Download Natural Selection - Field Natural History - Lecture Notes and more Study notes History in PDF only on Docsity! Field Natural History Natural Selection and Evolutionary Patterns I. CHANGE, EVOLUTION AND CHANCE A. The world is a changing place. Organisms change in time in response to their environment. Sometimes these changes take place of over millions of years. 1. The development of different species from an earlier, ancestral species is known as divergent evolution. 2. Example of modern day horse, Equus, a descendant of Hyracotherium that was present around 54 million years ago. 3. Hyracotherium was very successful, but as the environment changed and became drier, other variations on Hyracotherium were more successful. B. A rapid increase in the number of different, but closely related species is known as adaptive radiation. This can occur under two circumstances. 1. When an organism invades a previously unexploited environment. Example 1: It is thought that the diversity of finches that Darwin discovered on the Galapagos islands were the result of adaptive radiation from one individual that found its way to the islands from the mainland of South America. a. Each finch has exploited a way of making a living – a niche that was not previously occupied. Example 2: Evolution of wings allowed insects to enter a new adaptive zone. a. Adaptive zone is broader than a niche; it represents a completely new way of life. In this case, life in the air. 2. The other manner in which adaptive radiation occurs is when a group of organisms evolve a set of characteristics that make them more successful under the current environmental conditions. a. Reptiles eclipsed dominance of amphibians on land. b. Reptiles possess traits that allow them to be less dependent upon water. c. Reptiles displace amphibians. C. Extinction is an important part of evolution. 1. Extinct species were successful in their environment at one time – but the environment changed, and they did not survive. 2. The extinction of large groups of animals can pave the way for adaptive radiations. D. Organisms that have developed similar solutions to living in a particular environment are not necessarily related. 1. When organisms with widely different backgrounds arrive at the same solution to a similar environmental demand (flying, swimming), it is called convergent evolution. 2. When similar structures are derived from unrelated parts, they are called analogous structures. Docsity.com
