1. Ideas That Shaped Darwin’s Thinking Ch 15-2

2. Darwin’s voyage came during one of the most exciting periods in the history of Western science. If he’d lived in an earlier time, Darwin might have done nothing more than think about the questions raised during his travels… but in Darwin’s day, great thinkers were beginning to challenge the established and traditional views about the natural world. Darwin was powerfully influenced by the work of these scientists, especially those studying the history of the Earth. In turn, his work greatly changed the thinking of many scientists and non-scientists alike.

3. Some people, however, found Darwin’s ideas too shocking to accept. To understand how radical Darwin’s thoughts appeared, you must understand a few things about the world in which he lived. Most European people believed that Earth and all its life forms had been created by God only a few thousand years ago. Since that creation, they concluded, neither the planet nor its life forms had changed. Rocks and major geological features were thought to result from sudden catastrophic events that humans rarely, if ever, witnessed.

4. By the time Darwin set sail, numerous new discoveries had resulted in a rich fossil record that was challenging the traditional view of life. Some scientists were adjusting their beliefs to include not one, but several periods of creation. Each of these periods, they reasoned, was preceded by a catastrophic event that killed off many forms of life. Darwin began to realize that what he had observed did not fit neatly into this view of unchanging life. Slowly, and after studying many scientific theories of the time, Darwin began to change his thinking dramatically.

5. James Hutton’s Ancient, Changing Earth During the 18th and 19th centuries, scientists examined Earth in great detail and gathered information suggesting that it was very old and had changed slowly over time. In 1795, geologist James Hutton, published a detailed hypothesis about the geological forces that have shaped earth. Hutton proposed that layers of rock form very slowly. He added that some rocks are moved up by forces beneath Earth’s surface, others are buried, and still others are pushed up from the seafloor to form mountain ranges. All these rocks, mountains, and valleys are then shaped by a variety of natural forces, including rain, wind, heat, and cold temperatures. Most of these geological processes take millions of years to occur, therefore, Hutton proposed that Earth had to be much older than just a few thousand years as believed.

6. Charles Lyell stressed that scientists must explain past events in terms of processes that they can actually observe, since processes that shaped the Earth millions of years earlier continue in the present. Just before setting sail on the Beagle, Darwin was given a copy of Lyell’s Principles of Geology. Lyell’s work explained how geological features could be built up or torn down over long periods of time. This understanding helped Darwin appreciate the significance of the geological phenomena he witnessed -- including a volcanic eruption and an earthquake. His understanding of Lyell’s geological teachings influenced Darwin in two important ways: 1. First, Darwin asked: If the Earth can change over time, can organisms change as well? 2. Second, he realized that it would have taken many, many years for life to change in the way he was suggesting… this would be possible only if the Earth were extremely old.

7. Hutton and Lyell used geological features such as these huge sandstone rocks as evidence to show that Earth was many millions of years old rather than just a few thousand.

8. Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed onto their offspring. Over time, this process could lead to change in a species. Jean-Baptiste Lamarck, a French naturalist, was one of the first scientists to propose that living things have changed over time and that all living species were descended from other species. He also realized that organisms were somehow adapted to their environments. He published his hypothesis in 1809, the year Darwin was born. Unfortunately, his hypothesis was incorrect in many ways, but he was one of the first to develop a scientific theory of evolution and also to realize that organisms are adapted to their environments, paving the way for the work of later biologists.

9. Lamarck’s Evolution Hypotheses 1. Organisms are naturally inclined towards complexity and perfection, so if you want to fly… keep flapping your arms and eventually you’ll be able to! NOPE! 2. Selective use or disuse of an organ leads to a change in that organ that can be passed onto offspring, if you want to lose your wings, just stop flying and they’ll go away! NOPE! 3. Acquired characteristics can be inherited, so if you go to the gym and work on that six-pack… your children will have six-pack abs, too! NOPE!

10. Thomas Malthus, Population Growth, and Darwin Another important influence on Darwin came from a book published in 1798 by the English economist Thomas Malthus. Malthus noted that babies were being born faster than people were dying and reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone. Malthus observed that the only forces working against human population growth were war, famine, and disease. Darwin realized that Malthus’s reasoning applied even more strongly to plants and animals than it did to humans. Why? Because humans reproduce at a much slower rate than most other species do. In one summer, a single tree can produce thousands of seeds while one oyster can produce millions of eggs. If all those offspring survived, the world would be overrun in just a few generations! This does not happen because the overwhelming majority of a species’ offspring die. Further, only a few of those offspring that survive actually succeed in reproducing. What causes the death of so many individuals? What factor(s) determine which ones survive and reproduce and which do not? The answers to these questions became central to Darwin’s explanation of evolutionary change.

11. Origins of Evolutionary Thought: A Summary 1785, James Hutton proposes that Earth is shaped by geological forces that took place over extremely long periods of time. He estimates Earth to be millions (not thousands) of years old. 1798, Thomas Malthus predicts, in his Essay on the Principle of Population, that the human population will grow faster than the space and food supplies needed to sustain it. 1809, Jean-Baptiste Lamarck publishes his hypotheses of the inheritance of acquired traits. The ideas are flawed, but he is one of the first to propose a mechanism explaining how organisms change over time. 1831, Charles Darwin sets sail on the H.M.S. Beagle, a voyage that will provide him with vast amounts of evidence leading to his theory of evolution. 1833, Charles Lyell publishes his second and final volume of Principles of Geology, explaining that processes occurring now have shaped Earth’s geological features over long periods of time. 1858, Alfred Wallace writes to Darwin, speculating on evolution by natural selection, basd on his studies of the distribution of plants and animals. 1859, Charles Darwin publishes On the Origin of Species The groundwork for the modern theory of evolution was laid during the 1700s and 1800s. Charles Darwin developed the central idea of evolution by natural selection, but others before and during his time also built essential parts of the theory.

12. Find the Google Doc you created at the end of section 15-1 1. Create a new heading and label it, “ 15-2: Ideas That Shaped Darwin’s Thinking” 2. Answer the 5 Section Assessment questions found on p. 377 of your text. You must type the questions and the answers