Dichotomous

December 29, 2021

I was recently sent a link to the National Park Service web site addressing the use of dichotomous keys in species identification.  The sender knew I often struggled with a variety of identification tools to find what species I am blogging about.  The dichotomous key is a tool created to help scientists and the public identify objects and organisms.  Typically, a dichotomous key for identifying a particular type of object consists of a specific series of questions.  When one question is answered, the key directs the user to what question to ask next.  Dichotomous keys stress identifying species by their scientific name, as each individual species has a unique scientific name.  By contrast, common names for organisms often refer to many different species that may look like each other or share common characteristics.

When I looked the definition up online, I found the first known use of the English language word dichotomous occurred in 1752 and was used to refer to “dividing into two parts.”  The word is borrowed from the Late Latin “dichotomos,” which was borrowed from the Greek “dichótomos,”, meaning “cut in half, or divided equally.”  A dichotomous key then, is a key for the identification of organisms based on a series of choices between alternative characteristics.  The first known use of the phrase dichotomous key was 1889.  An example for using a dichotomous key in tree identification might ask whether the tree has leaves or needles.  The key then directs the user down one list of questions if the tree has leaves, and a different list of questions if it has needles.  This is like a questionnaire I just completed, where it stated, “If no, skip to question 3b.”

Dichotomous keys are useful because they allow non-expert users to identify organisms by directing them to look at known, important features.  Many people might not know how to distinguish different species of pine trees based on the arrangement of needles on a branch, but the key would be able to ask that question and give them useful information based on the result.  A dichotomous key arrives at the answer to species identification by presenting a series of questions with two possible answers.  Each answer given cuts down the list of possible candidate species by eliminating incorrect characteristics.  Dichotomous keys are useful to identify an organism as a member of a single, closely related group of organisms.  Complications may arise if multiple closely related species with similar characteristics live in the same geographic area.  Still, the key will get you closer to an identification than you were.

Thoughts:  The information on the National Park Service (NPS) site was part of a national program developed to educate children about the outdoors.  While this was online training, the NPS also offers in person education events, youth conservation corps, and young ranger internships.  This is part of the larger national education effort to train youth with skills in science, technology, engineering, and math, including computer science, collectively known as STEM/CS.  It is of growing importance to understand and solve the complex challenges of today and tomorrow, and literacy in STEM fields is essential.  This effort is designed to transcend where children live and provide access to quality learning environments.  If you do not build it, they will not come.  Follow the science.  Change is coming and it starts with you.