The Role of Extinction in Evolution Essay Example

later diversification by the survivors.

Simpson saw interspecies competition as only rarely the cause of extinction of species or larger groups.He thought replacement of one group by another was generally passive. In the history of life it is a striking fact that major changes in the taxonomic groups occupying various ecological positions do not, as a rule, result from direct competition of the groups concerned in each case and the survival of the fittest, as most students would assume a priori. On the contrary, the usual sequence is for one dominant group to die out, leaving the zone empty, before the other group becomes abundant. Read about evidence of evolutionIt is impossible to prove that there are no exceptions to this generalization so that there is some danger that it may represent the statement of an a priori postulate rather than evidence for the postulate; but I believe that this is a valid deduction from the facts.

--- When full diversity does return, it often has a strikingly different character. A classic example is the history of marine reefs. Reef communities have been wiped out several times in the past 600 million years, coinciding in four cases with Big Five events.Each time reefs reappear, the principal framework organisms have changed, switching back and forth between calcareous algae, sponges, bryozoans, rudist mollusks, and various corals.

The contemporary term "coral reef' describes only the current occupants of that adaptive zone. For a species to survive for several million years, as many do, it must be well adapted to the physical and biological stresses normal in its environment. Tree species,

for example, that can withstand, or even benefit from, forest fires have presumably evolved this ability because forest fires are common in their environment.It may well be that most species have evolved ways of surviving anything that their environment can throw at them, as long as the stress occurs frequently enough for natural selection to operate. This implies, in turn, that likely causes of extinction of successful species are to be found among stresses that are not experienced on time scales short enough for natural selection to act Extinction is evidently selective at certain times and places but the effects tend to be subtle and require careful analysis of large data bases.Darwin's contention that all extinction is selective cannot be sustained, although this may reflect only our inability to recognize complex patterns in an imperfect fossil record.

Despite of many uncertainties, we can formulate a reasonable statement of the probable role of extinction, containing the following elements. extinction of a widespread species requires an environmental shock and it must be applied rapidly enough to prevent adaptation by natural selection or escape by migration. Survivors are most likely to be those organisms which fortunately pre-adapted to an unexpected stress.Although the extinction does not make a creative contribution by itself, it may be decisive in sustaining or eliminating such structures. The major extinctions have a profound influence on the future: both constructive and destructive.

All things are being equal to one another, it's just that the species is not well adapted on surviving the environmental pressures. It is said to be an inevitable outcome. But there are some who dictates that extinction plays no direct role in

evolution, but generally, there is a role but the study carry out very weak.