Scientific Issues and Problems with Traditional Evolution
Darwin's idea that current species are descended from different earlier species is now overwhelmingly confirmed by steadily increasing observational evidence and no longer has scientific opposition. Darwin's evolutionary mechanics theory, essentially survival of the fittest or natural selection, also fits the vast majority of observations. His idea was that mutational changes occasionally occurred in individual organisms. Sometimes the changes were inheritable. Sometimes inheritable changes improved the ability of individual organisms possessing them to survive longer (and thereby reproduce more) or to otherwise reproduce more, thus propagating their altered design in a population. According to traditional mechanics theory, any evolved organism characteristic must therefore improve the ability of individual organisms to live longer or reproduce more.
However, the traditional evolutionary mechanics theory, now known as neo-Darwinism or The Modern Synthesis, conflicts with some observations as described below. Because such a large proportion of observations conform, Darwin and many subsequent theorists assumed that conforming explanations for the relatively few conflicts would eventually be found. As time passed that did not happen and additional issues and conflicts surfaced leading to development of the alternative evolutionary mechanics theories beginning in 1962. Principal areas of conflict are listed below. This issue is absolutely critical to theories of biological aging (and gerontology) because such theories are dictated by evolutionary mechanics theory.
The extreme variation in life spans between similar species was immediately noted as a conflict following publication of Origin. If species were designed by the evolution process to have a species-specific life span, a design that purposely limited life span (programmed aging or programmed death), that observation conflicted with traditional "survival of the fittest" mechanics. If not, why did similar species have such different life spans? Wouldn't evolution be pushing for ever increasing life span such that species (at least similar species) would all have the same life span. If fundamental natural forces (that could not be overcome by evolution) limited life span, would they not apply equally at least to similar species? It is true, as many people note, that a life span that extended substantially beyond the age at which an organism lost the ability to reproduce would not create benefit because the evolutionary benefit of living longer results from reproduction. However, an organism that was designed to stop reproducing at a certain age would have the same problems with traditional theory as one that was designed to die at a certain age. Most researchers now think of age-related reproductive limitations as symptoms of aging rather than evolutionary causes of aging. Programmed aging theories (based on alternative mechanics) generally provide a better fit for observations and therefore add to support for alternative mechanics theories.
A few organisms have been observed that apparently do not age. They do not display deterioration in their survival traits (such as strength, mobility, or sensory capability) or any lessening of their reproductive capability with age. (See Negligible Senescence.) This is a problem for aging theories (based on traditional mechanics) that say aging results from fundamental limitations or is an unavoidable side-effect of some necessary function.
Various plants and animals were observed to die suddenly following reproduction. Semelparous organisms die following their first reproduction and include a mammal, the male marsupial mouse, which dies following mating. Salmon and octopus have similar behavior. Biological suicide represented a more explicit violation of traditional mechanics theory. There was no way to blame this behavior on fundamental processes causing gradual deterioration. A traditional explanation is that suicidal species trade suicide for increased reproductive capability. In some cases, such as octopus, no plausible traditional tradeoff has been identified.
Darwin responded regarding the above conflicts that there must be some hidden compensating benefit that offset the adverse nature of a design-limited life span. He did not specify the benefit. Theorists have been looking for and arguing about the compensating benefits ever since.
Biologists noted that some animals had behavior patterns leading them to protect unrelated members of their species at the expense of personal risk. According to traditional mechanics an animal should only defend itself, its mate, and its direct descendents in order to best propagate its personal design so this behavior conflicted. This is the "dog eat dog" or "red of tooth and claw" aspect of traditional mechanics theory, which says that each organism is out for itself and its immediate family and in competition with others. For some reason animal altruism, an obscure behavior of wild animals, has historically attracted more interest than the other seemingly more significant discrepancies.
Delayed Sexual Maturity
Many animals, especially males, have sexual maturity that occurs at a late age relative to what appears to be biologically necessary from a functional, growth or development perspective, a reproductive disadvantage. In animals that nurture or protect their young, this could result in compatible compensating benefit to direct descendents because older animals would be more able to perform those functions. In animals that do not nurture or protect young (e.g. reptiles), purposely late male sexual maturity appears to conflict with traditional theory.
Inheritance Mechanism Issues
Inheritance mechanisms are critical to any evolutionary mechanics theory because mutational changes occur in a single individual and then propagate into a population by means of biological inheritance. Darwin knew virtually nothing about the mechanics of inheritance. It was reasonable for him to assume that all mutations were equally likely, that the inheritance mechanisms of all species treated all mutations equally, and that therefore natural selection was the only process that differentially affected the propagation of mutations. Mutations occurred. Natural selection differentially affected their propagation. End of story. It was simple, elegant, intuitive, and appealing. As so often happens in science, especially biology, reality turned out to be much more complicated and messy.
