Chapter 15

Darwin’s Theory of Evolution

Charles Darwin Born February 12, 1809

– Died April 19, 1882 English Naturalist Sailed the world in 1831

on a 5 year voyage aboard the H.M.S. Beagle

Galapagos Islands!!!! Began the modern

perspective on the theory of evolution

Origin of Species (1859)

The Descent of Man (1871)

15-1 The Puzzle of Life’s Diversity

Charles Darwin collected over 3,000 different species of plants and animals

The species varied per island Insects, reptiles and birds were the most

influential to Darwin Many species showed evolutionary diversity

varying from fossil records Provided evidence which would forever

change Biology

“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"

Monkeys to Man?

The Descent of Man challenges the scientific community to believe man has evolved from a preexisting form, primates.

Like other species, man has evolved from primitive unicellular organisms through primates to what we now recognize as humans beings, Homo sapiens.

What does Darwin mean?

In the random shuffle of heredity, all organism’s of the same species are born slightly different.

This slight difference gives them the “edge” to survive

The cruelty of nature challenges species’ to struggle for survival

Nature selects the “better” organism to survive

Darwin’s theory of Natural Selection was born

15-2

Ideas That Shaped Darwin’s Thinking

Hutton and Lyell:

(1700’s) James Hutton & Charles Lyell first suggested the Earth was changing over time.

Recognized the Earth was millions of years old.

They believed the same “Earth changing processes” were always in effect.

1795 James Hutton published his theory of geological forces which changed Earth.

Proposed the Earth was more than a few thousand years old.

Charles Lyell published Principles of Geology. Theorized that processes occurring now have

shaped the Earth’s geological features over very long periods of time.

BOTH Hutton and Lyell influenced the way Darwin thought about the ever changing Earth.

Jean-Baptiste Lamarck

One of the first to recognize that living organisms changed over time.

1809, Lamarck published his theory on how organisms changed.

He proposed that by selective use or disuse of organs, organisms lost or gained certain traits during their lifetime. Over time, the changes led to a change in an entire species.

Proposed all organisms wanted their species to be perfect.

Was Lamarck correct?

He was incorrect in several ways. An organism’s behavior has no effect on its

inheritable characteristics. YOU have NO control over the traits you

inherit. Lamarck was one of the first to develop a

scientific theory of evolution.

Thomas Malthus

1798, an English economist named Thomas Malthus realized that people were being born faster than they were dying.

He realized that limiting factors were a major concern for population growths

He theorized that war, famine and disease limited the growth of the human population.

15-3

Darwin Presents His Case

Natural Variation and Artificial Selection

Darwin argued popular belief by stating that natural variation was found in all types of organisms

Natural variation is the differences found among individuals of the same species

For example, zebra stripes milk production in cows

Through artificial selection breeders can alter natural variation

With artificial selection, humans interfere with the natural process to select the “best.”

Humans select the naturally occurring variation

Natural Selection

Darwin believed in the process of natural selection results in changes of a species over time to better adapt to their environment.

He referred to this as the survival of the fittest, individuals more suited to their environment will survive and reproduce more successfully.

He believed fitness was a result of adaptations. Also believed that a species must overcome a

struggle for existence by obtaining food, living space, and other life necessities like shelter.

Ancestors?

Darwin proposed that all species had ancestors He referred to this as descent with modification Each species had descended with change over time Darwin theorized that if we looked back far enough,

we could find evidence of a common ancestor among all species.

Known as common descent In early stages, chickens, turtles and rats look similar

providing they shared a common ancestor These are known as homologous structures