Darwin’s Theory of Evolution

Chapter 15

Dr. Donna HowellBiology I

Blacksburg High School

Evolution• Well-

supported scientific theory

• Change over time

Charles Darwin• Scientist who,

in 1831, traveled on the HMS Beagle around the world to study nature.

• He made observations and collected evidence about how life changes over time.

Charles Darwin• He observed

that plants and animals all seemed well-suited to the environment they lived in

• He also noticed that certain species lived in some places but not in others.

Charles Darwin• He collected many preserved fossils ,

and wondered why some of these species had disappeared from the earth.

The Galapagos Islands• This was an area

in the Pacific that intrigued Darwin the most.

• He observed that the animals on the islands of the Galapagos differed in predictable ways.

The Ancient Changing Earth

• James Hutton and Charles Lyell propose that the Earth is shaped by geological forces that took place over millions of years

• Darwin wondered if the same could be true for life

Lamarck’s Hypothesis• Lamarck

hypothesized that through use or disuse of organs, living beings could add or lose traits in their lifetime.

Lamarck’s Hypothesis• An example of

this is the fiddler crab.

• He said that because the male crab uses its large claw a lot, it becomes larger

• This larger claw is passed on to offspring.

Population Growth• Thomas Malthus,

in 1798, said that if the human population continued to grow like it is, sooner or later there would be insufficient food and living space for everyone.

On The Origin of Species

• Darwin took all of these ideas, and came up with his own theory of evolution.

• In 1859, his book was published where he said a mechanism called natural selection was responsible for change.

Inherited Variation• Darwin learned

from animal and plant breeders that some of this change was due to inheritance – differences passed from parent to offspring.

Artificial Selection• When certain

plants and animals are deliberately bred to produce a superior organism, this is called artificial selection.

Natural Selection• Darwin realized

that artificial selection takes place in nature.

• There is a struggle for existence between organisms, and those that have better traits win.

Natural Selection• Darwin also said

that those organisms that were better suited to their environment survived to reproduce, passing their traits on.

• Survival of the fittest

Natural Selection• Darwin also said

that each living species has descended, with changes, from other species over time to best suit their habitat.

• Descent with modification.

Natural Selection• Darwin said that

if we trace the lineage of each animal back, we would find that all shared a common ancestor.

• Common descent.

Evidence of Evolution• There are multiple types of evidence for

evolution.• Fossil record, homologous body

structures, and embryology.

The Fossil Record• By comparing

fossils from different rock layers, scientists can document the fact that life on Earth has changed over time.

Homologous Body Structures

• Scientists have noted that although arms, wings, legs, and flippers are very different, they all are constructed from the same bones.

• Called homologous structures.

Embryology• The early stages of

animals with backbones are very similar.

• Same groups of embryonic cells develop in the same order and similar patterns to produce tissues and organs.

Summary• Individual

variations can be inherited.

• Only the fittest survive

• Natural selection causes species to change over time.

• Species today are descended with modification from ancestral species.