# How many animals exist on Earth: the first study to count them

#### Calculating the number of living animals on our planet is more difficult than expected and scientists have prepared a new theory to explain why

It's a question scientists have been asking for centuries: how many animals exist on Earth? Until now, only rough estimates have been made, and professors in Syracuse University's College of Arts and Sciences have been trying to figure out if the scientific community will ever be able to establish a "total number" of living vertebrate species. This discovery has many benefits and could help in the conservation of species and prioritize what needs to be done.

The two researchers Bruce Wilkinson and Linda Ivany, both from the Department of Earth and Environmental Sciences, published an article in the Biological Journal of the Linnean Society where they came to the conclusion that predicting the total number of species may never be possible.

Only a fraction of the currently existing species, in fact, have been given a name and new species are discovered every year. Therefore, scientists can only try to make a prediction about the number of species that may someday be found.

#### A "bell-shaped" curve to find out how many animals live on Earth

To determine how many total animals there are on the planet, geologist Bruce Wilkinson explained that the number of discoveries over time follows a bell-shaped curve: the curve rises when the rate of production increases due to new discoveries and then falls when production decreases.

"The problem with using that curve," the geologist explained, "is that you have to assume that the effort invested and the approach used to discover a new species is consistent and known."

To give an example, if researchers had estimated the total number of species based on pre-1950 data, the numbers would be very different than they are today and would be wrong.
"As much as we'd like to know 'the number' of animals on Earth, the total species richness of the planet will remain an elusive goal," concluded researcher Linda Ivany.

How many species of animals live on our planet, then? According to the most recent estimates, the number is around 8 million but, in fact, every year new discoveries are added and at the current rate it is estimated that it will take at least another 400 years to discover them all.

Armando Mercuri