One Frog Species Turned Out to Be Six or Seven. Scientists Say Billions More May Be Hiding.

For nearly two centuries, a small brown frog living in Southeast Asian rainforests was considered a single, well-understood species. It had a name. It had a place in the textbooks. Case closed.

Then modern genetic sequencing cracked it open again. That one familiar frog is turning out to be six or seven distinct species—a finding that raises a compelling question: How many of Earth’s creatures have been hiding in plain sight?

Discovery looks different now

The popular image of species discovery involves an explorer stumbling across something never before seen. The modern reality is more methodical than that.

Chan Kin Onn, a herpetologist at Michigan State University who has spent years studying amphibians and reptiles in Southeast Asia, said the popular image doesn’t match the process. “Most people have this image of an intrepid explorer braving an isolated mountain or some other remote place, and stumbling across a creature that no one has ever seen before,” Chan said. “But most of the time it’s far less glamorous.”

Many new vertebrate species are identified by revisiting known populations and using improved data and technology to determine whether they are more genetically distinct than previously understood. Less stumbling upon a new animal, more looking at a familiar one through a powerful new lens—and realizing it’s been keeping secrets.

The Bornean fanged frogs

Chan’s research focuses on a group of small brown frogs from Southeast Asia known as Bornean fanged frogs, named for tooth-like projections on their jaws. One species in the group, Limnonectes kuhlii, has been recognized by science since 1838. For generations, it was treated as a single, widespread species.

Genetic studies over the past two decades began to suggest something different: the frogs might represent as many as 18 species rather than one.

Chan and colleagues analyzed DNA from frog specimens collected across the mountain rainforests of Malaysian Borneo, examining more than 13,000 genes across the frogs’ genomes. According to the study, published Jan. 14 in the journal Systematic Biology, the frogs fall into multiple genetic clusters. The researchers concluded that only six or seven of those clusters qualify as distinct species.

“It’s not just one species. But it’s not 18 species, either,” Chan said.

Cryptic species: identical to the eye, different in their DNA

The frogs belong to a category scientists call cryptic species—animals that look nearly identical to one another but are genetically distinct. They’ve been quietly evolving along separate paths, even though human eyes can’t easily tell the difference.

“Animals that look similar but are genetically distinct are called cryptic species,” Chan said, noting that advances in genetic sequencing have accelerated discoveries of these hidden species.

Chan noted that there are more than 9,000 amphibian species worldwide, with roughly 100 to 200 new species added each year. Many of these additions are cryptic species, creatures already sitting in museum collections or well-known habitats, waiting for someone with the right tools to notice they’re not quite what they seem.

Species don’t emerge all at once

Perhaps the most thought-provoking finding from this research challenges a common assumption: that species emerge as clear, neatly separated categories.

The researchers detected significant interbreeding between the frogs. “We found a ton of gene flow going on,” Chan said. Because genetic material moves between populations, the boundaries between potential species can become blurred. Chan said some proposed cryptic species may reflect differences in scientific methods rather than clear biological divisions.

“It’s not like all of a sudden, boom. It’s more of a continuum,” Chan said.

“This study shows that there’s a speciation ‘gray zone’ that can make it hard to draw the line,” Chan said.

That idea—speciation as a gradual process rather than a sudden event—means the tree of life isn’t a tidy diagram with crisp branches. It’s something messier, more fluid.

So how many species are really out there?

Similar genetic studies across animals, including insects, fish, birds and mammals, suggest that many species could still be undiscovered. Earlier estimates suggested Earth contained about 8.7 million species. Newer models that account for cryptic species indicate the total number could be anywhere from seven to 250 times higher.

If the higher estimates hold, the true number of species on Earth could be in the billions.

What this means for conservation

The findings carry weight beyond academic classification. A 2023 global study of roughly 8,000 amphibian species found that two out of five amphibian species are threatened with extinction, making them the most endangered group of vertebrates.

“There are so many species in the world that we still haven’t discovered, and that could go extinct before we can give them a name,” Chan said.

He also cautioned that splitting species too aggressively can complicate conservation decisions. “We cannot possibly conserve everything, so we have to triage and decide how to allocate limited resources toward what we think are the highest priorities,” Chan said. “We could be putting names on things that shouldn’t be prioritized.”

It’s a difficult balancing act: identifying the full scope of life on Earth while making hard choices about which species receive protection.

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This story was originally published March 6, 2026 at 2:28 PM.