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Evolution: History and Theory

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What is Evolution?: Fact vs. Theory Evolution is the change in

the genetic make up of populations over time.

All living things change. Evolution is a fact. Populations evolve, not

individuals.

The mechanism for evolution (how it happens) is a theory. The theory of natural selection is a well supported, testable explanation of how evolution occurs.

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Jean-Baptiste Lamarck (1744-1829) First scientist to propose a

mechanism for how organisms change (1809)

Theory of Acquired Traits Through time, a generation

would use an organ more than previously, and would pass those traits on to their offspring.

Lamarck did not know about the inheritance of traits through the passing of genes.

ACQUIRED traits can NOT be inherited.

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Lamarck’s Assumptions

1. Organisms have a desire to change. They have an inborn urge to better themselves for their environment.

Ex: Birds tried to fly and eventually grew wings because of their efforts.

2. Organisms can change shape by using or not using their bodies.

Ex: The wings of a bird that does not fly would get smaller from generation to generation and the wings would eventually disappear.

3. Organisms can pass on acquired traits to their offspring.

Ex: If an animal developed muscles from running during its lifetime, it could pass those muscles on to its offspring.

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Who was Charles Darwin? (1809- 1882) English naturalist Traveled around the world on the

Beagle (1831)—Famous in the Galapagos Islands

Observed many species and fossils

Devised his theory of evolution.

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Thomas Malthus Essay on the Principle of

Population (1798) He predicts that the human

population will grow faster than the space and food supplies needed to sustain it.

Stated that the only checks on the human population were war, famine, and disease.

Influence of Malthus

Malthus’ theory of population growth was observed by Darwin in other animal populations as well.

In nature, Darwin saw many organisms that produced many offspring. Most died.

Darwin wondered, what determines which individuals survive and reproduce?

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James Hutton and Charles Lyell Hutton is the father of

modern geology Based on layers found in

rock structures, he proposed the Earth was millions of years old (1785)

Lyell proposed that geological features could be built up or torn down over long periods of time (1833)

Influence of Lyell

After reading Lyell’s book, Darwin was convinced that the Earth was old.

Darwin reasoned that if geological phenomena could change the earth, then life on Earth could change as well.

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Influence of Farmers

Within a population, there are natural variations.

Farmers improved their plants and animals through selective breeding.

Farmers bred the plants or animals with most desired traits.

This process of humans allowing only the best organisms to reproduce is called artificial selection.

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“Survival of the Fittest” Fitness is the ability of an

organism to survive and reproduce in its environment.

Ex: An animal that can easily avoid predators and mates regularly has higher fitness than an individual that does not mate.

Individuals in nature with characteristics best suited to their environment survive the struggle for existence.

This principle is called survival of the fittest.

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Natural Selection

The process by which nature allows only the organisms best suited to their environment to reproduce is called natural selection.

I have called this principle, by whicheach slight variation, if useful, is preserved,

by the term Natural Selection.    —Charles Darwin from "The Origin of Species"

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Peppered MothThere are two variations in

color of peppered moths, light and dark.

Prior to the industrial revolution, tree trunks were light colored.

Predators were more likely to pick the dark moths. As a result, the moth population was primarily light.

After the industrial revolution, trees were covered in soot making them dark.

Now, predators were more likely to pick the light moths. As a result, the population shifted from being primarily light to primarily dark.

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Darwin’s Theory – A Summary

Individual organisms differ, and some of this variation is heritable.

Organisms produce more offspring than can survive. Thus, organisms have to compete for resources. Only the most fit organisms survive and reproduce.

The most fit organisms pass on their heritable traits to their offspring.

Species alive today are descended with modification (change) from ancestral species.

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What is a Niche? How does a niche affect fitness?

A niche is the full range of physical and biological conditions in which an organism lives

and also

the way in which the organism uses those conditions.

An organism’s fitness is higher within its niche than outside of its niche.

Ex: A penguin’s fitness is higher in Antarctica than in Elizabethtown.

Why?

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Different Niches for Different Beaks

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Adaptive Radiation

Adaptive radiation is the process by which a single species evolves into several different forms that live in different ways.

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ADAPTIVE RADIATION –An example of divergent evolution

http://evolution.berkeley.edu/evolibrary/home.php

http://www.vanderbilt.edu/AnS/english/Clayton/Galapago_finches.gif