In Dr. Kidder's ongoing series tracing the history of the human fossil record, the last few posts focused on homo erectus. Today's post marks the transition from homo erectusto archaic homo sapiens, which took place more than a half-million years ago.
Beginning around 1.6 million years ago, the first large-brained hominin appeared on the landscape. This was Homo ergaster. Homo ergaster had a modern skeleton and more advanced food-gathering methods than previous hominins. It was also the first hominin to make it out of Africa, its earliest remains having being found in Dmanisi, in the Republic of Georgia and, a bit later, in several places in southern Europe.
Our best understanding is that this form gave rise to Homo erectus around a million years ago, and that by 700,000 years ago, Homo erectus was firmly established as the dominant (if not the only) hominin on the landscape. From the river valleys in Indonesia, to the open savannas in Africa, to the caves in China, India and Europe, this hominin had mastered fire, standardized stone tool technology and incorporated hunting into its daily life. Through the approximately million-year heyday of Homo erectus, the Acheulean tool technology—focused on the hand axe—remained unchanged. But, yet again, change was on the horizon: beginning around 600 to 700 thousand years ago, new hominin forms appear in the archaeological record, all having certain common characteristics that represent advancements over those found in Homo erectus. These were the first, still-archaic Homo sapiens.
Cranial capacity in these new hominins increased from the Homo erectus average of 900 CC3 to an average of 1100 CC3, with the heads becoming larger and more vaulted. The maximum cranial width was now midway up the sides of the vault, rather than near the ears as was the case with Homo erectus. In fact, some of the archaic Homo sapiens crania are among the largest skulls found. Faces are also larger; as are front teeth, and the faces do not project out as much as with prior types, having a more orthognathic (flatter) appearance. The extensive brow ridges—which formed a continuous bar in Homo erectus—are now divided in the middle, above the nose. As with every other stage of human evolution, we must start with the primary fossil remains before discussing their taxonomic status; and that means beginning with the record preserved in Africa.
As Bräuer notes (Bräuer, 2012), hominins that are distinctly different from their Homo erectus precursors appear on the landscape in Africa between 600 and 700 thousand years ago. While only a partial cranium, the find of Bodo, in east Africa, possesses the largest face of any hominin yet recorded. This individual has alternatively been described as “developed Homo erectus” and “Early Archaic Homo sapiens,” and has been dated to around 600,000 years ago (Figure 1). Despite its size, this cranium represents a shift toward a form in the direction of modern humans; a less scooped face, a brow ridge that is now separate rather than one continuous bar, and a cranial capacity of slightly over 1300 CC3.
Perhaps one of the most famous (and complete) skulls that has ever been discovered came from the Broken Hill mine in what was then known as Rhodesia. Known for decades as Broken Hill 1 (Figure 2), it is now more commonly called Kabwe. This is a visually stunning skull, with a very large face and enormous brow ridges. The cranial capacity is around 1100 CC3 and the head is sloping and long. This cranium is thought to be around 300,000 years old. Very similar to Kabwe, at least in cranial morphology, is the find from Saldanha (Figure 3). This has a low, sloping forehead, large supraorbital tori and a very sharply-angled rear of the vault. It has been estimated to be around 400 thousand years old.
From the site of Laetoli, which yielded the phenomenal footprints of one of our earliest ancestors,Australopithecus afarensis, comes a cranium described by Magori and Day (1983) as “…Homo sapiens but of an archaic variety” (Figure 4) This skull shows many similarities to Saldanha and Kabwe, being long and low with prominent brow ridges. The date for this hominin places it late in the sequence (120,000 plus or minus 30,000), but this date is based on an assumed correlation with beds at Olduvai and may not be correct. While it is clearly archaic, an associated face shows considerable reduction in size, toward the modern condition, suggesting that, at least for some populations, selection for smaller facial features was occurring and did not go in concert with comparable changes in the vault.
This pattern is also evident in a find from North Africa, from the Atlas Mountains of Morocco. Here was unearthed the Jebel Irhoud (or Ighoud) 1 cranium (Figure 5). Dated to approximately the same time as the given date for LH18, this cranium still has quite prominent brow ridges and is long and low but the face is considerably reduced and pulled in under the forehead.
