Darwin • Darwin’s journey around the Galapagos Islands lead him to introduce the theory of Natural Selection. • As Darwin visited the Islands, he carefully documented and collected evidence to support his findings.
Evidence • Darwin’s most important findings came from fossils, geography, embryology, and anatomy.
Fossils • Fossils are preserved remains or traces of animals. • Early scientists discovered that fossils differed from each other depending on which rock layer (strata) they were found in.
The fossil organisms found in the bottom layers were more primitive (simple) than the fossil organisms found in the top layers. • The fossil record supported Darwin’s theory of natural selection.
Darwin found many fossil records that looked similar to present organisms but had distinctly different features. This suggested that organisms changed gradually overtime. • Darwin concluded that the world would have to be older than 6000 years (which was the common belief at the time) in order for the organisms to have evolved that drastically.
Geography • During Darwin’s time on the Beagle, he noticed that the animals on the islands were very similar to the animals on the mainland, yet the animals on each island were adapted to the environment of each of their islands.
Darwin hypothesised that the animals on the islands migrated to the islands. • Different climates, predators, and plants, favoured different traits in the migrants.
Overtime, the specific traits became well established since the islands were too far away from each other to have mating occur.
Embryology • Many embryos of vertebrates are very similar to each other. For example birds, reptiles, fish, and mammals all have gill slits as embryos.
Similar features in embryos in very different organisms, provides evidence for a common ancestor.
Anatomy • Darwin spent much of his time observing physical structures of animals. • Homologous Structures: are features that are similar in structure but appear in different organisms and have different functions.
Homologous structures provide more evidence for a common ancestor. • Having similar structures does not mean that two animals are related to each other, just that they have a distant common ancestor.
Analogous Structures: are structures that perform similar functions, but do not have the same origin. • An example is the wings bats and insects. Both function in flight, however, a bat is a mammal, while an insect is an arthropod.
Their ancestors must have faced the same environmental challenges, so they came up with the same solution, however, they are NOT related.
Vestigial Structures: are remnants of organs or structures that had a function in an earlier ancestor, but no longer have a use. • Examples of vestigial structures are the appendix in humans, the wings of ostriches, and the pelvic bone of snakes.
Over LONG periods of time vestigial structures become smaller as they are no longer used. • Vestigial structures are very important in providing evidence of how evolution occurs.