The Sixth Mass Extinction Hasn’t Started Yet

It’s fashionable to declare that we’re in the middle of a mass extinction, but the numbers tell a more complicated story. A new study published in PLOS Biology finds that while species are disappearing at an alarming pace, the losses at higher taxonomic levels, such as genera, remain surprisingly sparse. That distinction matters.

Biologists John Wiens of the University of Arizona and Kristen Saban of Harvard University examined data from more than 22,000 plant and animal genera assessed by the International Union for Conservation of Nature (IUCN). Since the year 1500, they found 102 genera had vanished—less than 0.5 percent of those evaluated. That is a fraction compared to the broad collapses seen during the five true mass extinctions in Earth’s past, which erased entire families and orders.

Most of these genus-level losses were concentrated among birds and mammals, and three-quarters came from island endemics—creatures hemmed in by isolation and highly vulnerable to invasive predators. The timing also cuts against the common narrative of acceleration. Extinction rates at the genus level peaked in the late 1800s and early 1900s, then slowed rather than sped up across the past century.

Wiens was blunt in his assessment.

“We found instead that extinctions of genera are very rare across plants and animals, that they were mostly of genera found only on islands, and that these extinctions actually slowed down over the last 100 years instead of rapidly accelerating,” he said.

The paper also pushes back against an influential 2023 study that framed recent genus extinctions as a signal of an unfolding mass extinction threatening human survival. Wiens and Saban argue that link was overstated. Extinctions on small islands, while devastating for local ecosystems, are unlikely to “destroy the conditions that make human life possible.”

That doesn’t mean the biodiversity crisis has been exaggerated. Hundreds of species have been lost in the past five centuries, and countless more are teetering. The real risk is cumulative: the thinning out of specialized roles within ecosystems, the steady decline in genetic diversity, the quiet hollowing of resilience. But as this new analysis makes clear, the collapse of whole branches of the evolutionary tree has not yet begun.

Saban underscored another point—accuracy matters when communicating conservation science.

“Now more than ever, given the widespread mistrust in science, it is important that we conduct conservation research carefully and present it accurately,” she noted.

This raises an uncomfortable but necessary tension in conservation rhetoric. Alarm helps capture public attention and mobilize resources, but exaggeration risks backlash. The researchers argue that preventing extinctions is justified on moral grounds alone—humanity does not need to frame every vanishing species as an existential threat to itself. The moral wrongness of wiping out other forms of life should be enough.

And yet, one wonders: if the true crisis is slower, patchier, and less cinematic than past mass extinctions, will the world muster the urgency to act? For now, the fossil record of the future is still unwritten.

A “mass extinction” is defined not just by how many species die out, but by the collapse of larger branches of the evolutionary tree—genera, families, and orders. These higher taxonomic levels represent entire clusters of diversity and ecological function. In the five past mass extinctions, more than 75% of species and many higher groups disappeared. By contrast, since 1500, fewer than 0.5% of genera have gone extinct. While species losses are serious, the current crisis has not yet reached the taxonomic breadth of a true mass extinction.

Journal: PLOS Biology
DOI: 10.1371/journal.pbio.3003356