During the intervening 150 years, genetics science has exposed more and more complexity in inheritance mechanisms. It is now clear that all of the above assumptions are incorrect. Some types of mutations have drastically more probability of occurrence than others. Inheritance mechanisms of different species handle mutations in different ways that clearly differentially affect propagation of mutational changes (see next section). It is increasingly clear that, in addition to natural selection, other processes are active and interact with natural selection in determining the path of evolution. These processes operate on even longer time frames than natural selection.
Two of the three categories of alternate mechanics theories (evolvability and gene-oriented mechanics theories) specifically propose that these discoveries support alternative theories. See How Genetics Discoveries Affect Evolution Theory and Digital Genetics.
Sexual reproduction represents a major conflict with traditional theory. First, according to traditional theory, the evolutionary goal of every organism is to propagate its own design. Organisms that reproduce asexually essentially clone their designs in their descendents and thus accomplish this function. However, in sexual reproduction an organism can not be sure that its descendents will express the individual organism's design since it is sharing control with the other parent. Additionally, because of the mechanics of sexual reproduction (e.g.. recessive characteristics), a descendent might not resemble either parent. Therefore sexual reproduction, represents a major step backward in accomplishing the traditional goal. Despite this, sexually reproducing species evolved from asexually reproducing organisms. Many current organisms including plants and some animals can reproduce both sexually and asexually. Note that behaviors and other fine details of a sexually reproducing organism's design dramatically affect its ability to achieve the traditional goal. An organism that had a behavior that caused it to seek mates that were as similar to itself as possible (e.g. close relatives) would produce descendents that were more like itself than one that had a mating behavior that caused it to seek mates that were different from itself (e.g. not close relatives). This is an example of an evolved organism design trait that affects its ability to propagate its design!
Second, traditional theory holds that evolution is driven by expressed phenotypic differences that create a performance difference, that is, a difference in the ability of individual organisms to survive and/or reproduce. The development of sexual reproduction required the development of multiple complex internal mechanisms such as those associated with meiosis. These mechanisms do not have any apparent positive effect on performance. As noted above the same organism could have been produced asexually. What then drove the evolution of the complex mechanisms associated with sexual reproduction?
Third, sexual reproduction is massively reproductively adverse relative to asexual reproduction. Only females can bear young (instead of all the organisms), and reproduction requires the additional effort of finding a mate and mating. If the animal finds itself in an area in which members of the opposite sex of its species do not exist, it cannot reproduce. If it dies before finding a mate, it cannot reproduce.
Theorists have been arguing for 150 years as to the origin and purpose of sexual reproduction. What benefit does sexual reproduction confer that could possibly compensate for the massive disadvantages. One of the alternatives to traditional theory, evolvability, suggests that sexual reproduction aids the evolution process by increasing local variation. Sexually reproducing organisms were therefore able to evolve (adapt) more rapidly producing the compensating benefit. Many features of sexual reproduction seem to be more or less obviously designed to increase variation. The mechanism that causes chromosome shuffling during meiosis delivers 16.7 million possible combinations of inherited genetic characteristics resulting from shuffling each human parent's chromosomes. Apparently this was not sufficient and nature developed an unequal crossover mechanism that shuffles genetic data within a chromosome!
Traditional theory assumes that all organisms possess the capacity for further evolution and that this capacity is a constant that does not vary between populations or species. There is growing evidence (much from recent genetics science) that this is not true leading to evolvability theories of evolutionary mechanics. If the ability of an organism to evolve can itself be affected by evolved design characteristics, then any valid evolutionary mechanics theory must explain why and how that situation affects or does not affect the evolution process. Proponents of traditional theory have not responded to this problem.
Science Schism Regarding Evolutionary Mechanics
The observations described above have resulted in a schism in the bioscience community regarding evolutionary mechanics. Some theorists still loudly insist on the validity of traditional mechanics (specifically excluding even the possibility of secondary natural effects influencing the evolution process) and contend that the relatively small number of conflicting observations can eventually be explained within that framework. Non-programmed theories of aging are part of this effort.
The other faction believes that the combined net effect of all of the apparently conflicting observations demands at least some adjustment to traditional mechanics and has produced proposed alternative mechanics theories including dependent theories of aging (the programmed theories). Needless to say, both factions cannot be simultaneously correct. Major efforts by the second faction began only relatively recently (1962, following publication of most of the major non-programmed aging theories). Recent trends have been toward more observational evidence that conflicts with traditional mechanics and supports alternatives. However, there is no current consensus among the alternative faction as to which or which combination of alternative theories is correct.
Alternative Evolutionary Mechanics Theories
None of the alternatives suggest that survival of the fittest (natural selection, individual fitness) is not the most important factor directing the evolution process, rather they suggest that other natural factors also participate in the process. There are explanations based on alternative theories for all of the apparent discrepancies. The different categories of alternative theories are listed below.
Group Selection Theories Including Kin Selection A group benefit can offset an individual disadvantage.
Evolvability Theories A benefit to the evolution process can offset an individual disadvantage.
Gene-Centered Theories A benefit to propagation of genes can offset an individual disadvantage.
Genetics and Evolutionary Mechanics Why genetics discoveries support alternative mechanics theories.
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