1. 15-3 Darwin Presents His Case

2. Darwin’s Return Upon Darwin’s return to England in 1836, he began to take a close look at the specimens he brought back with him It was at this time he noted that the the species on the Galapagos were like none other elsewhere

3. Darwin did not publish his findings right away. This was due mainly because the ideas he presented radically changed current scientific thought His work was not published until 1859

4. Origin of Species In his work, “Origin of Species”, Darwin proposed a mechanism for evolution that he called natural selection He then presented evidence that suggests that the process of evolution has been taking place for millions of years

5. Natural Variation and Artificial Selection Darwin began his explanation by disregarding the idea that a species is perfect and unchanging. He argued that natural variation, the differences among individuals of a species, was found in all organisms

6. Darwin stated that this variation can be seen in all forms of life. He also stated that variation can be inherited During Darwin’s time, it was revolutionary to suggest that variation was a major feature of life.

7. Darwin also noted how human beings already note that variation exists and how we use it to our advantage He did this by looking at English farmers Farmers select only the fastest horses, fattest hogs, and high milk producing cows

8. This idea of selectively breeding an animal or crop based on their variation to improve the outcome Darwin termed, artificial selection In artificial selection, nature provides the variation and humans select those variations that they find useful

9. Evolution by Natural Selection Darwin was convinced that a process similar to artificial selection occurs in nature. In order to explain this he went back to Malthus’ observations on population growth

10. This lead Darwin to realize that high birth rates and a shortage of life’s basic needs would eventually force organisms into a competition for resources He called this the struggle for existence

11. Survival of the Fittest A key factor in the struggle for existence is how well suited an organism is to its environment This ability of an individual to survive and reproduce in its environment Darwin called fitness

12. Darwin also proposed that fitness is a direct result of adaptations Adaptations are any inherited characteristic that increases an organisms chance of survival What are some examples of adaptations?

13. This concept of fitness was central to the process of evolution by natural selection, which is the key idea behind Darwin’s work This means that organisms with the best adaptations, will have the highest level of fitness, and therefore survive more

14. Because of its similarity to artificial selection, Darwin referred to survival of the fittest as a type of natural selection The key difference being that with natural selection, the environment forces the selection of traits not humans

15. Descent with Modification Along with survival of the fittest darwin also proposed the idea of descent with modification. Darwin proposed that over long periods, natural selection produces organisms that have different structures and occupy different places.

16. The idea that organisms descend with modification also introduces another of Darwin’s theories The idea is that all organisms must be related to one another in some way, shape, or form This is the idea of common descent

17. Evidence of Evolution With his unified and dynamic theory of life, Darwin was finally able to explain his observations during his voyage aboard the Beagle He presented these observations as evidence for the theory of evolution

18. Darwin argued that living things have been evolving on Earth for millions of years Evidence for this process could be found in the fossil record, the geographical distribution of living species, homologous structures, and similarities in development

19. The fossil Record By the time that Darwin published his book, fossils were known to be evidence of once living organisms Darwin was the first to combine the idea that these organisms were developing over a period of time and used rock layers to help support his theory

20. Geographic Distribution of living species Because Darwin suggested that environments gave rise to different adaptations he needed to explain this with evidence He noted his observations on the Galapagos where he saw organisms with different features being found in different places

21. Homologous Body Structures Darwin studied living species as well to help support his theory By doing so, he noted that living organisms that had backbones all had similar structures that made up their limbs

22. These structures are similar in the embryonic form yet different in the adult form Darwin stated that this is because they develop from the same time of embryonic cells This is what Darwin calls homologous body structures

23. Darwin also noted that not all homologous structures served important functions These structures that are homologous but have no purpose anymore for the organism are called vestigial organs They are usually too small to be useful