Historical Background to the Theory of Evolution

Evolution= A change over time in the genetic composition of a population.

Aristotle n all living forms could be arranged on a scale of increasing complexity “scala naturae” (scale of nature) n no vacancies and no mobility in this ladder of life n species are fixed, permanent, and do not evolve (Stability of Species)

Carolus Linnaeus : Swedish physician and botanist: father of taxonomy He believed that species were permanent creations, “God creates, Linnaeus arranges” Ironic because Darwin uses this taxonomy system as a focal point for evolution

Georges Cuvier ( ): Founder of Paleontology (the study of fossils) Opposed evolution Thought that boundaries between fossil layers corresponded to catastrophic events such as Noah’s flood or droughts Developed the theory of catastrophism

James Hutton:( ) Scottish Geologist In 1795 suggested Gradualism, profound change is the cumulative product of slow but continuous processes He looked a present day processes like erosion by water. Believed these processes operating over millions of years could have created the geologic features we see today. Therefore the Earth was very old

Charles Lyell ( ): Uniformitarianism Embellished Hutton’s gradualism, geological processes are so uniform that their rates and effects must balance out through time Suggested the Earth was hundreds of millions of years old. Darwin took only three books with him on the Beagle. One was Lyell’s book Principles of Geology

Jean Baptiste Lamarck ( ) published a theory of evolution in 1809 (year Charles Darwin was born) Believed that evolution responded to organisms “felt needs” use and disuse: examples: biceps of blacksmith, giraffes neck - inheritance of acquired characteristics: modifications acquired during a lifetime can be passed on to offspring no evidence for this Ex mice tails

Thomas Malthus n believed that human suffering was a consequence of overpopulation. n -If resources were scarce, some organisms will not survive.

DARWIN n Darwin used 2 ideas from Hutton and Lyell: n If geological changes results from slow continuous changes then earth must be older than 6000 years (natural theologian calculation) n Very slow and subtle processes persisting over a great length of time can cause substantial change

In 1831 he left on a 5 year voyage on board the Beagle to survey the coast of South America. He stopped off in the Galapagos Islands where the diversity of tortoises and birds amazed him In 1836 he returned to England In 1859 published On the Origin of Species What ideas influenced Darwin?

Darwin’s Finches

Darwin saw variation within species on the different Islands. But didn’t fully understand what he saw till he returned to England

From Geologists Hutton and Lyell he knew the Earth was old. The Economist Malthus explained population growth to Darwin Populations breed rapidly But populations don’t grow unchecked Most organisms in a population die without breeding From his observations he could see variation within species. We can summarize Darwin’s theory of Natural Selection in the following way….

Darwin’s Theory of Natural Selection 1.Organisms reproduce like organisms (themselves) 2.In most species only a small percentage will actually survive to reproduce 3.There are variations in individuals in a given population & these traits can be passed on. (caused by mutations)

4.Whether an individual will survive to breed depends upon the interaction between these variations & the environment. Some variations will be favorable. These variations will become more common from one generation to the next. The process is called Natural selection Variations that are favorable will help you What makes a successful variation? One that makes it more likely for you to: Get food Not get eaten Have children Thermal conservation 5. Given time, natural selection will produce different groups of organisms (speciation)

3 MAJOR FACTORS INFLUENCING DARWIN The age of the earth (Lyell) Population controls (Malthus) Breeding programs-aka Artificial Selection (Farmers)

NATURAL SELECTION The process in nature where the most fit organisms produce more offspring

Natural Selection: If variation of a trait within a population has a genetic basis, and some variants have greater survival and reproduction, then, over time, the favored trait will predominate in the population.

Requirements:  More individuals are born each generation than can survive: the "Struggle for Existence"  Variation in a trait within a population. (Giraffe's necks)

 Giraffes with longer necks get better food, have more babies (greater fitness)  Longer necks give birth to longer necks (trait is passed on in genes)

Results: Over time, average neck length increases

Under other conditions, over longer periods of time, new species form (e.g. the Okapi)