Homo erectus dmanisi

Skull of Homo erectus throws story of human evolution into disarrayA haul of fossils found in Georgia suggests that half a dozen species of early human ancestor were actually all Homo erectus

Ian Sample, science correspondent

The Guardian, Thursday 17 October 2013 19.00 BST http://www.theguardian.com/science/2013/oct/17/skull-homo-erectus-human-evolutionLink to video: Fossil skull challenges understanding of human evolution

The spectacular fossilised skull of an ancient human ancestor that died nearly two million years ago has forced scientists to rethink the story of early human evolution.

Anthropologists unearthed the skull at a site in Dmanisi, a small town in southern Georgia, where other remains of human ancestors, simple stone tools and long-extinct animals have been dated to 1.8m years old.

Experts believe the skull is one of the most important fossil finds to date, but it has proved as controversial as it is stunning. Analysis of the skull and other remains at Dmanisi suggests that scientists have been too ready to name separate species of human ancestors in Africa. Many of those species may now have to be wiped from the textbooks.

The latest fossil is the only intact skull ever found of a human ancestor that lived in the early Pleistocene, when our predecessors first walked out of Africa. The skull adds to a haul of bones recovered from Dmanisi that belong to five individuals, most likely an elderly male, two other adult males, a young female and a juvenile of unknown sex.

The five H erectus skulls found in Dmanisi, Georgia. Photograph: Ponce de Leon, Zollikofe/University of Zurich

The site was a busy watering hole that human ancestors shared with giant extinct cheetahs, sabre-toothed cats and other beasts. The remains of the individuals were found in collapsed dens where carnivores had apparently dragged the carcasses to eat. They are thought to have died within a few hundred years of one another.

"Nobody has ever seen such a well-preserved skull from this period," said Christoph Zollikofer, a professor at Zurich University's Anthropological Institute, who worked on the remains. "This is the first complete skull of an adult early Homo. They simply did not exist before," he said. Homo is the genus of great apes that emerged around 2.4m years ago and includes modern humans.

Other researchers said the fossil was an extraordinary discovery. "The significance is difficult to overstate. It is stunning in its completeness. This is going to be one of the real classics in paleoanthropology," said Tim White, an expert on human evolution at the University of California, Berkeley.

But while the skull itself is spectacular, it is the implications of the discovery that have caused scientists in the field to draw breath. Over decades excavating sites in Africa, researchers have named half a dozen different species of early human ancestor, but most, if not all, are now on shaky ground.

The most recently unearthed individual had a long face and big teeth, but the smallest braincase of all five H erectus skulls found at the site. Photograph: Georgian National Museum

The remains at Dmanisi are thought to be early forms of Homo erectus, the first of our relatives to have body proportions like a modern human. The species arose in Africa around 1.8m years ago and may have been the first to harness fire and cook food. The Dmanisi fossils show that H erectus migrated as far as Asia soon after arising in Africa.

The latest skull discovered in Dmanisi belonged to an adult male and was the largest of the haul. It had a long face and big, chunky teeth. But at just under 550 cubic centimetres, it also had the smallest braincase of all the individuals found at the site. The dimensions were so strange that one scientist at the site joked that they should leave it in the ground.

The odd dimensions of the fossil prompted the team to look at normal skull variation, both in modern humans and chimps, to see how they compared. They found that while the Dmanisi skulls looked different to one another, the variations were no greater than those seen among modern people and among chimps.

The scientists went on to compare the Dmanisi remains with those of supposedly different species of human ancestor that lived in Africa at the time. They concluded that the variation among them was no greater than that seen at Dmanisi. Rather than being separate species, the human ancestors found in Africa from the same period may simply be normal variants of H erectus.

"Everything that lived at the time of the Dmanisi was probably just Homo erectus," said Prof Zollikofer. "We are not saying that palaeoanthropologists did things wrong in Africa, but they didn't have the reference we have. Part of the community will like it, but for another part it will be shocking news."

