Theory Of EvolutionTheory Of EvolutionWhat is evolution?What is evolution?

The Origin Of SpeciesThe Origin Of Species

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

A Process Of Continuous A Process Of Continuous ChangeChange

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

The The FossilFossil Record Record

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

Geographic Distribution Of Geographic Distribution Of Related SpeciesRelated Species

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

Pre-Darwinian TheoriesPre-Darwinian Theories

Carolus LinneousCarolus Linneous

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

Jean Baptiste De Monet , Jean Baptiste De Monet , Chevalier De LamarckChevalier De Lamarck

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

George CuvierGeorge Cuvier A French scientist, George Cuvier(1769-1832), A French scientist, George Cuvier(1769-1832),

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

CharlesCharles

DarwinDarwin

Darwin had observed the wide variety Darwin had observed the wide variety of finches and the unusual types of of finches and the unusual types of tortoises and iguanas, found on the tortoises and iguanas, found on the Galapagos islands. He also had a Galapagos islands. He also had a knowledge of comparative anatomy knowledge of comparative anatomy and an understanding of previously and an understanding of previously circulating theories of evolution, which circulating theories of evolution, which were suggestive but flawed. It was were suggestive but flawed. It was from these elements that Darwin from these elements that Darwin created his powerful new synthesis.created his powerful new synthesis.

According to Darwin’s theory, initially slight According to Darwin’s theory, initially slight variations in populations of organisms may give variations in populations of organisms may give certain individuals an advantage in adapting to certain individuals an advantage in adapting to their environment. Any such advantage may be their environment. Any such advantage may be passed on from parents to offsprings, causing the passed on from parents to offsprings, causing the advantageous traits to proliferate in subsequent advantageous traits to proliferate in subsequent generations. Meanwhile, the subsequent generations. Meanwhile, the subsequent generations of organisms may eventually come generations of organisms may eventually come from their own species. Species are caused by from their own species. Species are caused by the struggle for existence in specific the struggle for existence in specific environmental conditions. For example, it’s clear environmental conditions. For example, it’s clear that Bengal tigers, Siberian tigers and African that Bengal tigers, Siberian tigers and African lions are probably descended from the same lions are probably descended from the same predecessor, but they now belong to different predecessor, but they now belong to different species of the genus felis.species of the genus felis.

This work has been produced by:This work has been produced by:

Rosa ScanniffioRosa Scanniffio

Flavia NdriollariFlavia Ndriollari

Orsolinda PerrucciOrsolinda Perrucci

Rosanna LopedotaRosanna Lopedota