How old is Earth?
Earth is now believed to be over 4.5 billion years old. But during Darwin's time, most people believed that the Earth was only about 6,000 years old. If Darwin hadn't learned about the work of geologists that suggested that the earth was much older, he might have never have developed his theory of evolution.
When Darwin returned to England five years later, in 1836, at the end of his voyage, he did not rush to announce his discoveries. Unlike other naturalists before him, Darwin did not want to present any ideas unless he had strong evidence supporting them. Instead, once Darwin returned to England, he spent over twenty years examining specimens, talking with other scientists and collecting more information before he presented his theories.
Some of Darwin’s ideas conflicted with widely held beliefs, including those from religious leaders. At that time, many people believed that organisms never change and never go extinct, and that the world was only about 6,000 years old. These beliefs delayed Darwin in presenting his findings.
How did Darwin come up with his theories? Charles Darwin was influenced by the ideas of several people.
- Before the voyage of the Beagle , Jean-Baptiste Lamarck proposed the idea that species change over time. However, Darwin differed with Lamarck on several key points. Lamarck proposed that traits acquired during one’s lifetime could be passed to the next generation. Darwin did not agree with this.
- The findings of Charles Lyell , a well-known geologist, also influenced Darwin. Lyell's writings taught Darwin about geology, paleontology, and the changing Earth. Lyell's findings suggested the Earth must be much older than 6,000 years.
- After the Voyage of the Beagle , another naturalist, Alfred Wallace ( Figure below ), developed a similar theory of evolution by natural selection. Wallace toured South America and made similar observations to Darwin's. Darwin and Wallace presented their theories and evidence in public together. Due to the large number of observations and conclusions he made, Darwin is mostly credited and associated with this theory.
Alfred Wallace developed a similar theory of evolution by natural selection.
- Lamarck (Jean Baptiste Lamarck) : French naturalist; one of the first scientists to propose that species change over time.
- Lyell (Charles Lyell): English geologist; he claimed that Earth must be much older than most people in the 1800s believed.
- Wallace (Alfred Russel Wallace): English naturalist; he developed a theory of evolution similar to Darwin's.
- Darwin’s ideas conflicted with widely held beliefs, such as the idea that organisms never change and that the world was only about 6,000 years old.
- Darwin was influenced by other scientists, including Lamarck, Lyell, and Wallace.
Use the resource below to answer the questions that follow.
- An Introduction to Uniformitarianism at http://www.youtube.com/watch?v=H9iuiBPc0tE (3:04)
- Who first proposed that the Earth was far older than people thought?
- What book by Charles Lyell did Darwin bring on his voyage? Why was this book significant?
- What does "the present is the key to the past" mean in regard to geology? Do you think this phrase could apply to biology as well? Explain your reasoning, and be as specific as you can.
- What is the "Principle of Geological Actualism"? How does it differ from Uniformitarianism?
- Nova: Great Minds Think Alike at http://www.pbs.org/wgbh/nova/evolution/great-minds-think-alike.html .
- Where did Wallace travel? How did he pay for his trips?
- What happened to the collections Wallace sent to England from South America?
- How does the scope and geography of the Malay Archipelago compare to the Galapagos Islands?
- What did Wallace make special note of in his collections that Darwin failed to do? How was this key to the development of his theory?
- What is the Wallace Line?
- Compare and contrast Darwin's and Lamarck's views of evolution.
- Why did Darwin hesitate to publish his theory?