For decades, paleoanthropologists have largely agreed that somewhere along the evolutionary course from apelike ancestors to modern humans, our bodies got dramatically larger. However, one lingering mystery has been when this intense growth began.

Did our ancestors gradually grow bigger over millions of years? Did the shift coincide with the emergence of the genus Homo? Or did it occur later, after some of the earliest human species had already appeared?

A new study published in the Proceedings of the National Academy of Sciences (PNAS) argues that the answer is more complex than any single theory has suggested.

Rather than supporting a single long-standing hypothesis, researchers used a sophisticated statistical method to show that human body size likely followed two evolutionary courses simultaneously: a slow, steady increase spanning millions of years, punctuated by a much larger leap in later members of the genus Homo.

The findings help reconcile decades of conflicting research while offering one of the clearest pictures yet of how, and perhaps why, our ancestors evolved into larger-bodied humans.

“Despite its central role in hominin evolution, there is little consensus on how body size increased through time,” researchers write. “We provide strong evidence for a marked size increase in later-occurring Homo, alongside a moderate general increase over time among all hominins.”

Body size is one of the defining characteristics of an organism. In humans and our extinct relatives, it has been linked to everything from brain expansion and walking efficiency to metabolism, hunting behavior, and the ability to travel across increasingly large landscapes. Understanding when body size changed, therefore, helps researchers reconstruct not only what our ancestors looked like, but how they lived.

Yet despite decades of fossil findings, scientists have struggled to agree on the evolutionary pattern behind those changes.

Some previous studies suggested that hominins simply became larger over time. Some contended that body size remained relatively stable until the emergence of Homo. Still others have proposed that the real transformation arose only after early species such as Homo habilis, often regarded as one of the first members of our genus.

According to researchers, one reason for the disagreement is that earlier analyses typically examined these competing ideas independently. They also often failed to account for uncertainties inherent in the fossil record, including disagreements over species classification, differences in body mass estimation methods, and uncertainties in evolutionary relationships among fossil species.

To address those limitations, researchers compiled one of the largest hominin body-size datasets assembled to date, incorporating body mass assessments from 386 fossil specimens representing 21 different taxa.

They then analyzed the data using Bayesian phylogenetic generalized linear mixed models—a statistical approach that accounts for evolutionary relationships while encompassing multiple layers of uncertainty.

The team repeated its analyses across 1,000 different phylogenetic trees and 1,000 separate datasets, allowing them to test whether the overall pattern remained consistent despite uncertainties.

The results pointed to two simultaneous trends.

The first was a modest but persistent increase in body size across the hominin family as a whole. On average, body mass increased by roughly 2 pounds (0.9 kilograms) every million years, suggesting that larger bodies gradually became more common throughout human evolution.

However, the second trend proved far more dramatic.

Instead of all members of Homo becoming substantially larger, the researchers found the strongest evidence for a distinct jump in body size among later members of the genus, particularly species that appeared after Homo habilis. That pattern regularly emerged regardless of how the fossil data were analyzed.

In other words, early members of Homo may not have represented the major biological turning point scientists once assumed.

This finding disputes a common assumption that simply belonging to the genus Homo meant possessing a significantly larger body. Instead, the study suggests that some hallmark features traditionally associated with humans, including larger body size, may have evolved after the genus’s origin.

That interpretation also corresponds to broader changes that occurred later in human evolution.

Researchers note that this period coincides with evidence for more efficient upright walking, greater reliance on meat consumption, and expanding home ranges. Larger bodies may have been both a consequence of and a contributor to those behavioral and ecological shifts.

The study likewise reinforces another growing theme that evolution rarely follows a straight line.

Species such as Homo floresiensis, often nicknamed the “Hobbit” because of its diminutive stature, and Homo Naledi frequently appeared as outliers with unusually small body sizes despite belonging to relatively recent branches of the human family tree. Their existence demonstrates that body size did not simply increase in a uniform march toward modern humans.

Instead, evolution repeatedly experimented with different solutions depending on local environments and ecological constraints.

The researchers also argue that part of the longstanding disagreement over body-size evolution stems from the fossil record itself. Different studies have estimated fossil body masses using different skeletal elements, comparison populations, and statistical techniques, sometimes producing substantially different results for the same individual.

By expressly incorporating those uncertainties into their analysis, rather than treating them as fixed values, the new framework seeks to capture the range of plausible evolutionary scenarios rather than relying on a single interpretation.

Even so, researchers caution that important questions remain unresolved.

Improved fossil discoveries, more accurate body-mass estimation methods, and a better understanding of species relationships could all further refine the picture. The study also does not explicitly account for sexual size differences between males and females, which may have been greater in some early hominin species than in modern humans.

Nevertheless, the wider conclusion is intriguing.

Rather than choosing between competing theories, the evidence suggests both contain elements of the truth.

Body size did increase gradually across the hominin lineage. But the most considerable leap appears to have occurred later, after the earliest representatives of Homo had already evolved.

