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Darwin’s Theory. What Was Darwin’s Hypothesis. In 1831, the British ship HMS Beagle set sail from England on a 5 year voyage around the world. On board that ship was Charles Darwin. Charles Darwin was a naturalist-a person who observes and studies the natural world.
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What Was Darwin’s Hypothesis • In 1831, the British ship HMS Beagle set sail from England on a 5 year voyage around the world. On board that ship was Charles Darwin. • Charles Darwin was a naturalist-a person who observes and studies the natural world.
What Was Darwin’s Hypothesis- Diversity • Darwin was amazed by the diversity of living things he saw during the voyage. • Wondered why were they so different than those in England. • Observed insects that looked like flowers, sloths, slow moving creatures that spent much of their time hanging in trees. • Today, Scientist know that organisms are even more diverse than Darwin thought. • In fact, scientist have discovered more than 1.6 million species on Earth. • The exact number of species is unknown because not all areas of our planet have been studied.
What Was Darwin’s Hypothesis-Fossils • Darwin saw fossils of organisms that had died long ago. • Darwin was puzzled when observing these fossils • He observed fossils that resembled the bones of living sloths but were much larger in size. • He wondered what had happened to the ancient , giant ground sloths.
What Was Darwin’s Hypothesis • Discussion • In Darwin’s day, people believed that all living things were created at the same time and that living things never changed. • Darwin’s observations led him to question these ideas. • What observations did Darwin make? • He noted the diversity of living things and the remains of ancient organisms.
Galápagos Organisms • The Beagle made many stops along the Atlantic and Pacific Coast of South America. From The Pacific coast, the Beagle then traveled to the Galápagos Islands. • He compared organisms from the Galápagos Islands to organisms that lived elsewhere. He also compared organisms living on the different islands.
Galápagos Organisms Compared to South American Organisms • Darwin discovered many similarities between Galápagos organisms and those found in South America. • Many of the birds and plants on the islands resembled those of the main land. • He also noted important differences between the organisms. • Example- You can see the differences between the island and main land iguanas.
Galápagos Organisms Compared to South American Organisms • Darwin became convinced that species do not stay the same. • Instead, he thought species could change and even make new species over time. • He began to think that maybe the island species were somehow related to the South American species. • Perhaps, he thought the island species had become different from their mainland relatives overtime.
Discussion • What kind of Comparisons did Darwin make on his voyage? • Compared Galápagos organisms to South American Organisms and he compared organisms along the Galápagos islands. • What did Darwin conclude from these observations? • The animals from the islands came from the mainland but had changed over time. • What did Darwin notice about the differences between species? • The differences increased the organisms ability to survive and reproduce in their particular environment.
Galápagos Comparisons among the Islands • Darwin also discovered many differences in organisms among the the different Galápagos Islands. • Tortoises on one island had dome-shaped shells while tortoises on an other island had saddle-shaped shells
Galápagos Organisms Adaptations • Birds were also different from one island to the next.
Galápagos Organisms Adaptations • When Darwin returned to England, he learned that the different birds were all finches. • Darwin concluded that the finch species were all related to a single ancestor species that came from the mainland. • Overtime, different finches developed different beak shapes and sizes that were well suited to the food that they ate. • Beak shape is an example of an adaptation. • Adaptation-a trait that increases an organisms ability to survive and reproduce.
Darwin’s Hypothesis • After the voyage, Darwin was convinced that organisms change over time.However, Darwin wanted to know how organisms change over time. • Over the next 20 years, he consulted with other scientist and gathered more information. • Based on his observations, Darwin reasoned that plants or animals that arrived on the Galápagos Islands faced conditions that were different than the conditions of the mainland. • Darwin hypothesized that species changed over many generation and become better adapted to new conditions.
Darwin’s Hypothesis • Darwin’s ideas are often referred to as the theory of evolution. • Scientific Theory- a well-supported and widely accepted explanation of nature. • From evidence collected, Darwin concluded that organisms on the Galápagos Islands had changed over time.
Discussion • What did Darwin believe led to the different adaptations in species on the Galápagos Islands? • The organisms that arrived on the islands faced conditions that were different from those on the mainland. Over many generations, the species became better adapted to the new conditions. • What did Darwin's ideas come to be known as? • The theory of evolution. • What is evolution? • The gradual change in a species overtime.
Darwin’s Hypothesis- Artificial Selection. • In artificial section, only organisms with a desired trait are bred. • Trait-a specific characteristic that an organism can pass to its offspring. • Darwin bred pigeons with large, fan shaped tails. By allowing only those pigeons with many tail feathers to mate, Darwin produced pigeon with two or three times the usual tail feathers. • Darwin thought that a process similar to artificial selection might happen in nature.
What Is Natural Selection? • Natural Selection-a 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. • Darwin identified factors that affect the process of natural selection: Overproduction, variation, and competition.
Overproduction • In many species, so many offspring are produced that there are not enough resources-food water and living space for all of them.
Variation • Members of a species differ from one another in many of their traits. • Variation-Any difference between individuals of the same species. • Example- Sea turtles may differ in color, size, the ability to swim quickly, and shell hardness
Competition • Since food, space, and other resources are limited, the members of a species must compete with one an other to survive. • Does not always involve physical fights between members of a species. Competition is usually indirect. • Example-some turtles may not find enough food to eat, a slower turtle may be caught by a predator, while a faster turtle may escape.
Selection • Individuals with variations that make them better adapted to their environment are more likely to survive and reproduce. • Their offspring may inherit the helpful characteristic. • The offspring in turn will be more likely to survive and reproduce and pass the characteristic to their offspring. • After many generations, more members of the species will have the helpful characteristic.
Natural Selection • In effect, the environment selects organisms with helpful traits to become parents of the next generations. • Darwin proposed that over a long time, natural selection can lead to change. Helpful variations can accumulate in a species, while unfavorable ones may disappear.
Darwin’s Theory Factors That Affect Natural Selection What are the factors of natural selection that affect a group of sea turtles over time?
Environmental Change • A change in the environment can affect on organisms ability to survive and therefore lead t natural selection.
Genes and Natural Selection • Without variations, all members of a species would have the same traits and the same chance of surviving and reproducing. • Where do variations come from? • Variations can result from changes in genes and the shuffling of different forms of genes when an egg and sperm join. • Genes, such as those for hair color and height are passed from parents to offspring.
