CHANGES OVER TIME Unit Preview • Darwin’s Theory • Evidence of Evolution • The Fossil Record Darwin’s Theory • What important observations did Darwin make on his voyage? • What hypothesis did Darwin make to explain the differences between similar species? • How does natural selection lead to evolution? Key Terms Adaptation - A trait that helps an organism survive and reproduce. Evolution - The gradual change in a species over time. Fossil - The preserved remains or traces of an organism that lived in the past. Key Terms • Natural Selection - Individuals that are better adapted to their environment are more likely to survive. • Scientific Theory - A well-tested concept that explains a wide range of observations. • Species - A group of similar organisms that can mate with each other and produce offspring. • Variation - Any difference between individuals of the same species. Charles Darwin • A “naturalist” – studied the natural world. • Sailed on the Beagle to the Galapagos Islands. • Observed many unusual organisms on the island. – Giant tortoises – Blue-footed booby – Galapagos finches The Voyage of the Beagle • The Beagle made many stops along the coast of South America stopping at the Galapagos Islands. • Darwin observed living things as he traveled and tried to make connections about the relationships among those organisms. – Diversity of living things – Remains of ancient organisms – Unique characteristics of organisms on the Galapagos. Darwin’s Observations • The theory of EVOLUTION by NATURAL SELECTION • Evolution – The gradual change in a species over time. • Natural Selection – Individuals that are better adapted to their environment will survive and reproduce. DIVERSITY • The variety of life on Earth. • Darwin was amazed by the tremendous diversity of living things that he saw. • Scientists have identified more than 1.7 million species of organisms on Earth. FOSSILS • The preserved remains or traces of an organism that lived in the past. • Darwin was puzzled by some of the fossils he observed. • He saw fossil bones of animals that had died long ago but yet resembled the bones of organisms alive in Darwin’s time. Galapagos Organisms • Darwin observed many unusual life forms on these small islands. • He compared Galapagos organisms to organisms that lived elsewhere. • He also compared organisms on different islands in the Galapagos group. • He tried to make connections using the similarities and differences he observed. Comparisons to South American Organisms • The Galapagos organisms resembled many of those in South America. • Important differences between the organisms on the islands and those on the mainland were important in determining how the species ended up on the islands. • Darwin hypothesized that a small number of different plant and animal species had come to the Galapagos Islands from the mainland. – Blown out to sea during a storm – Set adrift on a fallen log • Once on the islands, the organisms reproduced and over time, their offspring became different from their mainland relatives because of their environment. IGUANAS • The iguanas on the Galapagos Islands had large claws. – Grip slippery rocks – Feed on seaweed • The iguanas on the mainland had smaller claws. – Climb trees – Eat leaves Comparisons Among the Islands • Darwin noticed many differences among organisms as he traveled from one island to the next. • Darwin was able to identify which island an organism came from just by looking at it. TORTOISES • Some had domeshaped shells. • Some had saddleshaped shells. • Tortoises lived inland and became like “land-dwelling mammals” grazing on vegetation. GALAPAGOS FINCHES • Each species was well ADAPTED (suited) to the life it led. • Beak shape was based on their diet. – Narrow, needle-like beaks = insects – Strong, wide beaks = seeds Adaptive Radiation • The evolutionary diversification of a single lineage into a variety of species with different adaptive properties. Theory of Evolution • Darwin spent 20 years consulting with other scientists, gathering more information, and reevaluating his observations from his trip on the Beagle before he developed his theory of evolution. • Plants or animals faced with different conditions will gradually change over many generations in order to become better adapted to their conditions. Selective Breeding • The process of selecting a few organisms with desired traits to serve as parents of the next generation. • By repeatedly allowing only organisms with the desired traits to reproduce, the more desirable trait becomes common and highly favorable in the offspring. • Darwin made connections between the practice of selective breeding and organism behavior in nature as evidence for his theory of evolution. Natural Selection • In 1858, Darwin proposed an explanation for how evolution could occur in nature. • Evolution occurs by means of NATURAL SELECTION. Natural selection is the process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other members of the same species. Factors Affecting the Process of Natural Selection • Overproduction • Variations • Competition • Selection • Environmental change • Genes OVERPRODUCTION • Most species produce far more offspring than can possibly survive. • A large number of offspring creates competition for resources. VARIATIONS • Members of a species differ from one another in many of their traits. • Variations are linked to environmental conditions. COMPETITION • Limited resources creates competition among members of a species. • Direct – Physical fights • Indirect – Searching for food – Avoiding predation SELECTION • Some variations make individuals better adapted to their environment. • Individuals who are better adapted survive and reproduce. • Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear. ENVIRONMENTAL CHANGE • A change in the environment can affect an organism’s ability to survive. • The environmental change can gradually lead to selection. • The Galapagos Islands are a prime example of how the environment can lead to the evolution of a species by natural selection. GENES • Without variations, all the members of a species would have the same traits. • Natural selection would not occur because all the individuals would have an equal chance of surviving and reproducing. • Variations can result from mutation and the shuffling of alleles during meiosis. • Genes are passed from parents to offspring. Natural Selection . . . . . . Survival of the Fittest!