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Learn about the theory of evolution and natural selection proposed by Charles Darwin, including his observations from the Galapagos Islands and evidence of evolution in fossils.
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Evolution • Evolution is the gradual change of a species over many generations. • Evolution is a theory. A scientific theory is a well-tested concept that explains a wide range of observations. • Hypothesis – an educated guess, a possible explanation for a set of observations or answer to scientific questions; must be testable. • Law - A scientific law is a statement that describes, predicts, and perhaps explains why a wide range of phenomena behave as they do in nature. (Newton’s laws of motion or the law of gravity)
Charles Darwin • Naturalist, Charles Darwin, was born in England, on February 12, 1809. • In 1831, he embarked on a five-year voyage around the world on the HMS Beagle. • His studies of specimens around the globe led him to formulate his theory of evolution and his views on the process of natural selection. • In 1859, he published The Origin of the Species by Means of Natural Selection. • He died on April 19, 1882, in London.
What is Natural Selection? • In Darwin’s book The Origin of Species, he explained that 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 species. • Species – a group of similar organisms that can mate with each other and produce fertile offspring. A mule is not a species because they are not fertile and cannot mate with each other. Mules can only be produced by breeding a male donkey and a female horse. • Adaptations – Traits that help an organism survive and reproduce. (wings, claws, teeth, camouflage, venom, speed and mimicry just to name a few)
Galapagos • One interesting place that Darwin visited was the Galapagos Islands. • These islands are located about 600 miles from Ecuador, South America. • Darwin noticed that the plants and animals on these islands were similar to those in Ecuador, but not exactly the same.
Giant Tortoise Blue-Footed Booby Frigate Bird Seal Sally Light-Foot Crab Iguana
Darwin’s Finches Darwin observed that the finches on the islands were different from those in Ecuador. Their beaks were adapted according to how they obtained their food. Beak shape is an adaptation that helps the finches survive.
Darwin observed that other animals on the islands were similar to the mainland animals, but there were some important difference. For example the iguanas on the islands had long, large claws for gripping rocks and eating seaweed. The iguanas on the mainland had smaller claws for climbing trees and eating leaves. He also observed large sea birds called cormorants that lived in both places. The mainland cormorants could fly, but the island birds could not.
The tortoise on the islands had a dome shaped shell and the mainland tortoise had a saddle shaped shell. • Darwin inferred that the plants and animal from the mainland, were possibly blown to the islands by a storm. • Over time their offspring became different from their mainland relatives. • The island species had to adapt to survive in their new environment.
Darwin’s Theory of natural Selection • Darwin knew that people used selective breeding to produce crops and animals with desired traits. • Darwin thought that a process similar to selective breeding must happen in nature. • Darwin identified a number of factors that affected the process of natural selection: Competition • Overpopulation • Darwin observed that many species produce more offspring than can possibly survive. So many offspring are produced that there is not enough resources – food, water, and living space – for all of them. • Example • Each year a female sea turtle may lay more than 100 eggs. Some of the eggs will survive and develop into adult turtles, and some will not.
Struggle to Survive • Some sea turtle may be caught by predators, and some may starve or get a disease. Only some of the turtles will survive • Inherited Variation • Every individual organism has it own combination of inherited traits. Each organism is similar to, but not identical to, its parents. Over along period of time , natural selection can lead to evolution. Helpful variations gradually accumulate in a species, while unfavorable ones disappear. • Successful Reproduction • The sea turtles that are best adapted to their environment are likely to have offspring that survive.
Evidence of Evolution • Evidence that organisms have evolved is buried within the Earth's crust. • Fossils – the remains or imprints of once-living organisms that are found in layers of rock and sediment. • The dead organism is covered by a layer of sediment , and over time minerals in the sediment seep into the organism and gradually replace the organism with stone. • If the organism rots away completely after being covered, it may leave an imprint of itself in the rock.
Evidence of Ancestry • Fossil Record – is a timeline that gives the order in which species have existed. • Fossil near the bottom are the oldest and fossils near the top are more recent. • Scientist observed that all living things have characteristics in common. They think that all living species descended from common ancestors.
Branching Trees - are diagrams that imply or infer that species have descended from a common ancestor. Scientists use information about these species to sketch out a “tree of life” that includes all known organisms.
Homologous Structures Homologous structures provide evidence that these four organisms have all evolved from a common ancestor. Notice that the bones in the forelimbs of these four animals are arranged in a similar way.
Embryology • During the early stages of development all eight of the organisms have a tail and tiny gill slits in their throats. These similarities suggest that these vertebrate species are related and share a common ancestor.
DNA • Scientist infer that species inherited many of the same genes from common ancestors. Techniques have been developed that allow scientist to extract DNA from fossil bones, teeth and from insects trapped in amber.
