Monday, May 30, 2011
[are they evolving or not?]
One popular version of evolution is punctuated equilibrium.
Punctuated equilibrium (also called punctuated equilibria) is a theory in evolutionary biology which proposes that most sexually reproducing species will exhibit little evolutionary change for most of their geological history, remaining in an extended state called stasis. When evolutionary change occurs, the theory proposes that it is localized in rare and rapid events of branching speciation.
This theory was proposed by paleontologists Niles Eldredge and Stephen Jay Gould, basically as a way of explaining why the fossils seem to indicate catastrophism, or sudden changes, not evolution, or gradual change.
The theoretical mechanism behind punctuated equilibrium is geographic speciation: that species with large central populations are stabilized by their large volume and the process gene flow. New and even beneficial mutations are diluted by the population's large size and are unable to reach fixation, due to such factors as constantly changing environments. If this is the case, then the transformation of whole lineages should be rare, as the fossil record indicates. Smaller populations on the other hand, which are isolated from the parental stock, are decoupled from the homogenizing effects of gene flow. In addition, pressure from natural selection is especially intense, as peripheral isolated populations exist at the outer edges of ecological tolerance. If most evolution happens in these rare instances of geographic speciation then evidence of gradual evolution should be rare.
One immediately apparent problem with this theory, is that actually, genetically isolated populations tend to degenerate rather than improve.
The Amish, for example, suffer from higher incidences of particular genetic disorders, including dwarfism (Ellis-van Creveld syndrome) and various metabolic disorders because almost all Amish descend from about 200 18th century founders.
Likewise, in Appalachia, inbreeding in isolated communities, particularly prior to the advent of the railroad, apparently lowered intelligence.
This seems to refute the entire basis for punctuated equilibrium - rather than evolve, genetically isolated and inbred populations get sick.
Posted by jewish philosopher at 11:19 AM