Evolution. Darwin s Voyage.

Transcription

1 Evolution Darwin s Voyage

2 Charles Darwin n Was a naturalist a person who studies the natural world. n In 1831 the British naval ship HMS Beagle set sail from England on a five year long trip around the world. n Darwin s job was to learn as much as he could about the living things he saw on the voyage

3 Darwin s Voyage

4 n Darwin observed plants and animals he never seen before and wondered why they were so different from those in England. n His observations lead to the most important scientific theories of all time: the theory of evolution by natural selection.

5 Darwin s Observations n Scientists now have identified more than 2.5 million species of organisms on Earth. n A species is a group of similar organisms that can mate with each other and produce fertile offspring. n Darwin observed new plants and animals at each stop in the voyage. He also observed bones of animals that died long ago. n In 1835 the Beagle reached the Galapagos Islands and he observed some of the greatest diversity in life forms.

6 Similarities and Differences n Although Darwin was surprised at how different the plants and animals were he also noted some similarities. (how they were the same) n Both places had cormorants, for example, however they did not fly on the island.

7 n The iguanas on the islands had large claws that allowed them to keep their grip on slippery rocks and fed on seaweed. n The iguanas on the mainland had smaller claws and ate leaves.

8 n He also noticed difference among organism from one island to the next. n For example, one tortoise had dome-shaped shells and on another island the tortoise had a saddleshaped shell.

9 Darwin inferred: n A small number of different plant and animal species had come to the Islands from the mainland n They might have been blown out during a storm or set adrift on a fallen log. n Once on the island they reproduced n Eventually, their offspring began to change

10 Adaptations n Finches varied from island to island, in size and shape of their beaks n Finches that ate insects had sharp, needlelike beaks n Finches that ate seeds had strong, wide beaks. n Beak shape is an example of an adaptation, a trait that helps an organism survive and reproduce

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12 Evolution n Darwin spent 20 years going over observations with other scientists n From observations, he concluded that species gradually changed over many generations and become better adapted to the new conditions. n The gradual change in a species over time is called evolution.

13 n Darwin s ideas are often referred to as the theory of evolution. n A scientific theory is a well-tested concept that explains a wide range of observations. n Darwin knew that evolution had occurred on the Galapagos Islands, but he did not know how it happened.

14 Natural Selection n The Origin of Species Darwin s book that explained natural selection and evolution. n Natural Selection 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. n Factors that affect it are: overproduction, competition, variations and selection.

15 Factors that affect Natural Selection Overproduction Competition Selection Variations

16 n Overproduction Most species produce many more offspring than can possibly survive. In these species there is not enough resources for all to survive. n Example: Sea turtles lay more than 100 eggs n Competition - Since food and other resources are limited, offspring have to compete with each other to survive. n Variations- Any difference between a species is called a variation.

17 n Some variations make certain individuals better adapted to their environment. n Those individuals are more likely to survive and reproduce. n Over a long period of time, natural selection can lead to evolution. n Helpful variations gradually accumulate in a species, while unfavorable one disappear.