The Evolution of The Evolution of Evolutionary Evolutionary

TheoryTheory

Theory vs FactTheory vs Fact

Scientific Theory: Scientific Theory: “A well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment.“

Theory vs FactTheory vs Fact

Scientific Fact: Scientific Fact: Scientists most often use the word "fact" to describe an observation. But scientists can also use fact to mean something that has been tested or observed so many times that there is no longer a compelling reason to keep testing or looking for examples. 

Theory? Fact? Both?Theory? Fact? Both? "Darwin continually emphasized the difference

between his two great and separate accomplishments: establishing the fact of evolution, and proposing a theory—natural selection—to explain the mechanism of evolution.“

Scientists continue to argue about particular explanations or mechanisms at work in specific instances of evolution, but the fact that evolution has occurred and is still occurring is undisputed.

James Hutton (1726-1797) and James Hutton (1726-1797) and Charles Lyell (1797-1875)Charles Lyell (1797-1875)

Studied the forces of wind, water, Studied the forces of wind, water, earthquakes and volcanoes. earthquakes and volcanoes.

They concluded the earth is very old and They concluded the earth is very old and has changed slowly over time due to has changed slowly over time due to natural processesnatural processes

Erasmus Darwin(1731-1802)Erasmus Darwin(1731-1802)

Suggested that competition between Suggested that competition between individuals could lead to changes in individuals could lead to changes in species.species.

He was also Charles Darwin’s He was also Charles Darwin’s grandfather.grandfather.

Jean Baptiste Lamarck Jean Baptiste Lamarck (1744-1829)(1744-1829)

The first scientist to propose a system of The first scientist to propose a system of evolution.evolution.

Noticed that fossils became more Noticed that fossils became more complex in earlier rock strata, therefore a complex in earlier rock strata, therefore a drive towards complexity.drive towards complexity.

Each species came from less complex Each species came from less complex onesones

Lamarck (continued)Lamarck (continued)

Believed that evolution is based on Believed that evolution is based on 2 principles:2 principles:

1.1. Law of use and disuseLaw of use and disuseThe more an animal uses a The more an animal uses a certain part of the body, the certain part of the body, the stronger and better developed it stronger and better developed it becomesbecomes

2.2. Inheritance of acquired Inheritance of acquired characteristics characteristics Characteristics Characteristics an organism developed through an organism developed through use and disuse could be passed use and disuse could be passed on to its offspringon to its offspring

Thomas Malthus (1766-Thomas Malthus (1766-1834)1834)

Observed that human Observed that human populations cannot keep populations cannot keep growing indefinitely.growing indefinitely.

If the birth rate continued If the birth rate continued to exceed the death rate, to exceed the death rate, eventually humans eventually humans would run out of space would run out of space and food.and food.

Famine, disease and Famine, disease and war prevented endless war prevented endless population growth.population growth.

Charles Darwin Charles Darwin (1809-1882)(1809-1882)

Formulated a theory of evolution by Formulated a theory of evolution by natural selection based on observations made natural selection based on observations made during his voyage on the Beagle, and of selective during his voyage on the Beagle, and of selective breeding of farm animals, plants and pets.breeding of farm animals, plants and pets.

He drafted manuscripts outlining his theory in the He drafted manuscripts outlining his theory in the 1840s but hesitated to release them to the 1840s but hesitated to release them to the public.public.

His most famous work His most famous work On the Origin of Species On the Origin of Species by Means of Natural Selection by Means of Natural Selection was published in was published in 1859.1859.

Darwin’s Theory:Darwin’s Theory:

Overproduction: more offspring are produced Overproduction: more offspring are produced by an organism than can possibly survive.by an organism than can possibly survive.

Competition: high birth rates cause a shortage Competition: high birth rates cause a shortage of life’s necessities leading to competition of life’s necessities leading to competition between organisms.between organisms.

Variation: each individual differs from all other Variation: each individual differs from all other members of its species; some differ more than members of its species; some differ more than others.others.

Darwin’s Theory (continued)Darwin’s Theory (continued)

Adaptation: allows organisms to become Adaptation: allows organisms to become better suited to their environment.better suited to their environment.

Natural Selection: the most fit (best Natural Selection: the most fit (best adapted) organisms survive and adapted) organisms survive and reproduce.reproduce.

Speciation: formation of new species Speciation: formation of new species from ancestral species by means of from ancestral species by means of natural selection.natural selection.

Alfred Russell Wallace Alfred Russell Wallace (1823-1913)(1823-1913)

Proposed a theory of evolution Proposed a theory of evolution by natural selection similar to that by natural selection similar to that of Darwin.of Darwin.

He wrote a paper and sent it to Darwin to He wrote a paper and sent it to Darwin to review. This paper spurred Darwin on to finally review. This paper spurred Darwin on to finally agree to the release of his theory.agree to the release of his theory.

In 1858, Charles Lyell presented Darwin’s In 1858, Charles Lyell presented Darwin’s 1844 essay and Wallace’s paper to the public.1844 essay and Wallace’s paper to the public.

Darwin SONG!Darwin SONG!

http://www.youtube.com/watch?v=Pt2gHpqfZNA