21:27 - We are just as smart now as we were in the ice age

Prof. Barkai: "In light of previous studies, our team proposed an original hypothesis that links the two questions: We think that large animals went extinct due to overhunting by humans, and that the change in diet and the need to hunt progressively smaller animals may have propelled the changes in humankind. In this study we tested our hypotheses in light of data from excavations in the Southern Levant covering several human species over a period of 1.5 million years." Jacob Dembitzer adds: "We considered the Southern Levant (Israel, the Palestinian Authority, Southwest Syria, Jordan, and Lebanon) to be an 'archaeological laboratory' due to the density and continuity of prehistoric findings covering such a long period of time over a relatively small area -- a unique database unavailable anywhere else in the world. Excavations, which began 150 years ago, have produced evidence for the presence of humans, beginning with Homo erectus who arrived 1.5 million years ago, through the neandertals who lived here from an unknown time until they disappeared about 45,000 years ago, to modern humans (namely, ourselves) who came from Africa in several waves, starting around 180,000 years ago."

Findings indicate a continual decline in the size of game hunted by humans as their main food source -- from giant elephants 1-1.5 million years ago down to gazelles 10,000 years ago. According to the researchers, these findings paint an illuminating picture of the interaction between humans and the animals around them over the last 1.5 million years.

In this way, according to the researchers, early humans repeatedly overhunted large animals to extinction (or until they became so rare that they disappeared from the archaeological record) and then went on to the next in size -- improving their hunting technologies to meet the new challenge. The researchers also claim that about 10,000 years ago, when animals larger than deer became extinct, humans began to domesticate plants and animals to supply their needs, and this may be why the agricultural revolution began in the Levant at precisely that time.

Multiple large-bodied species went extinct during the Pleistocene. Changing climates and/or human hunting are the main hypotheses used to explain these extinctions. We studied the causes of Pleistocene extinctions in the Southern Levant, and their subsequent effect on local hominin food spectra, by examining faunal remains in archaeological sites across the last 1.5 million years. We examined whether climate and climate changes, and/or human cultures, are associated with these declines. We recorded animal abundances published in the literature from 133 stratigraphic layers, across 58 Pleistocene and Early Holocene archaeological sites, in the Southern Levant. We used linear regressions and mixed models to assess the weighted mean mass of faunal assemblages through time and whether it was associated with temperature, paleorainfall, or paleoenvironment (C3 vs. C4 vegetation). We found that weighted mean body mass declined log-linearly through time. Mean hunted animal masses 10,500 years ago, were only 1.7% of those 1.5 million years ago. Neither body size at any period, nor size change from one layer to the next, were related to global temperature or to temperature changes. Throughout the Pleistocene, new human lineages hunted significantly smaller prey than the preceding ones. This suggests that humans extirpated megafauna throughout the Pleistocene, and when the largest species were depleted the next-largest were targeted. Technological advancements likely enabled subsequent human lineages to effectively hunt smaller prey replacing larger species that were hunted to extinction or until they became exceedingly rare.

The Southern Levant, situated between modern day southern Syria via Israel to Sinai, has a spatiotemporally dense and continuous Paleolithic archaeological record offering a unique opportunity to detect faunal changes, including those predating the appearance of Homo sapiens (Bar-Yosef, 1980; Stutz, 2014). It is thus a suitable model to test long-term changes in the body mass of mammalian assemblages, in view of paleoclimates and changing human lineages, to decipher whether climate and/or humans are responsible for animal body size declines. The excellent archaeological record can further illuminate whether size declines are observed since hominins first colonized the region, or whether they start with the emergence of Homo sapiens (Louys et al., 2021), or are concentrated in the last glacial and its aftermath. We tested whether the size, and size changes, in hominin prey through the Pleistocene and early Holocene were related to time, the prevailing human lineages and cultures, paleoenvironment, and temperatures.