It is clear that African post-Homo erectus morphology was in a state of flux for some time—possibly several hundred thousand years, judging from the wide morphological variability that we find. It is this variability that had led many researchers to use the “archaic Homo sapiens” designation (see below), since the task of drawing relationships based on derived and primitive traits has revealed few clues in the overall evolution of these hominins. We know that they are getting more modern over time because we see this in individual skulls but the overall pattern is difficult to quantify.
It must be remembered that, for most of this time period, the variability that we speak of is seen in the cranium. This is for two reasons: first, remains other than the cranium are scant and often fragmentary; second, what we do have of such post cranial remains are not appreciably different from anatomically modern humans. At approximately one million years ago, our ancestors attained what is basically a modern skeleton. These hominins are obligate bipeds, some are between five and six feet tall, and their bone structure is modern.
In recent decades, there has been a bit of a renaissance of work in Europe and many critical discoveries have been made that shed light on the evolution of these forms and the origins of perhaps the most well-known variant of archaic Homo sapiens, the Neandertals. One of the most impressive fossil hominin and archaeological sites in Europe comes from the town of Atapuerca, in northern Spain. This site contains material stretching from just over a million years ago down to 300 thousand years. Discovered in 1981, the Atapuerca cave system contains three major sites, the Gran Dolina, the Sima del Elefante and the Sima de Los Huesos. Systematic excavation turned up stone tools in 1991 (Rodríguez et al., 2011). Of particular note, however, was the huge quantity of human fossil remains that stretch for almost the entire vertical distance at the site. Morphologically, these hominins are quite varied. The Gran Dolina cave, which is the earliest of the group, yielded hominin remains that date to around 800,000 years ago. These remains (Figure 6), which consist of cranial, facial and dental materials, suggest a mix of primitive and modern traits. The dentition is large, a carryover from Homo erectus, while the facial skeletons show some modern characteristics in that parts of the face are everted, as in modern humans. Other characteristics are derived in the direction of Neandertals, however. The nasal bones stick out, a trait not found in Homo erectus. This combination of traits has led the researchers to hypothesize that these remains reflect the last common ancestor to modern humans and Neandertals (Arsuaga et al., 1999). It is not clear at present, though, that we can say for sure what the morphology of these hominins represents.
Further up in time come the remains from the site of Sima de Los Huesos. These remains are likely between 300 and 400 thousand years old. According to the describers of the fossil skeletal material found there, these remains “document an early stage of Neanderthal evolution.”(Arsuaga, Martinez, Gracia, Carretero, & Carbonell, 1993). Among the over 4000 remains found at the site are two complete and one partially complete skull (Figure 7). The skulls are notable for their massive brow ridges and faces. Further, the facial skeletons are quite unlike that found in the Gran Dolina. These skulls are characterized by what is known as midfacial prognathism, a trait exemplified by the later Neandertals. It is as if someone has grabbed the nose and pulled the face out from the middle.
Another find of great antiquity in Europe comes from the site of Ceprano, (Figure 8) midway between Rome and Naples, in Italy. It is a partial cranium with associated crude bifaces that are little more advanced than the Developed Oldowan tools crafted by the hominins that preceded it (Ascenzi, Biddittu, Cassoli, Segre, & Segre-Naldini, 1996). This hominin has been dated to around 800,000, placing it half a million years after the archaeological material at Pirro Nord. (See the previous post in this series, Out of Africa (The First Time) for more on Pirro Nord.)
One of the most important finds from Europe comes from the site of Petralona near the town of Thessaloniki, in Greece. Discovered in 1960, this is one of the most complete fossil human crania in existence and has an estimated cranial capacity of over 1200 cc. This skull is very large and long, with a sloping forehead, large eye orbits and rugose (ridged and wrinkly) features. In many ways, it is a dead ringer for SH5 from Atapuerca, having a very pneumatized (puffy) face that is pulled out from the midline of the skull and very strong brow ridges (Figure 9). These similarities suggest a generalized pan-European form between 300 and 500 thousand years ago. Like the Atapuerca skull, this one has what can be called “incipient” Neandertal morphology and, given that Neandertal remains have been found in the Greek isles and in nearby Italy, it is reasonable to suggest that there was widespread positive selection for these traits. Any gene flow between these populations would have further reinforced these changes.
From Germany come two more important finds: the Mauer mandible and the Steinheim calvaria. The Steinheim find is considerably smaller than the Petralona individual and is very gracile in appearance. The skull is quite fragmentary, having been crushed postmortem (Figure 10). Like many of its contemporaries, it has a long, low skull. It does, however, show general rounding of the back of the cranium and a more flattening of the face.
