A dichotomous key is a type of chart that displays how something is classified. Dichotomous keys are often used within science when classifying plants or animals. These keys can also classify simple items like colors of people's names. Reading one of these keys is as simple as answering classifying questions before moving on to the next characteristic. Go through a dichotomous key one step at a time to get the most accurate answer.
Start at the end of the chart that has the broadest question or characteristic. You will continue through the key, like a map, by answering questions that get more and more specific until you get to the end of the chart with a specific answer.
Answer questions by following the line connecting the question to the previous answer. For example, if you were reading a simple chart on living things and wanted to classify the living thing as much as possible, you might start at the top with a choice between plant or animal.
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Answer the question: "Are humans plants or animals?" You would then choose an answer based on the question. Humans are animals.
Move down the chart to follow the "animals" line until you hit another set of classifications. You might come to two choices "invertebrates," which are animals without a backbone, or "vertebrates," which are animals with a backbone. Since humans have a backbone, choose "vertebrates" and follow that line down to the next set of classifications.
Read the next set of choices, which may have items like "fish," "mammals," "birds," "reptiles," etc. Pick a choice that humans would fall under. Since humans are mammals, pick "mammals" and follow the line to the next series of classifications.
Go through your next choices, which might include "seals," "marsupials," "primates," and "whales and dolphins." Since humans fall under the category of "primates," follow that choice, which will answer the question you started with, "What family do humans fall under?" Humans fall under the "primate family."
Use this method when reading other dichotomous keys.