Number of Species

Written by Jennifer Geer
Published: April 27, 2023
Image Credit © Julia Ardaran/


Scientists have estimated the number of species of plants and animals that currently exist on Earth to be around 8.7 million. However, this number is just an estimate as it is incredibly difficult to count the exact number.

What Is the Meaning of Species?

Scientists classify a species as a group of living organisms that can mate and reproduce, while members of a different species can not produce fertile offspring together. Also, members of the same species share similar physical and genetic characteristics with each other.

Why Don’t We Know the Exact Number of Species on Earth?

There are several reasons why it is difficult to answer the question of how many species exist. 

How we define species can get confusing. The problem with the definition ignores asexual animals and animals that interbreed. After all, it’s hard to have an exact count of species when biologists disagree on how to define the word species. 

For example, the definition of species states that organisms are in the same species if they can produce fertile offspring. However, this definition ignores asexual organisms, like hydras and Komodo dragons. It also ignores species that may interbreed, such as dogscoyotes, and wolves

Are Komodo dragons poisonous or dangerous
Female Komodo dragons can reproduce without the need for sperm, or assexually.


Life forms can be hard to find. Some species live in inaccessible habitats. Many living organisms live in places humans can’t reach, such as the deep sea. Or they are hard to find or too small to see. Scientists are still discovering creatures living in the depths of the ocean. 

For example, only in 2022, researchers observed for the first time a strange creature that looked to be a small pom-pom lying on the ocean floor. It turned out to be a spaghetti worm from the genus Biremis.

Tiny life forms, such as bacteria, are hard to count. It’s hard to count very tiny life forms. Some microorganisms can only be found by sequencing their DNA. And some species only live inside other animals. Parasites such as fungi, tapeworms, flukes, bacteria, and protozoa live inside the host animal.

Where Did the Number 8.7 Million Come From?

Because so many unknown life forms can’t be counted, scientists have to estimate the number of species. In 2011, scientists began using a technique using patterns to predict the number of species. This technique helped scientists to arrive at the number of 8.7 million, even though only 1.2 million species have been identified so far.

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About the Author

Jennifer is a professional writer living in the Chicago area. She owns two pugs. Or rather, they own her. Jennifer has discovered that her best writing happens against a backdrop of soft pug snores.