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Lesson 6-2 The Theory of Evolution by Natural Selection Darwin’s Voyage Charles Darwin served as a naturalist aboard the HMS Beagle. A naturalist is someone who studies plants and animals by observing them. One of the highlights of Darwin’s voyage were the Galapagos Islands west of South America. Darwin noticed different varieties of tortoise, finch, and mockingbird on each island. Some were different enough to be separate species. Darwin’s Voyage Galapagos Tortoises Darwin noticed there was a relationship between each species and the food sources of the island it lived on. The species of tortoise living on islands with taller plants had longer necks. The species of tortoise living on islands with shorter plants had shorter necks. Darwin concluded all of the Galapagos tortoises shared an ancient common ancestor. Galapagos Tortoise Darwin’s Finches Darwin noticed that finches on the islands had beaks that matched their primary food source. Finches that ate mostly insects had shorter, pointier beaks. Finches that ate mostly large seeds had bigger, more powerful beaks. Darwin’s Finches Darwin’s Theory Darwin spent many years studying notes and specimens from the Galapagos Islands. He realized that variations in populations could help explain how different species on the Galapagos evolved. Variations are slight differences within members of a species. Populations are groups of individuals from the same species living in the same area. Natural Selection Darwin’s experiences with the Galapagos led him to develop the theory of evolution by natural selection. Natural selection is the process by which the best adapted individuals in a population become most likely to survive and reproduce. It predicts that species will develop adaptations that match their environment over time. Natural selection is driven by four main factors. Natural Selection 1. Limited resources mean parents produce more offspring than can survive. 2. Members of a species must compete for resources. 3. Helpful variations give some individuals an advantage in the competition for survival. 4. Survivors reproduce and pass on their traits to offspring. Adaptation An adaptation is a characteristic of a species that helps the species survive in its environment. There are three main categories of adaptation: Structural Behavioral Functional Adaptation Structural adaptations involve shape, size, color, and other physical features. Example: A bird’s wing. Behavioral adaptations involve actions. Example: A tiger hunting. Functional adaptations involve internal body systems. Example: Expanding blood vessel’s in a rabbits ear to cool off. Specialty Adaptations Camouflage is a structural adaptation that aids members of a species with blending in with their environment. Example: An owl that looks like tree bark. Mimicry is an adaptation in which one species resembles another species. Example: Some flies are striped like bees. Camouflage Mimicry Artificial Selection Selective breeding is the breeding of organisms by humans for desired traits. Example: Dog breeds are bred to have a certain size, color, or behavior. Since humans are choosing traits instead of nature, selective breeding is also called artificial selection. Artificial Selection