Roughly three centuries ago, Swedish naturalist Carl Linnaeus set out to catalog and name every living organism he could find. He is now widely regarded as the founder of modern taxonomy after introducing the binomial naming system and formally describing more than 10,000 species of plants and animals. Scientists have continued that mission ever since, steadily expanding humanity's understanding of Earth's biodiversity.

A new study led by researchers at the University of Arizona and published in Science Advances shows that the pace of discovery is accelerating. Today, scientists are identifying more than 16,000 new species each year, the highest rate ever recorded. The researchers say this trend is not slowing and suggest that groups such as plants, fungi, arachnids, fishes and amphibians are far more diverse than previously believed.

"Some scientists have suggested that the pace of new species descriptions has slowed down and that this indicates that we are running out of new species to discover, but our results show the opposite," said John Wiens, a professor in the University of Arizona Department of Ecology and Evolutionary Biology, in the College of Science, and senior author of the paper. "In fact, we're finding new species at a faster rate than ever before."

What the Data Reveal About Global Biodiversity

To reach their conclusions, the team examined the taxonomic records of roughly 2 million species from across all major forms of life. Looking at the most recent period with comprehensive data, between 2015 and 2020, they found that researchers documented an average of more than 16,000 new species per year. These discoveries included more than 10,000 animals (dominated by arthropods and insects), about 2,500 plants, and roughly 2,000 fungi.

"Our good news is that this rate of new species discovery far outpaces the rate of species extinctions, which we calculated to about 10 per year," said Wiens, referring to another study he led that was published in October. "These thousands of newly found species each year are not just microscopic organisms, but include insects, plants, fungi and even hundreds of new vertebrates."

More Species Than Ever and Many Still Undiscovered

Wiens and his co-authors found that scientists are describing more species annually than at any other time in history. They also used long-term trends in discovery rates to estimate how many species may exist overall. Their projections suggest there could be as many as 115,000 fish species and 41,000 amphibian species, compared with about 42,000 fish and 9,000 amphibians currently described. The researchers also estimate that the total number of plant species could exceed half a million.

"As the famous ecologist Robert May said, if visiting aliens asked us how many species live on our planet, we would have no definitive answer," said Wiens. "Right now, we know of about 2.5 million species, but the true number may be in the tens or hundreds of millions or even the low billions."