Evolution
From Simple English Wikipedia, the free encyclopedia
Evolution is the theory (idea) that generations of organisms change slowly over time to be better able to live in their environment. A good 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 wouldn't use as much energy when flying for long periods of time (vultures), and some birds have adapted their wings simply to show off and make themselves appear larger (ostriches, peacocks). The scientist that came up with the theory of evolution was Charles Darwin.
These changes can happen very fast in simple organisms. For example, the bird flu epidemics that killed many people were caused by genetic changes in the virus that made the new viruses more deadly to humans.
[edit] Theory
The accepted theory of evolution is called natural selection. It works like this:
- Organisms will make 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 genetic.
- If these genetic differences help an organism survive and breed, they will be passed on to the next generation in larger numbers. If the genetic differences do not help an organism survive until it can breed, then those genetic differences will be lost.
- Over time, these genetic differences will accumulate until a new species has 'evolved'.
[edit] Types
There are two interesting ways we can see evolution in action - through convergent evolution and adaptive radiation.
Convergent evolution shows how unrelated organisms look similar because they have evolved from similar habitats. Dolphins, sharks, and ichthyosaurs all look very similar, but are not related at all. Evolution has shaped their bodies to look similar because they all lived in the ocean and swam quickly after fish.
Adaptive radiation shows how 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.
