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Theory of Evolution
Charles Darwin
• Charles Robert Darwin
• Born February 12 1809 – April 19 1882)
• He was an English Naturalist
• He published his theory of evolution with evidence In his 1859 book “On the Origin of Species”.
The voyage of the Beagle
• In December 1831, the British ship HMS Beagle set sail from England on a five year trip around the world.
• Darwin was on board as a naturalist• His job was to learn as much as possible about
the living things he saw on the voyage.• Darwin's observations led him to develop one of
the most important scientific theories of all time; the theory of evolution by natural selection.
Darwin’s voyage
Darwin’s Observations
• Darwin made many observations along his stops on the Beagle
• Darwin's observations included the diversity of living things, the remains of ancient organisms, and the characteristics of organisms on the Galapagos Islands.
Darwin was amazed by the tremendous diversity of living things. Scientists now have identified more than 1.7 million species of organisms.
• A species is a group of similar organisms that can mate with each other and produce fertile offspring.
The Galapagos Islands• In 1835 the Beagle reached
the Galapagos Islands, where Darwin observed many unusual life forms on these small islands such as giant tortoises and giant iguanas.
• When Darwin returned to England, he compared organisms to organisms that lived elsewhere. He also compared organisms on different islands in the Galapagos group.
• He was surprised by some of the similarities and differences he saw.
• Darwin found many similarities between Galapagos organisms and those in South America. However, there were important differences.
• The Iguanas on the Islands had large claws that allowed them to grip slippery rocks while the iguanas on the mainland had smaller claws to climb trees.
• From his observations, Darwin hypothesized that a small number of plants and animals had come to the islands from the mainland.
• Once they reached the islands, the reproduced. Eventually their offspring became different from their mainland relatives.
Adaptations• Like the tortoises, the finches on the Galapagos
Islands were noticeably different from one island to the next.
• The most obvious difference on the Finches was their beak size and shape.
• Darwin proposed that each species of finch had a different size and shaped beak to suit its environment. This is an example of an Adaptation.
• An Adaptation is a trait that helps an organism survive and reproduce.
Evolution
• Darwin wanted to understand the different adaptations of organisms on the Galapagos Islands.
• He hypothesized that the species gradually changed over many generations and became better adapted to the new conditions.
• The gradual change in species over time is called EVOLUTION.
Natural Selection
• In 1858, Darwin and Alfred Russell Wallace, each proposed an explanation for how evolution could occur in nature.
• Darwin proposed that evolution could happen by 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.
• Darwin identified factors that affect Natural Selection:
• 1. Overproduction: Most species produce many more offspring that can possible survive.
• 2. Variations: any difference between individuals of the same species.
• 3. Competition: because resources are limited, members of a species must compete with each other to survive.
• 4. Selection: Darwin proposed that over a long time, natural selection can lead to change. Helpful variations may gradually accumulate in a species while the unfavorable ones disappear.
• 5. Environmental change: A change in the environment can affect the organisms ability to survive.
