Three reasons why dichotomous keys would be subject to changes over time

A dichotomous key is a rather large sequence of yes/no questions that result in identification of a living thing. This is important because of the level of separation it provides. A dichotomous key is a key that is used to classify a organism. It is like a list of criteria. Each criteria leads to another which will eventually narrow the number of possible species until you arrive at a specific one. A dichotomous key is used to categorize plants and animals. They are used when classifying a newly-discovered species. Categorizing new species is sometimes called 'keying out' the species.