EvolutionStolen from Tina RiouxBy Mike Chapman
EvolutionThe theory that species change over time; it is process of change that produces new species from pre-existing species.
Evolution is an important scientific concept because it attempts to explain why living organisms, so similar in their biochemistry and molecular biology, are so different in form and function.
EvolutionSTART OF THE EVOLUTIONARY THEORYThe world during the mid-eighteenth century was quite different from the world we know today. The religious belief that every type of organism had been separately created influenced many biologists.
Many tried to explain the diversity and complexity of all the living things but none formulated a definite theory. None could present enough supportive data to suggest a general mechanism by which evolution might occur.
EvolutionJean Baptiste de Lamarck
The first coherent theory of evolution was proposed by Lamarck (1744-1829), the French naturalist, in 1809. He stated clearly that more complex organisms were descended from less complex organisms and went on to suggest that this demonstrated a built-in drive towards perfection. In those days it was believed that humans represented perfection, and that all organisms were on their way to achieving this perfect state.
In order to account for the constant presence of simple and less complex organisms, he suggested that spontaneous generation was always producing a fresh supply of less complex organisms.
Lamarck also believed that plants and animals became adapted to their environment. He stressed that it was the environment that caused the certain changes to occur. He proposed 3 basic theories:
1) The Theory of Need - If an organism needed a structure, it developed one and the next generation would inherit it.
2) Theory of Use and Disuse If you need and used a structure regularly, you would keep it, however if the structure was not used the next generation would lose it.
Evolution3) Inheritance of Acquired Characteristics The example he used here was that the long neck of the giraffe developed over time because generations of these animals kept stretching their necks to reach food up high in the trees. It also meant that if a structure was missing or lost, the offspring would also be without it.
Charles Darwin and Alfred WallaceCharles Darwin (1809-1882), the name most widely known when evolution is mentioned, formulated his ideas from visiting the Galapagos Islands, New Zealand, Australia, and Madagascar. Traveling abroad the H.M.S. Beagle as a naturalist, he observed many different animals and plants and noted the changes that had taken place within similar types of species. Wallace, on the other hand, was coming to the same conclusions as Darwin but did so by observing organisms within Europe.
EvolutionAfter Darwins return from his travels, Wallace sent Darwin a letter that contained his theory on why organisms change and adapt to their environment. Both scientists presented their conclusions at the Linnaean Society of London in 1858, but it was Darwin that later presented detailed evidence in support of his theory of evolution. To the left is Charles Darwin and to the right is Alfred Wallace.
EvolutionCharles described his experiments and reasonings at great length in his famous book entitled, On the Origin of the Species. Darwins proposed mechanism of evolution is called natural selection and may be summarized as follows:
Overproduction In a population, there are many more individuals produced each generation than can survive and reproduce.
Struggle for Existence (Competition) Due to overproduction, organisms must compete for limited resources (food, water and habitat).
Variation (Change by Chance) - No two individuals are exactly alike. These differences in traits were believed to be passed on to offspring by parents. Darwin did not understand what caused these variations among different organisms.
EvolutionSurvival of the Fittest (Natural Selection) Individuals with adaptive characteristics are more likely to successfully reproduce than are those with other characteristics. This is where the saying, Only the strong survive can be used.
Origin of New Species(Speciation) As generations pass, new species arise from the accumulation of inherited variations. When an organism appears that is much different than the orginal organism, it becomes a new species.
EvolutionHugo De VriesDe Vries (1848-1935) proposed what is called the Modern Synthesis Theory. His theory stated, with the discovery of DNA, that genetic mutations, not chance were responsible for the variations that Darwin observed.
Pre-Darwinian ConceptsPost-Darwinian Concepts Earth is relatively young age was measured in thousands of yearsEarth is relatively old age is now measured in billions of years Fixity of Species organisms do not change and the number of species has remained the same Organic Evolution organisms change and several new species can arise from a single ancestor A creator previously decided the structure and function of each type of organism Adaptation to environment explains structure and function of each type of organism Observation and experimentation are unnecessary to substantiate self-evident truth Observation and experimentation are used to substantiate theories of evolution.