiated. Irrespective of these uncertainties, the processes involved will inevitably result in ‘designs’ that have constraints or limitations on board, and trade-offs, collateral damage or negative impacts.
And in making the case for an evolutionarily-informed approach to cancer, Greaves explains how stem cells may be a cellular source of much of the trouble. Evolution, perhaps, may have inadvertantly provided stem cells with a ready-to-go set of pre-malignant traits.
Further, Greaves suggests:
For Homo sapiens as a species, this can also have profound consequences. Over the past 200,000 years or so, humans have intermittently been selected as genetic variants by the selective forces of lethal epidemics or massive environmental challenges. Additionally, mutations become prevalent, over centuries, through founder effects, as is likely to be the case for common breast cancer susceptibility mutations in BRCA1 in Ashkenazi Jews. But humans are especially unique in their rapid social and cultural evolution, largely divorced from fitness tests for competitive adaptability or genetic selection
And all of this because of evolutionary tradeoffs - what is beneficial early in development, or long ago in our ancestory, may one day become lethal insults that physicians need tend to.
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