Species Identification

When Linnaeus developed his system of species classification, scientists had little more than visual observation of physical characteristics on which to base their taxonomy. Today, scientists have many more tools at their disposal, allowing them to modify classification systems based on new information gathered. For example, scientists can compare the biochemistry and developmental stages of organisms. They can also examine and interpret the fossil record.

 

Molecular Clocks

The DNA of an organism changes slightly each time it is passed from one generation to the next. These changes are called mutations, and they can cause amino acid substitutions in proteins. Because mutations tend to occur at a constant rate over time, they can be used to measure evolutionary time. A molecular clock is a model that uses mutation rates to estimate the length of time that has passed since an organism has diverged from its ancestor. In this interactivity, you will learn more about what molecular clocks can tell us about evolutionary relationships. Click the player button to begin.

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Similarities Across Diverse Organisms

When you look at your arms, would you believe that many other mammals, reptiles, and amphibians have the same bones in their limbs? This may be hard to believe since a bird, for example, uses its limbs for flight and a whale uses fins to swim through water. However, even though these bones move differently, they have the same origin. In this interactivity, take a moment to learn more about similarities across diverse organisms. Click the player button to begin.

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Species Identification Review

Now that you have explored molecular clocks, homologous structures, and embryonice development, it is time to review your knowledge and practice what you have learned. In this non-graded activity, read the questions or statements and select the appropriate answers. Click the player button to get started.