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Multi-level Selection and the Evolution of Aging, I

 

Darwin’s legacy, his gift to science is the idea of a creative competition that selects the strong, the robust, the fertile, and thereby ratchets the complexity of life.

But does this contest take place one individual against another?  Or more collectively, species against species?  Do whole ecosystems compete with other ecosystems, or is it “every gene for itself”?

These are questions which it seems Darwin never posed.  Apparently, he did not think of these different modalities of natural selection as antagonistic or mutually exclusive, because at different times, in different books, he described the mode of competition variously, as suited the trait or natural phenomenon that he was seeking to explain.

The “selfish gene” idea in particular did not come from Darwin; in fact, Darwin knew nothing of the mechanism of biological inheritance.  The words “gene” and “genetics” were coined by Gregory Bateson 20 years after his death, and though Gregor Mendel with his pea plants was working out the fundamental laws of heredity contemporaneously with the Origin of Species, yet Darwin never knew of this keystone discovery in his lifetime.

Curious, then, that in the 20th Century, Darwin’s legacy came to be associated with the “selfish gene” picture exclusively.  In the 1970s, this rather narrow picture of evolutionary competition came to dominate evolutionary theory, and still does so today – not without some controversy and vigorous dissent.

The story of how this came to pass is one of the great object lessons in the history of science because, in my view, a great scientific community took a wrong turn, and has wandered in the desert forty years.  Twentieth century evolutionary theory was grown on the foundation of laboratory experiments, and is just now finding its way back to a picture that is grounded, more appropriately, in observations of nature.

But this is a blog about aging.  Why are we diverting into a morality tale about the controversial details of how Darwinian selection operates in nature?  Because aging has turned out to be a glaring exception to the “selfish gene” picture.  Because this wrong turn in evolutionary theory has affected our conception of aging generally – not just medical research and long-term social policy, but standard care for heart disease, cancer, PD and dementia has been affected.

 

Evolutionary Altruism

In fact, for most features of biology, it doesn’t matter much if we think in terms of the fitness of the individual or the fitness of the community, because they amount to the same thing.  A swift herd of gazelles is no different from a herd of gazelles, each individually evolved to be able to run fast.  In most cases, collective fitness is simply the sum of individual fitness.  It is only in those areas where the good of the individual and the good of the community come into conflict that the distinction between individual fitness and group selection becomes interesting and important.  The subject is called “evolutionary altruism”, and it includes

  • the “sentinel” meerkat who risks her own skin by standing tall and calling loudly to warn the mob of a nearby eagle (ref)

  • yeast cells that commit suicide en masse when a colony is starving, 95% turning themselves into food for the remaining 5 (ref)

  • many kinds of mammals have been observed to adopt an orphaned baby, feed it and raise it with their own. (ref)

Aging is a trait that destroys individual fitness, but it is beneficial for the community, and aging is an essential ingredient in the recipe for a stable, robust ecosystem.  Aging is an extreme example of evolutionary altruism because nearly everyone bows out on a fixed timetable, leaving a big chunk of their fitness on the table, and because there is no particular beneficiary of the altruism, only a vacancy in the niche that could be filled by anyone, really.

History of Evolution: how did we get here?

Darwin was primarily a naturalist, not a theoretician.  He traveled the world collecting examples, and described his theory entirely in terms of stories and observations of animals and plants.  Following Darwin fifty years later in their native England, R. A. Fisher was a giant who gave shape both to evolutionary theory and to all of modern probability and statistics.  Fisher was a mathematician with only a shallow knowledge of biological phenomena.  Decades before computers were available, he worked with equations that required broad, simplifying assumptions to be solvable.  Yet his conception of how evolution works has molded  evolutionary theory continuing to this day.  Many biologists forget that the simplifying assumptions were made for computational convenience, and have come to regard them as fundamental laws of nature.

What is worse: in one of the most crucial accidents of scientific history, it happened that Fisher was a passionate social Darwinist.  In the early years of the 20th Century, eugenics was a science and social philosophy with a great deal of currency, especially among the Fabian Society, a visionary, liberal social movement that sought to reform the traditional, rigid British social structure.  (It was not until 30 years afterward, due to Hitler’s atrocities, that eugenics was discredited, and the very word became anathema to polite society.)

Fisher believed that protecting and improving the human genetic legacy was the most important social imperative of his time.  Fear of the ongoing dilution of the gene pool inspired a passion comparable to today’s movement against global warming.  Fisher thoroughly conflated the ideas of “good genes” with wealth and social standing.

We must face the paradox that the biologically successful members of our society are to be found principally among its social failures, and equally that classes of persons who are prosperous and socially successful are, on the whole, the biological failures, the unfit of the struggle for existence, doomed more or less speedily, according to their social distinction, to be eradicated from the human stock…In societies so constituted, we have evidence of the absolute failure of the economic system to reconcile the practice of individual reproduction with the permanent existence of a population fit, by their mutual services, for existence in society. (ref)

Though his inventiveness and mathematical proficiency made him uniquely brilliant, Fisher was ideologically very much in the same league with social Darwinsts of his day.  Ever since Francis Galton and Herbert Spencer in the 19th Century, Darwin’s theory has been misappropriated in the defense of class privilege and the excesses of capitalism.

The dominant view, continuing to this day, is that there is no such thing as “group selection”, that cooperation in biology is always illusory and that the “selfish gene” explains all.  This picture has been shaped and tainted by social Darwinism and capitalist ideology.  In the 1970s and 80s, contemporaneously with the discrediting of group selection in all its forms, unregulated, pure capitalism was also emerging as the one true economic system.  Both these views seem to me dogmatic, but they are entrenched and fiercely defended.  Every researcher who has written about multi-level selection has tales to tell about journal editors and referees who have refused even to consider their work.

In contrast, the new view – the emerging view as articulated by David Sloan Wilson, persisting through his long career – the emerging view in the evolutionary community is that the “selfish gene” is but one mechanism among many.  Darwinian selection takes place on multiple levels simultaneously, and in those interesting cases where there is a conflict among different levels of selection, a detailed analysis is necessary to see whether it is the collective good or the selfish interest that wins out.

 

Theories of aging derive from beliefs about evolution

We have learned well that “nothing in biology makes sense except in the light of evolution,” [Theodosius Dobzhansky]  Evolutionary dogmatism has bequeathed to gerontology a false and distorted picture of what aging is, where it comes from and how it works. This mistaken foundation has led an entire community of researchers astray, and medical research has been (mostly) blind to one of the great opportunities for life-saving science.

Just because aging as an altruistic trait is so hard to understand theoretically, biologists have been reluctant to acknowledge abundant evidence that aging is programmed into our genes, without tradeoff or benefit to the individual.  One result of this denial is that there are some simple ways to thwart the aging genes, to turn them off, but research on these strategies has remained unfunded in a backwater, because most scientists think it can’t be so simple, and “there must be a catch”.  (I have written about some of these here andhere and here.)

I’ll continue this topic next week, focusing more on aging, how our understanding has been shaped by evolutionary ideology, and how an alternative evolutionary explanation for aging opens new possibilities for practical medical applications.

 

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this post originially appeared on Josh’s blog here: http://joshmitteldorf.scienceblog.com/

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