The Evolution of EvolutionHistoric Ideas about Organism Change

Aristotle(384 - 322 B.C.)

● “Ladder of life”● Nature is ordered from

lower to higher● No vacant rungs● No movement up or

down the ladder● Included living and

non-living things

Jean-Baptiste Lamarck (1744-1829)

● First scientist to propose a mechanism for how organisms change (1809)

● His idea: “Inheritance of Acquired Traits”● Greater use of a body part

would change it, and the change would pass on to the organism’s offspring.

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.

Lamarck’s Assumptions

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.

Lamarck’s Assumptions

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

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

Charles Darwin(1809-1882)

● English naturalist● Traveled around the world on the Beagle (1831); famously stopped in the Galapagos Islands

● Observed many species and fossils

● Particularly studied finches, tortoises, blue-footed boobies

The Galapagos Islands (Ecuador)

“Darwin’s finches”● Darwin noticed that

finches were different on each Galapagos Island.

● He concluded that the different finches had descended from a common ancestor and had changed to be able to do and eat different things.

Darwin’s “Descent with Modification”After his studies, Darwin came up with 4 main ideas…

1. Individuals differ, and some of this variation can be inherited.

2. Organisms produce more offspring than can survive; thus they have to compete for resources, and only the most fit will survive and reproduce.

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

4. Species alive today are descended with modification (change) from their ancestors.

“Descent with modification” means…

…change in organisms over time (many generations)

“Natural Selection” means…

… “pressure” the environment puts on the specific traits that affects their ability to survive

Hey! I thought this unit was about evolution??

“Evolution” means…

… change over time

Therefore we now call Darwin’s idea “biological evolution.”

“Descent with modification” definitions

Lamarck’s explanation for the giraffe’s long neck:

Darwin’s explanation for the giraffe’s long neck:

Darwin was influenced by the work of others… Thomas Malthus – Populations James Hutton and Charles Lyell – Geological

Record Farmers – Breeding

Thomas Malthus(1766-1834) British clergyman and scholar

His prediction: the human population

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

The only checks on the human population would be war, famine, and disease.

Influence of Malthus on Darwin

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?

James Hutton and Charles LyellBritish Geologists

Hutton is considered the “father of modern geology”

Based on layers found in rock structures, Lyell proposed that Earth is millions of years old

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

Grand Canyon, Arizona

Influence of Geology on Darwin

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

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

Farmers

Farmers recognize that within a population, there is natural variation.

Farmers improve their plants and animals through selective breeding.

Influence of Farmers on Darwin

Farmers bred the plants or animals with the most desired traits.

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