That conclusion may help settle one of paleoanthropology’s longest-running debates while showing how advances in statistical methods are transforming scientists’ ability to extract new insights from fossils that have often been studied for decades.

“Overall, these findings bring clarity to a fundamental question in human evolution and show how the application of rigorous phylogenetic comparative tools can unlock patterns previously hidden in the fossil record while accounting for multiple sources of uncertainty,” researchers write. “By reconciling conflicting findings within a single framework, our results clarify key evolutionary transitions and highlight the complex nature of body size change in human evolution.”

Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan.  Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com 

Until about 60,000 years ago, diminutive hominin cousins, Homo floresiensis (affectionately nicknamed Hobbits for obvious reasons), shared the island of Flores with Komodo dragons, pygmy elephants, and giant rats.

Based on the presence of hominin and pygmy elephant bones in the same layers of cave sediment, it originally looked like the Hobbits had hunted and butchered dwarf elephants—an impressive feat for such a tiny hominin. But according to University of Tübingen anthropologist Elizabeth Veatch and her colleagues, it was the Komodo dragons that were the hunters, while the Hobbits only showed up to scavenge what was left.

If Veatch and her colleagues are right, their findings may challenge some of the assumptions we’ve made about Homo floresiensis—and about which hominin species was the first to venture into the wider world beyond Africa.

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Homo floresiensis, a diminutive ancient hominin often compared to the hobbits of J.R.R. Tolkien’s Lord of the Rings mythos, engaged in a sort of “second breakfast” according to new research.

Instead of eating twice in short succession like their fictional counterparts, a new paper published in Nature Microbiology suggests that these hobbits were second to the table, eating the scavenged remains of Komodo dragon kills. This new work challenges earlier suggestions that H. floresiensis was a sophisticated species capable of using fire and hunting large game.

Interpreting The Hobbits of Flores

H. floresiensis remains have been discovered co-located with proboscideans, the taxonomic group that includes elephants, stegodons, and similar trunked creatures. One such discovery occurred on the island of Flores, off the coast of Indonesia, at the Liang Bua site.

Among the H. floresiensis and Stegodon remains at the site, small stone tools littered the area, leading researchers to conclude that the hobbits were ancient hunters.

The isolated conditions of the small island produced one of the most dwarfed Stegodon breeds, typically standing just under four feet tall and weighing between 770 and 800 pounds. In comparison, the hobbits were only a bit over three feet tall and weighed around 66 pounds, with the two species together forming almost a miniature scale model of the big-game hunting that later hominins would engage in elsewhere in the world.

The Secret of Fire

Archaeologists identified Stegodon remains bearing char marks, which they interpreted as evidence that the small hominins had mastered fire and were cooking their food. This was an unexpected find, as H. floresiensis was a relatively small-brained species, while evidence of fire use has typically been identified only in larger-brained species such as modern humans and Neanderthals.

The suggestion that the tiny, small-brained creatures killed and cooked Stegodon and other elephant ancestors led scientists to believe the species was relatively advanced. Potentially supporting this contention were skull measurements, indicating that despite the relatively small brain size, there was an expansion of the brain’s frontal polar region, associated with high-level cognitive processing. Taken together, this evidence led researchers to suspect that the hobbits were far more sophisticated than they had previously been given credit for.

Reconsidering Hobbits

However, when Smithsonian researchers reexamined the Stegodon bones found on Flores, they came to a different conclusion. Only one other creature on the island was a large enough predator to take down a Stegodon: the Komodo dragon. The Smithsonian team set out to investigate who was really behind the Stegodon kills: tiny hobbits, or giant lizards.

First, they performed an experiment at Zoo Atlanta, feeding Komodo dragons and then measuring the tooth marks on the leftover bones. Based on these baseline measurements, the researchers discovered Komodo dragon tooth marks on the meatiest, and therefore, most desirable parts of the carcass for predators to consume. It was only on the less desirable portions of the Stegodon remains that the team found cut marks likely caused by the hobbits. 

This indicates that Komodo dragons were most likely the original predators who killed the Stegodon, quickly taking the prime portions, with H. floresiensis coming later, like a hyena, to scavenge the remains. 

Additionally, their reinvestigation of H. floresiensis’s use of fire also called into question prior assertions. Only one of 3155 Stegodon bone fragments showed any evidence of contact with fire. That one fragment was unearthed high in the strata and may have poked through the surface of the site when it was used as a hearth by later H. sapiens, explaining the one odd incidence of fire damage.

In their final conclusion, the authors write, “The evidence to date thus suggests that H. floresiensis did not engage in a behavioral repertoire as diverse or as flexible as in modern humans or Neanderthals, possibly due to an ancestry in which large game hunting and controlled use of fire did not evolve”

The paper, “Taphonomic analysis at Liang Bua Reveals the Behavioral and Technological Capabilities of Homo Floresiensis,” appeared in Science Advances on July 3, 2026.

Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.

For decades, paleoanthropologists assumed that hominins -- the lineage leading to modern humans -- gradually grew larger over millions of years.

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