The Mauer mandible is large, suggesting a massive individual. It has no clear Neandertal traits, instead resembling a generalized archaic Homo sapiens form. Discovered in 1908 during a mining operation, this find has been dated at around 500,000 years (Figure 11). Like the Steinheim skull, though, it has characteristics advanced over Homo erectus, with teeth intermediate in size between that form and the Neandertals that followed. It is this fossil that is the hypodigm of Homo heidelbergensis—that is, the sample from which the characters of that population is to be inferred.
From France comes the important skull from the site of Arago (Figure 12). The cranial remains consists only of the face and frontal bone (the rest has been reconstructed on the figure to the left) but the face is relatively undistorted, revealing a morphology similar to that of SH5 from Atapuerca and Petralona, with heavy brow ridges and large maxillary sinuses. A mandible and partial pelvis were discovered along with the cranial remains. Through biostratigraphy and uranium series dating, the find is thought to be between 300 and 400 thousand years old, making it contemporary with those similar remains.
Archaic Homo sapiens: A Taxonomic Mess
One of the greatest challenges facing students of human evolution comes at the tail end of the Homo erectus span. After Homo erectus, there is little consensus about what taxonomic name to give the hominins that have been found. As a result, they are assigned the kitchen-sink label of “archaic Homo sapiens.”
Tattersall (2007) notes that the Kabwe skull bears more than a passing resemblance to one of the most prominent finds in Europe, the Petralona skull from Greece. In turn, as I mentioned above, the Petralona skull is very similar to one of the most complete skulls from Atapuerca, SH 5, and at least somewhat similar to the Arago skull.
Further, it is noted that the Bodo cranium from Africa shares striking similarities to the material from Gran Dolina (such as it is). This suggests that, as was the case with Homo erectus, there is widespread genetic homogeneity in these populations. Given the time depth involved, it is likely that there was considerable and persistent gene flow between them. Tattersall (2007), argues that, since the first example of this hominin form is represented by the Mauer mandible, the taxonomic designation Homo heidelbergensis should be used to designate these forms. This would stretch the limits of this taxon, however, since it would include the later forms from Africa as well. If there was considerable migration and hybridization between these populations, it could be argued that a single taxon makes sense. However, at present, there is no definitive material evidence for such migration, or widespread agreement on calling all these hominins anything other than “archaic Homo sapiens.”
Next, East Asian Archaic Homo sapiens.
Arsuaga, J.-L., Martinez, I., Gracia, A., Carretero, J.-M., & Carbonell, E. (1993). Three new human skulls from the Sima de los Huesos Middle Pleistocene site in Sierra de Atapuerca, Spain. [10.1038/362534a0]. Nature, 362(6420), 534-537.
Arsuaga, J.-L., Martínez, I., Lorenzo, C., Gracia, A., Muñoz, A., Alonso, O., et al. (1999). The human cranial remains from Gran Dolina Lower Pleistocene site (Sierra de Atapuerca, Spain). Journal of human evolution, 37(3‚Äì4), 431-457.
Ascenzi, A., Biddittu, I., Cassoli, P. F., Segre, A. G., & Segre-Naldini, E. (1996). A calvarium of lateHomo erectusfrom Ceprano, Italy. Journal of human evolution, 31(5), 409-423.
Bräuer, G. (2012). Middle Pleistocene Diversity in Africa and the Origin of Modern Humans. In J.-J. Hublin & S. P. McPherron (Eds.), Modern Origins (pp. 221-240): Springer Netherlands. Magori, C. C., & Day, M. H. (1983). Laetoli Hominid 18: an early Homo sapiens skull. Journal of human evolution, 12(8), 747-753.
Rodríguez, J., Burjachs, F., Cuenca-Bescós, G., García, N., Van der Made, J., Pérez González, A., et al. (2011). One million years of cultural evolution in a stable environment at Atapuerca (Burgos, Spain). Quaternary Science Reviews, 30(11‚Äì12), 1396-1412.
Tattersall, I. (2007). Homo ergaster and Its Contemporaries. In W. Henke & I. Tattersall (Eds.), Handbook of Paleoanthropology (pp. 1633-1653): Springer Berlin Heidelberg.