INTRODUCTIONMEANING OF EXTINCTION AND BIOLOGICAL EVOLUTION

TYPES OF EXTINCTION CAUSES OF EXTINCTION

MAIN BODY“INFLUENCE OF EXTINCTION ON BIOLOGICAL

EVOLUTION”

CONCLUSION REFERENCES

MEANING OF EXTINCTION

• Extinction is a state of ceasing to be; destruction; suppression.

• Specifically; it is the ceasing to exist of a species of living organism, such as a plant or animal, whose numbers declined to the point where the last member of the species died and therefore no new members of the species could ever again be born.

MEANING OF BIOLOGICAL EVOLUTIONBiological evolution is defined as the change in the gene

frequency within a gene pool of a given population from one generation to the other.

• TYPES OF EXTINCTION1. Co extinction

• The loss of one species leads to the loss of another in a chain effect. A small impact in the beginning of an extinction can have an overall larger effect. Reasons for co extinction could be as a result of a predator losing its food source or if a key species becomes extinct and the ecosystem becomes off balance.

For example, the decline in the red ant Myrmica

sabuleti in southern England caused by habitat loss, resulted in the local extinction of the Large Blue butterfly, which is dependent on the ant as a host for the larvae .

2. Mass Extinction • Is an extinction event that destroys many

species at once • A sharp decrease in the number of species

on Earth in a short period of time • Coincides with a sharp drop in speciation • The process by which new biological species

arise • There have been at least 5 mass extinction

events with the mosts recent being 65 million years ago with the dinosaur extinction

• For example, the ostracoderms, which appeared in the Cambrian Period, about 510 million years ago, and became extinct at the end of the Devonian,

3. Planned Extinction • Human controlled extinctions were

thought to be helpful for the human population but generally ended in the spread of deadly viruses.Examples:

• Smallpox- extinct in the wild • Polio- nearly extinct but can be found

in some parts of the world

CAUSES OF EXTINCTION1. Habitat degradation• is currently the main anthropogenic cause

of species extinctions. The main cause of habitat degradation worldwide is agriculture, with urban sprawl, logging, mining and some fishing practices close behind. The degradation of a species' habitat may alter the fitness landscape to such an extent that the species is no longer able to survive and becomes extinct. This may occur by direct effects, such as the environment becoming toxic, or indirectly, by limiting a species' ability to compete effectively for diminished resources or against new competitor species.

• Habitat degradation through toxicity can kill off a species very rapidly, by killing all living members through contamination or sterilizing them. It can also occur over longer periods at lower toxicity levels by affecting life span, reproductive capacity, or competitiveness.

• Habitat degradation can also take the form of a physical destruction of niche habitats. For example; the widespread destruction of tropical rainforests and replacement with open pastureland. Destruction of the dense forest eliminated the infrastructure needed by many species to survive. For example, a fern that depends on dense shade for protection from direct sunlight can no longer survive without forest to shelter it.

2. Predation, competition, and disease

• Recently in geologic time, Humans have been transporting animals and plants from one part of the world to another for thousands of years, sometimes deliberately and sometimes accidentally. In most cases, such introductions are unsuccessful, but when they do become established as an invasive alien species the consequences can be catastrophic. Invasive alien species can affect native species directly by eating them, competing with them, and introducing pathogens or parasites that sicken or kill them or, indirectly, by destroying or degrading their habitat.

3. Genetic pollution• Purebred wild species evolved to a specific ecology can

be threatened with extinction through the process of genetic pollution—i.e., uncontrolled hybridization introgression genetic swamping which leads to homogenization or out-competition from the introduced. Endemic populations can face such extinctions when new populations are imported or selective bred by people, or when habitat modification brings previously isolated species into contact Extinction is likeliest for rare species coming into contact with more abundant ones; interbreeding can swamp the rarer gene pool and create hybrids, depleting the purebred gene pool.

• The gene pool of a species or a population is the variety of genetic information in its living members. A large gene pool (extensive genetic diversity) is associated with robust populations that can survive bouts of intense selection. Meanwhile, low genetic diversity reduces the range of adaptations possible. Replacing native with alien genes narrows genetic diversity within the original population, thereby increasing the chance of extinction.

4. Climatic changesThis has many causes and has a big effect on extinction. The biodiverse earth can not keep up with the rapid changes in temperature and climate. The species are not used to severe weather conditions and number of long seasons or a changing chemical make up of their surroundings. As more species die it is only making it difficult for the survivors to find food. The warm climates we are used to present day are perfect for diseases and epidemics to thrive.

INFLUENCE OF EXTINCTION ON EVOLUTION

• 1. Elimination of unfavorable genes i.e. gene degradation from the gene pool which goes gradually

• 2. Introduction of new species with more favorable genes to adapt to the habitat. Example: extinction of dinosaurs which created room for mammals and reptiles to colonize the habitat.

• Another example is the extiction of archeopteryx – a bird like reptile, which gave room for bird to colonise the habitat

Charles Darwin on Extinction

In the Origin (1), Darwin made his view of extinction, and its role in evolution, quite clear. He saw four essential features:

(i) Extinctions of species have occurred gradually and continuously throughout the history of life.

... species and groups of species gradually disappear, one after another, first from one spot, then from another, and finally from the world.

• ... the complete extinction of the species or a group is generally a slower process than their production.

• ii) Sudden disappearances of many species, now called mass extinctions, did not actually occur. Darwin was convinced that sudden disappearances of species from the fossil record were due solely to unrecognized gaps in the temporal record.

• With respect to the apparently sudden extermination of whole families or orders, as of Trilobites at the close of the palaeozoic period [Permian mass extinction] and of Ammonites at the close of the secondary period [K-T mass extinction], is probably due to wide intervals of time between our consecutive formations

iii. Species extinction is usually, though not always, caused by the failure of a species in competition with other species. That is, causes of extinction are generally biological, not physical.....

• each new variety, and ultimately each new species, is produced and maintained by having some advantage over those with which it comes into competition; and the consequent extinction of the less-favoured forms almost inevitably follows.

• iv.The extinction of species is closely tied to the process of natural selection and is thus a major component of progressive evolution. In some passages of the Origin, Darwin seems to have seen extinction as part of natural selection; in others, as an inevitable outcome. Darwin listed the fundamental components of the

evolutionary process: reproduction, inheritance, variability, struggle for life, and natural selection, with its "consequences"

divergence of character and the extinction of less improved forms.

• CONCLUSION

Extinctions have occurred many times throughout the history of life on Earth, and abundant evidence of the prior existence of animals and plants are found as fossils in rock formations many millions of years old.

It is believed by some that due to the influence of man on the environment and destruction of habitat, the rate of extinction of species is now higher than at any previous time on the earth.

CONCLUSION cont….

• Whatever may be the cause and type of extinction, extinction associated with natural selection as seen above, has a great influence in biological evolution.

REFERENCES.http://en.wikipedia.org/wiki/extinction

retrieved on 10/01/2011

http://en.wiktionary.org/wiki/extinction retrieved date 10/01/2011

http://www.uwec.ed/jolhn/eH4/extinction.htm retrieved on 10/11/2011

Raven, P & Johnson, G. (1986). Biology. Times mirror. Mosby college publishing.Toronto