Chapter 32 Theories of Evolution

Introduction• Biologists have classified more than 1.5 million

species of organisms for far.• Many scientists estimate that there may be 10

million species of organisms living on earth.***Review Classification• What does a Scientific name consist of?

1. Kingdom order2. Class species3. Phylum Genus4. Genus species

Classification Review

• What is the correct way of writing the scientific name for a Lion?

1.panthera leo

2.Panthera leo

3.Panthera leo

4.panthera Leo

Introduction cont.• As we know there are differences between

organisms of different species.• In addition, there are also differences among

organisms of the same species (variations).

Why are there so many variations among organisms?

• Evolution is responsible for this great diversity!• Evolution: the process by which organisms

change over time.

Evolution• Until the 19th century, most scientists believed that organisms existed as they had first appeared on earth.

• However, by the 1800’s geologists were finding and studying many fossils.

• What do you think these fossils showed?

• Scientists began wondering how and why living things may have changed?

Evolution cont.During this time 2 biologists proposed a theory on evolution:

Lamarck's Theory• Proposed his theories in 1809• 1st hypothesis:–Organisms develop traits, or characteristics by

the use or disuse of body parts.• Ex: If the body part is used, it becomes

larger and stronger. If the body part is not used, it becomes smaller and weaker.

Lamarck's Theory cont.

• 2nd hypothesis:–Acquired characteristics, or the traits that

organisms develop during their lifetimes, are passed from parents to their offspring• Ex: Giraffe

• He didn’t have any observations or evidence to support his theory.

• Therefore most scientists did not support his theory.

Lamarck's Theory cont.

Investigations of Charles Darwin• British Naturalist born in 1809.• At the age of 22 Darwin voyaged on the HMS

Beagle.• HMS Beagle went on a mapping and collecting

expedition to South America and the South Pacific.

What did Darwin observe during his 5 year voyage?

• How earthquakes and other geological processes change the land.

• He observed thousands of species of plants and animals

• Collected fossils• Notes on all his observations

Darwin’s Finches

Darwin’s Theory of Evolution• 20 years after his voyage, he published a book

called On the Origin of Species by Means of Natural Selection.

• What are Darwin’s main ideas about evolution?1.Overproduction2.Competition3.Variations4.Survival of the Fit

Darwin’s Theory of Evolution cont.1. Overproduction: Each species produces many

more organisms than can survive and reproduce.

• Ex: Crabs, codfish, salmon, sea turtles

Darwin’s Theory of Evolution cont.

2. Competition: due to overproduction of offspring, organisms must compete for limited resources (food, water, & a place to live)

Darwin’s Theory of Evolution cont.3. Variation: differences among traits, occur

among members of the same species.

Darwin’s Theory of Evolution cont.

4. Survival of the Fit: Organisms with traits that make them well adapted to their environment have a better chance to surviving and reproducing (natural selection).

Darwin’s Theory of Evolution cont.

• Organisms that survive and reproduce pass on their traits to their offspring.

• As the process of natural selection continues through many generations, species change and become better adapted to their environment.

• As a result, evolution occurs by natural selection.