Lesson Summary

In this lesson you explored the following essential questions:

• How do theories explaining evolutionary change compare?
• What theories attempt to explain the pace of evolutionary change?

In this lesson, you examined theories that led Charles Darwin and Jean-Baptiste Lamarck to create their own theories about evolution. Both scientists believed that organisms with beneficial adaptations to the environment would survive.

The difference between the theories is how these organisms obtained their adaptations. Lamarck believed organisms could acquire their adaptations during their lifetimes, whereas Darwin thought that organisms were born with traits, which were then selected by nature. Over time, Darwin proposed that these beneficial traits would build up in a population, causing the population to change or evolve.

In Lamarck's view, evolution occurs within a single generation or within a few generations. Darwin's view suggests that evolution occurs over many generations and a long period of time. Many modern scientists accept Darwin's theory of evolution by natural selection to be true. However, there is a debate about the pace of evolution. Does evolution happen gradually or in punctuated bursts of divergence?

As you learn more about evolution, you will find that it is still an evolving topic in science. The discovery of new species and the risk of extinction of others make the study of speciation and evolution relevant today.  In Lesson 3 you will look at the evidence scientists use to prove evolution has occurred and the evidence they use to study evolutionary relationships.

 Lesson Glossary

hypothesis: a statement that provides one possible answer to a question or one possible explanation for an observation

theory: a well-supported, widely accepted explanation for the events in the natural world

law: a statement that describes a natural phenomena 

inheritance of acquired characteristics: the theory that characteristics acquired during an organism's lifetime could be passed to its offspring

fossils: the remains of past life found in sedimentary rock

paleontology: the study of ancient life through the examination of fossils

gradualism: gradual change occurs in a steady, linear way over time

punctuated equilibrium: evolutionary history is said to consist of long periods of equilibrium, interrupted by periods of speciation

 Assessments

Complete Unit B: Section 3 Assignment now.