Theory Of Evolution

1. Theory Of Evolution What is evolution?

2. The OriginOfSpecies The tumult in the middle of the 19° century was accompanied by the publication of Darwin’s Origin of species. The principal topic of this work was that the life forms we see today are the result of millions of years of evolution by a process Darwin called “natural selection”. The work had a revolutionary impact on Western thought which has still not been fully assimilated.

3. A Process Of Continuous Change Biological evolution is a genetic change in a population from one generation to another. The speed and direction of change is variable with different species lines and at different times. Continuous evolution over many generations can result in the development of new varieties and species. Likewise, failure to evolve in response to environmental changes can, and often does, lead to extinction. All life forms, including people, evolved from earlier species. Furthermore, all still living species of organisms continue to evolve today.

4. The Fossil Record The remains of animals and plants found in sedimentary deposits provide a record of past changes through time. The existence of fossils confirms that species are not fixed but can evolve into other species over time. The evidence also shows that what has appeared to be gaps in the fossil record is due to incomplete specific species lines. The most of these so-called “missing links in the chain of evolution” are filled with transitional fossil specimens.

5. Geographic Distribution Of Related Species Another clue of evolution is found in the natural geographic distribution of related species. It is clear that major isolated land areas and island groups often evolved their own distinct plant and animal communities. For instance, before humans arrived 60-40000 years ago, Australia had more than 100 species of kangaroos, koalas and other marsupials but didn’t have none of the most advanced terrestrial placental mammals such as dogs, cats, bears, horses. Land mammals were entirely absent from the isolated island that make up Hawaii and New Zealand. Each of these places had a great number of plant, insect and bird species that were found nowhere else in the world. The most likely explanation for the existence of Australia’s, New Zealand’s, and Hawaii’s biotic environments is that the life forms in these areas have been evolving in isolation from the rest of the world for millions of years.

6. Pre-DarwinianTheories

7. Carolus Linneous The Swedish botanist Karl von Linné(1707-1778) was the first class scientist. His most important contribution to science was is logical classification system for all living beings he proposed in is book “SystemaNaturae”(1735). He described plants and animals on the basis of physical appearance and classified them relatively to each other according to the degree of their similarities. He used a binomial nomenclature in naming them. Organisms were given two Latin names: genus (usually written with a capital letter) and species. Each genus could have many related species and it was also part of larger categories of living beings.

8. Jean Baptiste De Monet , Chevalier De Lamarck The first evolutionistwho started his ideas about the processes leading by the logical change was a French aristocrat, J. B. Lamarck( 1744-1829). Unfortunately, his theory about these processes was incorrect. Lamarck believed that microscopic organisms appeared spontaneously from inanimate materials and than evolved gradually and progressively into more complex forms through a constant tension to the perfection. Lamarck thought that humans were the ultimate product of this evolution. He believed that evolution was mostly due to the inheritance of acquired characteristics as creatures adapted to their environments. He thought that giraffes evolved their long necks by each generation stretching further to get leaves in trees and that this change in body shape was then inherited. Lamarck also believed that creatures could develop new organs or change the structure and function of old ones as a result of their use or disuse.

9. George Cuvier A French scientist, George Cuvier(1769-1832), discredited Lamarck’s theory. Cuvier did not reject the idea that there had been earlier life forms. He was the first scientist to describe extinctions of ancient animals. However, he rejected the idea that their existence implied that evolution had occurred: he maintained the “fixity” of species. Cuvier advocated the theory of catastrophism. This held that there have been violent and sudden natural catastrophes such as great floods and the rapid formation of major mountain chains. Plants and animals living in those parts of the world where such events occurred, were often killed off according to Cuvier. Then new life forms moved in from other areas. As a result, the fossil record for a region show, abrupt changes in species.

10. Charles Darwin

11. Darwin hadobserved the wide varietyoffinches and the unusualtypesoftortoises and iguanas, found on the Galapagos islands. Healsohad a knowledgeof comparative anatomy and anunderstandingofpreviouslycirculatingtheoriesofevolution, whichwere suggestive butflawed. Itwasfromtheseelementsthat Darwin createdhispowerfulnewsynthesis.

12. Accordingto Darwin’s theory, initiallyslightvariations in populationsoforganismsmaygivecertainindividualsanadvantage in adaptingtotheirenvironment. Anysuchadvantagemaybepassed on fromparentstooffsprings, causing the advantageoustraitsto proliferate in subsequentgenerations. Meanwhile, the subsequentgenerationsoforganismsmayeventually come fromtheirownspecies. Species are causedby the struggleforexistence in specificenvironmentalconditions. Forexample, it’s clearthatBengaltigers, Siberiantigers and Africanlions are probablydescendedfrom the samepredecessor, buttheynowbelongtodifferentspeciesof the genusfelis.

13. This work hasbeenproducedby: Rosa Scanniffio Flavia Ndriollari OrsolindaPerrucci Rosanna Lopedota