| Overview |
| The goal of life forms is to reproduce. |
| Reproduction with variation creates variety. |
| Some varieties of life survive better. |
| Some of these life forms produce more offspring. |
| Some differences are passed on to offspring. |
| Over time new species result. |
| This story, forming the history of life on the planet, is recorded in fossils. |
Evolution is the term used to describe the change of organisms over generations.
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In a general way, evolution is described as the changes that have transformed life from its earliest origins into the diverse forms of life represented today. More specifically, the Scientific Theory of Evolution states that all living things share, at some point in their evolutionary history, a common ancestor. Evolution depicts life as a tree, with many branches arising from a single trunk. The tips of the branches represent present-day life forms. Each fork in the branch represents ancestors common to all lines arising after the split.
The idea of common ancestry has its roots in the Darwinian revolution. Charles Darwin saw unity among all life, and he proposed that all living things are related and have descended from a common ancestor. Darwin describes these events as descent with modification. The Darwinian explanation for the mechanisms of evolution is based on his theory of natural selection, which in turn is based on five basic ideas:
- - Organisms will produce more offspring than their habitat can sustain. There will be a 'struggle to survive'.
- - Not all the offspring will be identical.
- - Some of the differences between the offspring will be due to variations in their genetic makeup.
- - Genetic variations that allow an organism to survive and reproduce will be passed on to the next generation. Genetic variations that do not help an organism to survive and reproduce will be lost.
- - Over time, these genetic variations will accumulate until a new species results.
Modern Synthesis / Population Genetics
Evidence For Evolution
Fossil Record
Comparative Anatomy
Artificial Selection
Molecular Biology
Evolution in action
Ways we can see evolution in action include convergent evolution and adaptive radiation.
Convergent evolution results in unrelated organisms looking similar because they have evolved to survive in similar habitats. Dolphins, sharks, and ichthyosaurs all look very similar, but are not at all closely related. One is a mammal, one a fish, and one a reptile, but evolution has shaped their bodies to look similar because they all lived in the ocean and swam quickly after fish.
Adaptive radiation means that a single part of the body can be re-shaped to be used in different ways. A good example of this is the hand of a mammal. Bats, humans, whales, and cats all have very different looking hands, but they are all made up of similar patterns of bones. Another example is the wing of a bird. Over time some birds' wings evolved into more of a flipper, so that they were better suited for swimming (penguins). Some birds' wings evolved for soaring, so that they would not use as much energy when flying for long periods of time (vultures), and some birds' wings have been adapted simply for showing off and making the bird appear larger (ostriches).
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