A dichotomous key is a type of single-access key used in biology to identify an unknown plant or animal. It offers two choices at once and works best for closely related species. It can be adapted for use outside of biology, but may not always provide accurate results.
A dichotomous key is a type of single-access key that offers only two choices at once. These keys are commonly used in biology to identify an unknown animal or plant. To use these keys, the user determines which of two different choices is correct and then follows the key until a final choice eventually leads to the name of the organization. While it is possible to create a dichotomous key for any group of objects, they were originally created for use in biology and are most commonly seen in this field.
First used several hundred years ago, dichotomous keys are specially made to identify various life forms within a group. These keys work best when used to identify species that are closely related but have distinctive characteristics or behaviors that set them apart from other species in the group, such as the Galapagos Islands finches. While it is possible to create a dichotomous key for a large group, such as reptiles, the large number of species in this group makes it impractical for this type of use.
In a well-organized dichotomous key, the first pick will split the group into two groups that have roughly the same number of species each. Moving through the key will narrow the group down into smaller and smaller groups until some choices begin to identify individual species. They can be arranged linearly, which works well for small groups without many choices, or in branches.
It is possible to adapt a dichotomous key for use outside the biological sciences as well. Any group of different objects that require classification, such as stones or chemicals, can be identified using this type of key. Keys can also be created specifically for certain groups of things to eliminate extraneous choices that wouldn’t be in a given setting.
The problem with using a dichotomous key is that in some cases none of the choices will be true. The keys are based on information that is correct for most members of a species, or that is true in most cases, but may not be observed in a single specimen. For example, a choice that identifies the number of dots on a gecko’s tail as 5 or 7 may be impossible to answer if the gecko has lost its tail. In this case, it may be impossible to identify the creature correctly, or it may be necessary to follow multiple threads through the key, which can lead to confusion.
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