15.2 – Ideas That Shaped Darwin’s Thinking

Interest Grabber My, How You’ve Changed! Section 15-2 My, How You’ve Changed! Prior to the 1800s, life scientists knew that living things changed over generations. They just didn’t know how these changes were brought about. 1. Divide a sheet of paper into two columns and title the first one Inherited Characteristics. Title the second column Acquired Characteristics. In the first column, list the characteristics that you believe you have always had. For example, you may have brown eyes or curly hair. 2. In the second column, list your acquired characteristics. For example, you may have learned how to play a musical instrument. 3. Which of the items in your lists do you think you might pass on to your children? Explain your answer.

Darwin’s Ideas Darwin greatly changed the thinking of many scientists, but also many did not believe him Most Europeans at the time believed Earth was only created a few thousands of years before present time They believed everything was created the way it was and never changed By the time Darwin set sail there was a rich fossil record challenging this idea

Lamarck’s Theory of Evolution One of first scientists to recognize things have changed over time He also recognized organisms were adapted to their environment He proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime And then be inherited

Lamarck’s Examples

Lamarck’s Theory of Evolution Section 15-2 Fiddler Crab example 2. Use and disuse Waving to attract mates Tendency towards perfection Changing to live more successfully 3. Inheritance of acquired characteristics

Objective: Summarize Lamarck’s theory of evolution through inheritance of acquired characteristics Jean Baptiste Lamarck (1744-1829) Assumed that body parts used more frequently become stronger and more developed Assumed acquired characteristics were inheritable Predictions based on a hypothesis can be stated in an if . . . then format If dog ears cropped, then offspring will be cropped. Not supported If parents weight lift, then children will have well-developed muscles.

Lamarck’s Theory His theory is incorrect in several ways He didn’t know how traits are inherited He did not know that an organism’s behavior has no effect on its inheritable characteristics He was one of the first to develop the Theory of Evolution and realize animals adapt to their environment

Population Growth In 1798, Thomas Malthus saw babies were being born faster then people were dying He reasoned if that continues to happen the time might come when there is insufficient land and food on Earth to support the population size Does this apply to all living organisms? Darwin realized this reasoning applied even more strongly to plants and animals than it did to humans. Humans produce far fewer offspring The overwhelming majority of a species’ offspring die