Darwin’s Theory of Evolution

1. Darwin’s Theory of Evolution Chapter 15

2. Definitions to know: • Evolution: change over time • Theory: a well-supported, testable explanation of phenomena that have occurred in the natural world.

3. Voyage of the Beagle • Charles Darwin , born 1809 • Was a naturalist • 1831 sailed around the world in the HMS Beagle

4. During his travels, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time. • On Darwin’s journeys, he drew and sketched the world around him, and kept a journal of his observations. • He collected insects and other small organisms. • He collected fossils ( the preserved remains of ancient organisms). • He is most known for his study of the Galapagos Islands where he made note of the different varieties of finches, their characteristics, and their habitats. Play video

5. Ideas that shaped Darwin’s thinking • Fossil record • Hutton: geologic forces change the earth’s surface and it occurs over millions of years, therefore the earth is more than 1000 years old. • Lyell: geologic features are built up/torn down over long periods of time. • Lamarck: by selective use/disuse of organs, organisms acquire/lose certain traits during their lifetime, traits are passed to offspring, there fore change occurs in populations over time. • Malthus: if the human population continues to grow unchecked, sooner or later there would be insufficient living space and food for everyone. • Farmers: used artificial selection to capitalize on desired traits and incorporate them into the offspring of their breeding stock.

6. Evolution by Natural Selection • Darwin was convinced that a process like artificial selection was at work in nature. • He called it Natural Selection (survival of the fittest). • Fitness is the result of adaptation. • Adaptation: an inherited characteristic that increases an organism’s chance of survival. • Adaptations are the result of random mutations that contribute to the organisms fitness. • Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.

7. Descent with Modification • Darwin proposed that over long periods of time, natural selection produces organisms that have different structures, establish different niches, or occupy different habitats. • Each living species has descended, with changes, from other species over time. • It implies that the species are related and have common ancestors (living and extinct)- common descent.

8. Evidence of Evolution • The fossil record • Geographic distribution of living species: similar habitats = similar selection pressures = similar looking organisms. • Homologous body structures: structures that have different mature forms but develop from the same embryonic tissues.

9. Not all homologous structures are important. Vestigial Organs: organs that are no longer used by the body (ex: appendix, wisdom teeth). • Similarities in embryology:

10. Summary of Darwin’s Theory • Individuals differ and some of this variation is heritable. • Organisms produce more offspring than can survive , and many that do survive, do not reproduce. • Because more organisms are produced than can survive, they compete for limited resources. • Each organism has unique advantages and disadvantages in the struggle for existence. Individuals best suited for their environment survive and reproduce most successfully. Other individuals die or leave fewer offspring. The process of natural selection causes species to change over time. • Species that are alive today are descended with modification from ancestral species that survived in the past (common ancestors).