Chapter 15

Evolution – any change over time Theory – testable explanation that is well supported 1831 – Charles Darwin’s voyage aboard the H.M.S. Beagle allowed him to make observations from around the world. Began to realize that there were many more species than originally thought. Similar environment did not mean similar animals. Also collected fossils (preserved remains of ancient organisms) that were similar to but still different from present day organisms Others were completely different

Galapagos Islands – animals differed greatly from island to island Ex. Shape of tortoise shells Ex. Beak shape of finches

Geology At this time most thought the Earth was only a few thousand years old – James Hutton – Earth is shaped by geological forces that took place over extremely long periods of time 1833 – Charles Lyell – processes occurring now have shaped Earth’s geological features over long periods of time These ideas made the Earth much older than thought. These two ideas made Darwin consider that life may change as well over long time periods.

1 st Theory of Evolution 1809 – Jean-Baptiste Lamarck By selective use or disuse of organs, organisms gained or lost traits during their lifetime and passed these traits on to their offspring. Ex. A giraffe stretches its neck to reach higher leaves. It then passes on a longer neck to its offspring. Now know this is not true. Inherited genes pass down traits.

Population Growth 1798 – Thomas Malthus – human population grows faster than space or food supplies Darwin realized this applied to all organisms, not just humans. Led him to question what factors determine which ones survive and reproduce.

Natural Selection 1858 – Alfred Wallace – sent an essay to Darwin about evolutionary change This motivated Darwin to publish his own work 1859 – Darwin published On the Origin of Species Proposed the idea of Natural Selection Natural variation is found in every species. Artificial selection – humans choose the natural variation that we found useful

Natural Selection cont. Natural Selection Every organism has a struggle for existence. Survival of the fittest – those individuals with adaptations that enable fitness survive and reproduce most successfully Fitness – ability to survive and reproduce in a specific environment Adaptation – inherited characteristic that increases an organism’s chance of survival Descent with modification – over time natural selection produces organisms with different structures Each living species has descended, with changes. Common descent – all living things were derived from a common ancestor

Evidence of Evolution Fossil record Compare fossils of different ages to see how life has changed. Geographic distribution Animals adapt to their environment. Convergent evolution – animals with different ancestors become similar due to similar environments Divergent evolution – animals with a common ancestor become different due to different environments

Evidence of evolution cont. Comparative anatomy Homologous structures – structures with similar forms but different functions Ex. Human arm, bat wing, whale flipper Vestigial structures – structures that no longer have a function Ex. Appendix, pelvic girdle in snakes Embryology Comparing the embryos of organisms Tails and gills are present in most