Ch 15 “Darwin’s Theory of Evolution”

• Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms

• The theory can explain Earth’s biodiversity

• A scientific theory is an explanation of natural events that is supported by evidence

Charles Darwin• In the 1830s, Charles Darwin

sailed around the world• He made many observations

and collected evidence• He noticed that many plants

and animals were very well suited to their environment

• He collected fossils, some of which were unlike any creatures he had ever seen

• He wondered why the species in the fossils had disappeared

Darwin’s Observations on the Galapagos Islands

• The Galapagos Islands are near each other but have different climates

• Darwin noted that the characteristics of many animals and plants varied noticeably among the different islands

• He wondered whether animals on different islands had once belonged to the same species

Ideas That Shaped Darwin’s Thinking

• In Darwin’s day, most Europeans thought that the Earth and all of its life forms had existed for only a few thousand years

• They also thought that species did not change

• Some scientists of Darwin’s time began challenging these ideas and helped to develop Darwin’s Theory of Evolution

Contributing Scientists to Darwin’s Theory of Evolution

• Hutton and Lyell helped scientists recognize that Earth is many millions of years old, and that it had changed over time

• These ideas helped Darwin realize that life might change as well.

• Knowing that Earth was very old convinced Darwin that there had been enough time for life to evolve.

• Jean-Baptiste Lamarck was one of the first scientists to see that evolution occurred.

• He also recognized that organisms adapt to their environments

• He proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetimes.

• These traits, could then be passed on to their offspring which, over time, led to a change in the species

• Scientists now know that was incorrect, but his general ideas about adaptation was correct and influenced Darwin.

• Economist Thomas Malthus thought that if the human population kept growing, sooner or later there would be insufficient living space and food for everyone

Darwin’s On the Origin of Species• In his book, he supplied

evidence that evolution has occurred and explained how evolution occurs

• His theory is based on artificial selection where nature provides the variation, and humans select those variations they found useful

• He thought that a similar process occurs in nature and called it natural selection

Natural Selection• Individuals differ, and some of

the differences can be passed on to their offspring

• Individuals best suited to their environment survive and reproduce most successfully (survival of the fittest)

• Fitness results from adaptations that are inherited and increase an organism’s chance of survival

• Only the fittest organisms pass on their traits which leads to a change in species over time

The tortoises eat plants. On one island, plants growvery close to the ground. Which island is this most likely to be? Why?Which island most likely has sparse vegetation that is hard to reach?

Struggle for Existence

• There is competition for limited resources, or a struggle for existence

Evidence for EvolutionReasons for an incomplete fossil record:• Many species have lived in

environments where fossils do not form.

• Their bodies are eaten and/or scattered by scavengers.

• It is difficult to form a fossil from a soft bodied animal as opposed to a hard bodied animal.

Evidence for Evolution

• Homologous structures of living organisms.

• Similarities in bone structures suggest that vertebrates share a common ancestor

Evidence for Evolution

• Similarities in early development.

• Scientific advances have upheld most of Darwin’s hypotheses

• However, evolutionary theory continues to change as new data are gathered & new ways of thinking arise