The study was led by doctoral student Vlad Litov, Dr. Miki Ben-Dor, and Prof. Ran Barkai of Tel Aviv University’s Alkow Department of Archaeology, Entin Faculty of Humanities. Prof. Barkai is a leading authority on ancient Paleolithic cultures. The findings were published in the academic journal Quaternary Science Reviews.

From Giant Animals to Smaller Prey

Vlad Litov: “During the Lower Paleolithic period (approximately 2 million to 200,000 years ago), humans routinely used heavy-duty tools such as handaxes, cleavers, and massive scrapers. These tools were particularly well suited for butchering and processing the very large animals that served as a primary food source for humans throughout this period. However, with the transition to the Middle Paleolithic period, around 200,000 years ago, heavy-duty tools almost completely disappeared and were replaced by smaller, lighter, and more sophisticated tools. Until now, this shift has been attributed to advances in human cognition. In our new study, we propose a different interpretation: the dramatic decline in the prevalence of megaherbivores was the key driver of this technological change.”

Prehistoric Stone Tool Types

The researchers analyzed dozens of archaeological sites in the Levant and compared the types of tools with the composition of the animal remains found at the sites. The findings show that in earlier periods, large animals dominated both in biomass and in species prevalence and diversity, while in later periods their presence sharply declined, alongside an increase in the hunting of small and medium-sized animals.

According to the researchers, heavy-duty tools were essential for high-intensity tasks such as butchering large animals and breaking bones in order to extract substantial quantities of meat and marrow. As these animals disappeared, the need for these types of tools diminished, and humans shifted to lighter, smaller tools better suited to processing smaller prey. In the absence of large game, early hunters were forced to target greater numbers of smaller mammals, such as fallow deer, which yielded less meat and fat. The smaller tools enabled more efficient processing of large quantities of smaller animals, while the heavy-duty tools, such as the handaxe, lost their functional relevance.

Environmental Change May Have Driven Human Evolution

The researchers note that the study offers a broader perspective on human evolution: technology is shaped not only by cognitive abilities, but also by environmental conditions and the animals that coexisted with humans. In fact, environmental changes may have driven cognitive and technological development — and not the other way around.

Prof. Barkai concludes: “The findings shed new light on the relationship between early humans and their environment, highlighting how profound ecological changes can shape human culture, technology, and ways of life over time. Our study suggests that the dramatic technological shifts of prehistory were not the result of a sudden leap in human cognitive abilities, but rather a direct response to major environmental change. As the megaherbivores — a key source of food — gradually diminished, humans were forced to adapt to a new reality of hunting and processing smaller prey. The transition to lighter, more precise tools reflects this adaptation. In this sense, the environment not only influenced early humans, but directly shaped their technology, and perhaps even their cultural and cognitive development.”

The study was led by Dr. Tzachi Knaan as part of his doctoral research in the laboratory of Prof. Yftach Gepner of the School of Public Health and the Sylvan Adams Sports Institute at Tel Aviv University. It was conducted in collaboration with Prof. Ed Melanson of the University of Colorado, Prof. Gal Dubnov-Raz, Prof. Carmit Levy, Prof. Chen Luxenburg, and additional students from the participating laboratories. The findings were published in the journal Communications Medicine.

The Body Burns Less Energy Elsewhere

Participants who were overweight were recruited for the study and completed a supervised aerobic walking program (4–5 times per week) over a 12-week period. Throughout the study, energy expenditure, activity levels, dietary intake, and even changes in body composition were precisely measured using advanced technologies. Despite burning hundreds of calories per week through physical activity and improving their overall fitness, participants did not lose weight. However, they did show improvements in body composition, with reductions in fat and increases in muscle mass.

So why didn’t their body weight change? According to the researchers, the body simply adapted to the new situation. Among other findings, they observed a decline in resting metabolic rate, indicating that the body offset the increased activity by burning fewer calories at rest. In addition, participants became more efficient in their movements, expending less energy while performing the same daily activities.

Another surprising finding concerns the body’s internal organs: the researchers found a decrease of about 5 percent in the volume of the liver and kidneys — major energy consumers — while the brain remained unchanged. The implication is that the body reduces its internal energy expenditure in order to compensate for the increased demands of physical activity.

However, contrary to common assumptions, the researchers found no significant increase in food intake. In other words, the observed compensation does not stem from eating more, but from physiological and metabolic adaptations that reduce total energy expenditure.

“The Human Body Is Extremely Sophisticated”

Dr. Tzachi Knaan explains: “The human body is extremely sophisticated — it knows how to adapt itself to maintain balance. Physical activity is very important for good health, but when it comes to weight loss, it is not always sufficient on its own. The implication for the public is clear: exercise is a vital component of a healthy lifestyle — it improves fitness, reduces fat, and improves health indicators — but to see significant weight loss, it must be combined with the appropriate nutrition.”

The researchers note that the new study sheds light on one of the major questions in health and fitness and may even change the way we think about weight loss. Instead of relying on exercise alone, the most effective approach is likely to involve a proper combination of physical activity, nutrition, and an understanding of the body’s mechanisms.

Prof. Yftach Gepner concludes: “This study offers a window into an evolutionarily rooted mechanism of energy compensation. In the past, when food was not available near the tribe, hunters and gatherers had to travel considerable distances, necessitating a reduction in energy expenditure in order to successfully return to the tribe with food. The central message is that physical activity alone is not designed to reduce weight. For years, science has shown that weight loss resulting from exercise is more limited than commonly expected, and in this study, for the first time, the mechanism of organ shrinkage that explains this phenomenon was observed. It is important to emphasize that physical activity has unique and substantial health benefits — but it is not intended, on its own, to lead to weight loss.”