Multilevel Selection and the Evolution of Altruism;
Aging as an Altruistic Adaptation

academic papers and articles by Josh Mitteldorf

In the neo-Darwinist paradigm (population genetics), fitness is equated with an incremental change in gene frequency from one generation to the next.  But some important traits cannot be explained in this way — major characteristics of the biosphere, including sex, aging, reproductive restraint, and the structure of heritability, which seems to be optimized for the sake of evolvability.  

What is missing in our concept of fitness is ecological stability.  All life is interdependent.  If a species is adapted only to maximize individual reproduction rates, it will quickly crash the ecosystem on which it depends.  I propose that ecological homeostasis is a major target of natural selection, rivaling reproductive fitness in strength, and generally opposing reproductive fitness when it becomes overextended.  Not just groups, but whole ecosystems are adapted for homeostasis.      (more*)

Menopause: Why animals continue to live when fertility has ended: (with Charles Goodnight) Many animals have evolved life plans that include a substantial post-reproductive period.  The standard explanation is that this has to do with caring for offspring and grandchildren; but post-reproductive life is not limited to animals that care for their young.  Worms and fish, for example, live past their fertility.  We propose that post-reproductive individuals buffer a population in times of stress, and help prevent extinctions.

Evolutionary Origin of Aging: (Book chapter appropriate for MDs and others with some biological expertise.)   Detailed story of how theoretical biases and a belief in Nature’s benevolence have caused evolutionary biologists to miss the truth about aging.  Evidence from genetics and experimental gerontology supports the view of aging as genetically-programmed self-destruction.   This is good news for anti-aging medicine, because it means that interventions are possible that target aging at the level of signaling rather than requiring invasive measures to repair damage.

Aging is not an Accumulation of Damage: Medical researchers commonly assume tat the reason for aging is that the body becomes damaged faster than it can repair itself, and eventually the repair mechanisms themselves become damaged.  Oxidative stress is invoked especially frequently.  This view is borrowed from vague ideas about thermodynamics, and it misses an essential characteristic of life: that it is able to create order within itself as it dumps entropy into the environment.  Evolutionary biologists have a different ideas about where aging comes from, and their view is far more hopeful for the long-term program of anti-aging medicine.

Female Fertility and Longevity:  A great deal of evolutionary theory is based on the notion that the body has to choose between high fertility and an adequate repair rate.  These theories all predict that having children should shorten a woman's life.  The data seems to show the opposite, however:  The more children a woman has (and the later in life she has them), the longer her life expectancy.

Senescence as an Adaptation to Limit the Spread of Disease: (with John Pepper) A popular explanation for the evolution of sex is that genetic diversity is valuable for its own sake, because pathogens are so finely tuned to attack a specific genotype, and because they mutate so rapidly.  In this paper, we adapt the theory to evolve senescence on a two-dimensional grid model.

Aging Selected for its Own Sake:  A wide body of experimental evidence makes pleiotropic theories of aging untenable.  In fact, the evidence indicates that aging has been selected for its own sake, and shaped affirmatively by natural selection.  This is a wake-up shock to evolutionary theory, and calls into question the definition of fitness that has been applied for most of the 20th century.  (Evol Ecol Res, Nov 2004)

Programmed and Altruistic Aging:  (with Valter Longo and Vladimir Skulachev Apoptosis in single-celled entities has no redeeming value to the individual, and must be regarded as an altruistic adaptation.  Detailed study of its occurrence suggests a role in regrowth when a colony is stressed.  (Nature Reviews Genetics, Oct 2005)

Demographic Homeostasis and the Evolution of Senescence: A mechanism by which aging can evolve as an adaptation, based on its contribution to damping population instabilities that lead to extinction.  (Evol Ecol Res, Mar 2006)
(another version presented at ALife 9 in Boston, 9/04.)

How evolutionary thinking influences our medical strategies for diseases of old age: If we think that nature has already 'done the best she can' by us, we come up with a very different approach than if we think that nature has programmed us to die.  (from SENS-2 conference, Cambridge, 9/05)

How can evolutionary theory accommodate recent empirical results on organismal senescence? (with John Pepper) Established theory asserts that aging has evolved because of the decline in the force of natural selection over an individual lifetime.  A fundamental prediction derived from this premise is that in nature, more 'dangerous' locations with higher extrinsic mortalities should evolve shorter life spans.  But this is not always the case. We document one spectacular exception, in which it is difficult to avoid the conclusion that faster aging has evolved to 'pick up the slack' when extrinsic mortality is low!  (Theory in Biosciences 126:3-8)

Is ecosystem homeostasis an adaptation? Thoughts on the foundations of the population genetic paradigm, derived from four general observations that are difficult to explain with models based on individual selection.  A model ecosystem that you can play with:  Source code (Delphi Pascal).  Windows app

Caloric Restriction and the Case for Aging as an Adaptation: The fact that the metabolism seems handily able to extend life under stress shows that it is "holding back" during normal times. This is at odds with prevailing theories of why senescence evolved.

How to Calculate Fitness from Life History Variables: What is the appropriate way to value the contributions to fitness from fertility and longevity? In this approach, we do for the Logistic Model what Fisher once did for exponentially expanding populations with the Euler-Lotka equation.  Acrobat PDF version

Population Viscosity and the Evolution of Altruism: (with David Wilson) A computer model of evolution on a grid, in which group selection emerges from simple rules about geometry and mobility. Acrobat PDF version
Source code for model (Borland Pascal)

Caloric Restriction and the Disposable Soma Theory: The most popular and successful evolutionary theory of aging is incompatible with the experimental fact that animals live longer the less they eat. Acrobat PDF download

Demographic Evidence and Evolutionary Theories of Aging: Two case studies make the case that sometimes demographers have bent over backward to find evidence of a tradeoff between fertility and longevity in their data.

Evolution of the Prudent Predator: Can animal populations self-regulate for the sake of demographic stability? A model of multilevel selection offers a plausible mechanism.

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