Igor233

Unresolved Issues with the Evolution Process

(Proposed addition to the Evolution page submitted May 17, 2009) (See also User:Igor233/Evolution issues, evolution issues User:Igor233/sandbox.)

Although the vast majority of observed organism characteristics conform to the natural selection theory there are some apparent conflicts. The very wide variation in life spans between even very similar species led to the conclusion that life span was being substantially internally self-limited by the particular design of the organism, a violation of the natural selection concept. Semelparous species and others that die suddenly following reproduction appeared to be more explicit examples of self-limited life span. Darwin suggested in later editions of Origin that these observations could be explained by the existence of some undiscovered compensating benefit associated with the adverse life span limitation.

Subsequent theorists, primarily based on data acquired prior to 1950, (See Neo-Darwinism or modern evolutionary synthesis) held that evolutionary propagation and retention of organism mutational changes could only occur if the change resulted in benefit to the ability of individual organisms (including immediate descendents) to survive or reproduce. They held that any compensating benefit must fit this rule. Peter Medawar (1952) and others subsequently proposed various theories of gradual mammal aging that were compatible with the individual benefit concept but did not address semelparous organisms.

Other apparent conflicts eventually surfaced. Altruism involves observation of animal behaviors that apparently violate the individual benefit rule (e.g. an animal risking its own life protecting an unrelated member of its species). Sexual reproduction, because of the relative reproductive uselessness of males and other factors also appears to represent an individual disadvantage relative to asexual reproduction and yet was evolved and retained. Organism characteristics that seem to self-limit reproduction without compensating individual benefit also appeared. These include mating rituals that act to generally delay mating, and apparently unnecessarily late age of puberty in some species.

Beginning in 1962 a formal scientific disagreement has existed regarding the definition of evolutionary benefit. Various group selection theories (including kin selection and multilevel selection) were developed contending that benefit to groups (beyond immediate descendents) can compensate for individual disadvantage and thus allow evolution and retention of an organism characteristic that produces a net individual disadvantage. Corresponding theories regarding the group benefits of conflicting observations including altruism, aging as a self-limitation[3], etc. then appeared. Neo-Darwinists continue to contend that group selection is impossible because of propagation issues and propose their own explanations for the apparent conflicts.

Other theorists (primarily since 1995) contend that characteristics that benefit the ability of an organism to evolve (increase evolvability) can also evolve and be retained despite having a net individual disadvantage. Corresponding evolvability theories of aging[4] (see Evolution of ageing) and other apparently individually adverse characteristics appeared. Neo-Darwinists reject evolvability as a form of group selection.

Generally, neo-Darwinism (or modern synthesis) provides a simpler and more plausible propagation scheme and benefits from the conformance of the great majority of observations as well as long tradition. Group selection and evolvability provide better matches to the minority of non-conforming observations but suffer from less developed propagation concepts. In one form or another this issue has persisted for 150 years and no scientific agreement is expected in the near-term.

The Selfish Gene theory is another attempt to explain some apparently individually adverse observations, primarily altruism, and has issues similar to those of group selection.

The process of biological inheritance is central to the propagation of mutational changes in evolution. A consequent issue concerns the degree to which relatively recent (1950 to present) discoveries regarding the process of inheritance in sexually reproducing species (see genetics) should affect thinking about the evolution process. Many aspects of the genetic design of a complex organism (such as the particular location (locus) of a gene on a chromosome, introns, transposons, and junk DNA) are thought to have no effect on the organism's phenotype and therefore nominally do not result in or affect an evolvable (selectable) property under classical theory. However, all of these aspects, through genetic linkage and other mechanisms plausibly affect the inheritance process and thereby potentially affect the evolution process. For example, the concept of mutational robustness suggests that characteristics having identical phenotypic effect could vary in their susceptibility to mutational alteration by virtue of their particular underlying genetic design thus affecting the evolution process. This sort of analysis suggests that classical propagation models may be inadequate, especially regarding sexually reproducing species, and increases the plausibility of group selection and other concepts that violate classical theory.

External links

• Evolutionary Theories of Aging and Longevity
• The Evolutionary Theory of Aging by João Pedro de Magalhães.
• Programmed-Aging.Org Site provides comprehensive information on programmed ageing, the programmed/non-programmed controversy, and underlying evolution controversies.
• How Evolutionary Thinking Affects People's Ideas About Aging Interventions
• AnAge Animal Ageing and Longevity Database Provides maximum observed ages and sexual maturity ages for many animals.
• The Case for Programmed Mammal Aging Describes empirical data, evolutionary rationale, and historical perspective supporting programmed ageing in mammals.
• Life Table for USA 2005 Probability of death as a function of age

References

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