Portugal's ancient giant bears shrank over thousands of years and humans may be to blame
About 22,000 years ago, a giant brown bear lumbered across what is now Portugal. The creature weighed around 385 kg (about 850 pounds), making it one of the largest of its kind ever found, towering over the Iberian brown bears that live there today.
The bear is one of several surprises researchers uncovered during an analysis of hundreds of ancient bear bones from caves across Portugal. Their study, published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, reveals that Iberian brown bears were once colossi that have since lost nearly half their bulk, a trend researchers say is due to thousands of years of evolution linked to environmental pressure and human hunting.
"Nothing in biology makes sense without the light of evolution," said study lead author Darío Estraviz-López, a paleontologist at the NOVA School of Science and Technology in Portugal, quoting evolutionary biologist Theodosius Dobzhansky. Paleontology, he said, is one of the best tools we have for understanding how a species got to be the way it is. But what can it tell us about Portugal's once-giant brown bears, and why did they shrink?
No cave bears in Portugal
Cave bears (Ursus spelaeus) were once widespread across Europe, but despite decades of digging, no hint of this species has ever been found in Portugal. By contrast, brown bears were abundant, and the study suggests this was no accident.
"They (cave bears) needed much larger caves than brown bears to hibernate, and the same maternal lineages came back to the same caves to hibernate for thousands and thousands of years," Estraviz-López said. He suspects cave bears simply never spread to Portugal.
Without a single cave bear in sight, brown bears may have stepped up to fill their role.
The bears from Furninha Cave, roughly 80,000 years old, were particularly striking. Many weighed more than 300 kg (about 660 pounds), but it was their build rather than their bulk that caught the researchers' attention. Holding the giant bones in his hands, Estraviz-López couldn't help but feel they were eerily similar to those of their extinct cousins, the cave bears. "Cave bears are a whole different league in terms of robustness," he said.
But the brown bears did not remain giants forever. By the early Holocene, roughly 12,000–8,000 years ago, males in northwestern Spain weighed about 260 kg (573 pounds) and females about 140 kg (310 pounds).
Brown bears kept getting smaller. Today, Iberian brown bears weigh roughly 144 kg (317 pounds) for males and 102 kg (225 pounds) for females. That's more than a 40% size drop for males and more than a 25% drop for females.
Thousands of years of shrinking
The size collapse cannot be explained solely by climate. Estraviz-López suggested human hunting may be to blame, and timing would have been key to success.
"Not a single guy with a spear would go after a fully awake bear of about 400 kg (880 pounds)," Estraviz-López said. "But while it is hibernating, for a group of experienced hunters setting careful plans, the task becomes easier."
The process would have been slow. At first, humans likely moved into the same caves as bears, then farmers destroyed their forests and finally sealed their fate when firearms made it easy to hunt them. "This prolonged pressure may have disproportionately removed the largest and boldest animals, favoring smaller bears that were less likely to come into conflict with humans," biologist Ana García-Vázquez, a co-author at the University of Bucharest, said.
The researchers call their timeline a working hypothesis, likening it to modern elephants being born tuskless due to hunting and poaching pressures.
García-Vázquez also cautions that the ancient giants and today's Iberian bears may not even be the same population. Diet may play a part, too, she said. "More carnivorous or fish-eating bears tend to grow larger." Ancient DNA and chemical analysis of the bones could settle the debate.
Either way, what was lost is more than just bulk. Bears are an important part of the ecosystem; Estraviz-López said they steal wolf kills, curb deer and boar numbers, and scatter seeds at an almost industrial scale.
"A single bear dropping can contain more than 70,000 seeds," Estraviz-López said, "and more than 91 rodents and birds can feed from those."
Understanding how Iberia's giants became today's survivors, he said, is the best guide we have to protecting the ones still out there.
Written for you by our author Sandee Oster, edited by Lisa Lock, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.
Publication details
Darío Estraviz-López et al, Pleistocene brown bears from Portugal: Morphometric trends, paleoenvironmental drivers and paleobiological inferences, Palaeogeography, Palaeoclimatology, Palaeoecology (2026). DOI: 10.1016/j.palaeo.2026.113964
Who's behind this story?
Archaeology PhD candidate at Witwatersrand. Science writer for Science X and archaeology blogger. Field research in South Africa. Full profile →
BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021. Full profile →
Bachelor's in mathematical biology, Master's in creative writing. Well-traveled with unique perspectives on science and language. Full profile →
© 2026 Science X Network
Citation: Portugal's ancient giant bears shrank over thousands of years and humans may be to blame (2026, July 23) retrieved 23 July 2026 from https://phys.org/news/2026-07-portugal-ancient-giant-shrank-thousands.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.