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How Does Evolution Work? Darwin showed us that species changed over time with his work on the HMS Beagle. BUT HOW DID THESE CHANGES OCCUR? Well, Darwin had a theory on how things evolved or changed over time.
EVOLUTION BY NATURAL SELECTION Darwin knew that dog breeders could select the traits they wanted in their dogs and breed them so the puppies would have the traits. A trait is a feature passed on from the parent to their offspring. Could nature select traits, too? Could nature somehow select the beaks of the finches Darwin saw? How could nature do that?
Which of these two foxes would survive the best in the arctic environment above? The key for Darwin was realizing that the organisms best suited to an environment were most likely to survive.
If you picked the white arctic fox you were right! The red fox would be easily seen in the white Arctic snow. It would be easy prey for a hungry predator. The process where organisms best suited for their environment survive and then go on to produce more offspring is called: NATURAL SELECTION
NATURAL SELECTION IN ACTION 1. The members of a species are all similar, but they are not exactly alike. You are similar to other members of your family, but you are not exactly the same, you each have some different traits.
NATURAL SELECTION The DNA you inherited from your parents determines most of your traits…whether you have brown hair or blond hair, blue eyes or brown eyes, light skin or dark skin.
MUTATIONS Some traits happen because of accidental changes in our DNA. These accidental changes are called mutations. Mutations can sometimes be helpful, producing new traits which help an organism to survive. The Panda has a mutation called the Panda’s Thumb. This is really an extra big wrist bone. The Panda eats a lot of bamboo, which is very hard to break and handle, and the thumb helps the Panda hold onto the bamboo.
NATURAL SELECTION 2. Organisms produce more offspring than can survive. Fish can lay millions of little eggs. Many of the eggs never hatch, some might be eaten by a predator, and others might not get the nourishment they need to survive.
NATURAL SELECTION 3. Some organisms will have traits that make them more likely to survive in their environment. These bugs have camofluage. Can you find them? After you have looked, right click to find the bugs. Traits that help an organism survive are called adaptive traits. Be sure to watch the Discovery Video in this lesson on some animal adaptations.
NATURAL SELECTION 4. The number of organisms that have adaptive traits increases in natural selection. Since the number of organisms with the adaptive traits live longer, they produce more offspring that have the adaptive trait. Click to watch the interactive tutorial http://www.techapps.net/interactives/mothproject.htm
NATURAL SELECTION 5. Species adapt to their environment. Things such as weather, food, and plant life all help species adapt. Think of the leaf bugs, who developed adaptations that allowed them to hide in the leaves in their habitat. Over time, some of the original species may become better and better adapted to their habitat. They become so much better adapted, that they can no longer mate with other groups of the species. They have become a brand new species. This is called SPECIATION.
Natural Selection is the process where organisms best suited for their environment survive and then go on to produce more offspring. SUMMARY SLIDE Organisms may be best suited for their environment because they have traits, either passed on from their parents or through an accidental mutation, that is helpful for their survival. Traits that help organisms survive are called adaptive traits and organisms with the adaptive trait tend to increase during natural selection because more survive.