Even a million and a half years ago, our ancestors understood that sometimes you need a simple hammerstone and other times a finely-made hand axe woul
Even a million and a half years ago, our ancestors understood that sometimes you need a simple hammerstone and other times a finely-made hand axe would better suit the task in front of you. New findings suggest that the Homo erectus toolkit was more diverse than previously believed. This challenges the simple single species/single technology thinking that has often been applied to early hominins.
An international team of researchers led by scientists from Spain and USA have found two H. erectus crania and a selection of tools that were used by our ancient ancestors in the Gona area in Afar, Ethiopia. These discoveries are important for two main reasons: first, they suggest that sexual dimorphism (color, size, shape, and/or structural differences between sexes in the same species) was present in H. erectus and second, the stone tools challenge the single species/single technology idea regarding hominin toolmaking use and abilities.
The DAN5 cranium, top/frontview. ( Dr. Michael J. Rogers, Southern Connecticut State University )
Evidence for Homo erectus sexual dimorphism
The Southern Connecticut State University news release explains that the researchers discovered two H. erectus crania, one nearly complete example dating to between 1.6- 1.5 million years ago, and one partial cranium from about 1.26 million years ago.
The older of the crania is the more complete example and was found in an area they call Dana Aoule North (DAN5). It is smaller and more gracile than the 1.26 million old robust example which was unearthed at Busidima North (BSN12), just 5.7 km (3.54 miles) away. The researchers say the smaller cranium has “the smallest endocranial volume documented for H. erectus in Africa, about 590 cubic centimeters.”
(A) DAN5/P1 neurocranium—four views: lateral, frontal, superior, and posterior. ( B) BSN12/P1 frontal—three views: superior (original fossil and cast), lateral, and frontal. ( C) BSN12/P1 vault—conjoined parietal and frontal viewed along midline anterior—is to the right. Scale bars, 40 mm (DAN5/P1) and 20 mm (BSN12/P1). ( Scott W. Simpson, Case Western Reserve University )
The scientists explain in their paper presented in the journal Science Advances that they believe that the small cranium was likely a female H. erectus and provides evidence that sexual dimorphism existed in the species; however they also admit that the difference between the crania may be due to more primitive anatomy still presenting itself in the older fossil.
One of the study’s authors, Michael Rogers from Southern Connecticut State University, explained to Newsweek why we want to know whether sexual dimorphism was present in H. erectus :
“For decades, and perhaps as recently as a decade ago or so, paleoanthropologists had thought of Homo erectus as exhibiting less sexual dimorphism than earlier hominins, based on the skeletal samples that had been measured. In just the last 10 to 15 years, though, with the discovery of a few smaller H. erectus crania—including the DAN5 cranium record-breaker—this view will certainly get a second look. If H. erectus is confirmed to be significantly sexually dimorphic throughout its long tenure, then the decrease in dimorphism among modern humans would be a more recent phenomenon, with interesting social implications.”
The Homo erectus toolkit was more complex than they’re given credit for
As Science News points out, “Hominid fossils and stone tools are rarely found together,” which makes these discoveries in Ethiopia even more exciting. Let’s move on to the fascinating world of stone tools as it presents itself in Gona, which, according to the university press release, provides “one of the earliest examples of H. erectus associated with both Oldowan and Acheulian stone assemblages.”
Two opposing views of Acheulian and Oldowan stone tools from the ( A) BSN12 and ( B) DAN5 sites. The Mode 1 cores are shown on the bottom row for each site. ( Michael J. Rogers, Southern Connecticut State University )
Specifically, it was found at the sites that while some of the Homo erectus tools have a single sharpened edge others were double-edged. Instead of only finding the expected large hand axes or picks, signature tools of H. erectus , the research team found both well-made hand axes and plenty of less-complex Oldowan tools and cores.
The story used to go: About 2 million years ago Homo habilis invented the first stone tools, which we call ‘Oldowan’ and these were very simple, then 1.8 to 1.7 million years ago Homo erectus changed toolmaking by creating large cutting tools such as hand axes – we call their tool technology ‘ Acheulian.’ This second toolmaking method allegedly took over from the simpler, earlier version.
But now the authors of the Science Advances paper say their work demonstrates that Oldowan stone tool technology continued to be used even after Acheulian technology was invented. This shows that the toolmakers were flexible in their choices and, according to the news release, H. erectus had a “cultural complexity” that has not been “fully understood or appreciated in paleoanthropology.”
“The simple view that a single hominin species is responsible for a single stone tool technology is not supported,” Rogers emphasized in the university press release. “The human evolutionary story is more complicated.”
The work that had to be done and the quality of rock options in the area likely played a role in which stone tool technology the individual chose.
Revealing the Homeland of the Prehistoric Toolmakers
Gona is in itself an interesting site to explore. It’s located in the Afar Triangle of Ethiopia, placing it by the more famous Middle Awash and Hadar sites, the homes of the famous skeletons “Ardi” and “Lucy,” respectively.
Isotope analysis on the older cranium found at Gona suggests that the individual had a heavily plant-based diet, but they also ate some animals that ate food from trees or shrubs. Environmental reconstruction of the Gona sites shows that rivers once flowed close to the prehistoric toolmakers’ habitats and there was woodland nearby as well.
Stone cobbles from the riverbed were taken by the H. erectus population to make tools and evidence of stone tool cut marks on an elephant toe bone and a percussion notch on an antelope leg bone indicates that they butchered both large and smaller animals, though the researchers are uncertain if the animals were hunted or scavenged by the toolmakers.
Reconstruction of Homo erectus based on bones found by Eugène Dubois, as displayed in the Naturalis Museum in Leiden, the Netherlands. Reconstruction made by Kennis & Kennis in 2019. (Hay Kranen/ CC BY 4.0 )
The multidisciplinary team used a variety of methods to discover more about the H. erectus toolmakers and their homeland. The university news release says that the scientists employed: “standard field mapping and stratigraphy, as well as analyses of the magnetic properties of the sediments, the chemistry of volcanic ashes, and the distribution of argon isotopes in volcanic ashes.”
University of Michigan geologist Naomi Levin, one of the members of the research team demonstrated the importance of having a variety of experts present for this type of research when she said,
“Constraining the age of these sites proved particularly challenging, requiring multiple experts using a range of techniques over several years of field work. This is a great example of scientific detective work and how science gets done, drawing on a community of scholars and their collective knowledge of the geology of eastern Africa.”
The fascinating findings of both physical and behavioral variation in the hominins as well as the detailed picture of what the Homo erectus toolmakers’ environment could have been like supports the notion of engaging a multidisciplinary team to explore our distant past whenever possible.
Top Image: This small, gracile, almost complete cranium was found near Homo erectus tools in Ethiopia. Source: Dr. Michael J. Rogers, Southern Connecticut State University