This is to ignore the fact that many extinctions of species were caused not by "natural selection" but by evolutionarily random large-scale catastrophe. The disappearance of the dinosauria is a now generally accepted instance. Far more recent is the experience of the American continent, where perfectly adapted horses, camels, and elephants (but not bisons) were all wiped out.
Shane Mage
^^^^^^ CB: Mass extinctions are some of the main examples of natural selection. The _changes_ in the environment that create a whole new "field" of fitness are random,in that we can't predict them, as a comet falling ( I suppose now new ice age type environmental or global warming type environmental changes are being predicted by scientists).
How environmental changes make some species that used to be fit, unfit, and some new species fit, that didn't used to be "fit" or exist is random, but we retrospectively think that paleontologists can uncover some of the concrete relations between the traits of the different species in and the specific changes in the environment by which some species go extinct and some species arise.
Fitness is not a fixed and permanent status. Fitness is relative to the environment, and when the environment changes, as with an comet hitting the earth, there is a drastic, sudden change of fitness and unfitness status across many species, genera and families and orders of species.
In this fundamental dialectic of nature, of life and death, the extinctions' negations result in new species arising en masse in the negation of the negation.
In Stephen Jay Gould and Niles Eldrige theory of punctuated equilibrium, the mass extinctions are the main examples of punctuations. Many species go extinct, and many new species arise. Darwinism _par excellence_. Dinosaurs go out; Mammals come in. Gould sites several mass extinctions in _Ever Since Darwin_. Cambrian, _______, _______,.
The main "leaps" of evolution are natural selection in mass extinctions/mass speciations. These "periods" or "commas" ( as in punctuations) are long in absolute terms, but short in relative terms of all natural historical scales. So, they are leaps, punctuations. Just as a period or comma is a relatively short part of the total length of a sentence, the extinctions/mass extinctions are relatively short in overall natural historical epochs.
They occur in leaps and so the famous gaps in the fossil record that were a contradiction to Darwin's gradualist, not fully dialectical, evolutionism. Evolutionism is actually evolutionism/revolutionism. Mass extinctions are examples of big revolutions in natural history.
Only death is immortal.
^^^^^^^
http://en.wikipedia.org/wiki/Extinction_event
Extinction events
The classical "Big Five" mass extinctions identified by Raup and Sepkoski (1982) are widely agreed upon as some of the most significant: End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous.
These and a selection of other extinction events are highlighted below:
488 million years ago - a series of mass extinctions at the Cambrian-Ordovician transition (the Cambrian-Ordovician extinction events) eliminated many brachiopods and conodonts and severely reduced the number of trilobite species. 444 million years ago - at the Ordovician-Silurian transition two Ordovician-Silurian extinction events occurred, probably as the result of a period of glaciation. Marine habitats changed drastically as sea levels decreased, causing the first die-off, then another occurred between 500 thousand to a million years later when sea levels rose rapidly. It has been suggested that a gamma ray burst may have triggered this extinction. [1] 360 million years ago - near the Devonian-Carboniferous transition (the Late Devonian extinction) a prolonged series of extinctions led to the elimination of about 70% of all species. This was not a sudden event, with the period of decline lasting perhaps as long as 20 million years. However, there is evidence for a series of extinction pulses within this period. 251 million years ago - at the Permian-Triassic transition (the Permian-Triassic extinction event) about 95% of all marine species went extinct. This catastrophe was Earth's worst mass extinction, killing 53% of marine families, 84% of marine genera, and an estimated 70% of land species (including plants, insects, and vertebrate animals.) 200 million years ago - at the Triassic-Jurassic transition (the Triassic-Jurassic extinction event) about 20% of all marine families as well as most non-dinosaurian archosaurs, most therapsids, and the last of the large amphibians were eliminated. 65 million years ago - at the Cretaceous-Paleogene transition (the Cretaceous-Tertiary extinction event) about 50% of all species became extinct (including all non-avian dinosaurs). This extinction is widely believed to have resulted from an asteroid or comet impact event. Present day - the Holocene extinction event. A 1998 survey by the American Museum of Natural History found that 70% of biologists view the present era as part of a mass extinction event. Some, such as E. O. Wilson of Harvard University, predict that man's destruction of the biosphere could cause the extinction of one-half of all species in the next 100 years. Research and conservation efforts, such as the IUCN's annual "Red List" of threatened species, all point to an ongoing period of enhanced extinction, though some offer much lower rates and hence longer time scales before the onset of catastrophic damage. The extinction of many megafauna near the end of the most recent ice age is also sometimes considered a part of the Holocene extinction event.
Cretaceous-Tertiary extinction event
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The Cretaceous-Tertiary (K-T or KT) extinction event, also known as the KT
boundary, was a period of massive extinction of species, about 65.5 million
years ago. It corresponds to the end of the Cretaceous Period and the
beginning of the Tertiary Period. (K is the traditional abbreviation for the
Cretaceous period. Cretaceous comes from the Latin for chalk, creta. The K
comes from the German word for chalk kreide, or possibly Greek kreta. The K
is used so as to avoid confusion with the Carboniferous period which uses
the letter C.)
Badlands near Drumheller, Alberta where erosion has exposed the KT boundary.The duration of this extinction event (like others) is unknown. Many forms of life perished (embracing approximately 50% of all genera), the most often mentioned among them being the non-avian dinosaurs. Many explanations for this event have been proposed, the most widely-accepted being the results of an impact on the Earth of an object from space.