Reconstruction of the early human ancestor Homo erectus from the latest skull found at Dmanisi in Georgia. Illustration: J H Matternes

David Lordkipanidze at the Georgian National Museum, who leads the Dmanisi excavations, said: "If you found the Dmanisi skulls at isolated sites in Africa, some people would give them different species names. But one population can have all this variation. We are using five or six names, but they could all be from one lineage."

If the scientists are right, it would trim the base of the human evolutionary tree and spell the end for names such as H rudolfensis, H gautengensis, H ergaster and possibly H habilis.

The fossil is described in the latest issue of Science.

"Some palaeontologists see minor differences in fossils and give them labels, and that has resulted in the family tree accumulating a lot of branches," said White. "The Dmanisi fossils give us a new yardstick, and when you apply that yardstick to the African fossils, a lot of that extra wood in the tree is dead wood. It's arm-waving."

"I think they will be proved right that some of those early African fossils can reasonably join a variable Homo erectus species," said Chris Stringer, head of human origins at the Natural History Museum in London. "But Africa is a huge continent with a deep record of the earliest stages of human evolution, and there certainly seems to have been species-level diversity there prior to two million years ago. So I still doubt that all of the 'early Homo' fossils can reasonably be lumped into an evolving Homo erectus lineage. We need similarly complete African fossils from two to 2.5m years ago to test that idea properly."

The analysis by Lordkipanidze also casts doubt on claims that a creature called Australopithecus sediba that lived in what is now South Africa around 1.9m years ago was a direct ancestor of modern humans. The species was discovered by Lee Berger at the University of Witwatersrand. He argued that it was premature to dismiss his finding and criticised the authors for failing to compare their fossils with the remains of A sediba.

"This is a fantastic and important discovery, but I don't think the evidence they have lives up to this broad claim they are making. They say this falsifies that Australopithecus sediba is the ancestor of Homo. The very simple response is, no it doesn't."

"What all this screams out for is more and better specimens. We need skeletons, more complete material, so we can look at them from head to toe," he added. "Any time a scientist says 'we've got this figured out' they are probably wrong. It's not the end of the story."

This article was amended on 18 October 2013. An earlier version incorrectly located Georgia in central Asia.

Newly-Discovered Fossilized Skull Could Prove Homo Erectus Sole Human Ancestor

25 33 0

Email Article Print article Send a Tip

by William Bigelow 20 Oct 2013 http://www.breitbart.com/Big-Peace/2013/10/19/New-Fossilized-Skull-Means-Home-Erectus-Sole-Human-AncestorA new discovery of an ancient skull from an ancestor of humans has scientists backtracking from their earlier claims that separate species in Africa were the progenitors of the human race.

The skull, found in the Georgian villiage of Dmanisi, is roughly two million years old and is the only intact human ancestors skull ever found that dates from the early Pleistocene Era. Dmanisi has yielded bones thought to be the remains of three males, one of them elderly, a young female, and a child whose sex is indeterminate.

Christoph Zollikofer, a professor at Zurich University's Anthropological Institute, said, "Nobody has ever seen such a well-preserved skull from this period. This is the first complete skull of an adult early Homo. They simply did not exist before. His awe was echoed by Tim White, from the University of California, Berkeley, who said, "The significance is difficult to overstate. It is stunning in its completeness. This is going to be one of the real classics in paleoanthropology." The Dmanisi bones are believed to be remnants of Homo erectus, the first ancestor who resembled modern humans and originated in Africa.

Zollikofer continued, "Everything that lived at the time of the Dmanisi was probably just Homo erectus. We are not saying that palaeoanthropologists did things wrong in Africa, but they didn't have the reference we have. Part of the community will like it, but for another part it will be shocking news."

The leader of the Dmanisi excavations, David Lordkipanidze, said, "If you found the Dmanisi skulls at isolated sites in Africa, some people would give them different species names. But one population can have all this variation. We are using five or six names, but they could all be from one lineage." Lordkipanidze theorized that the belief that Australopithecus sediba was a direct ancestor of humans was now probably wrong.

The consequences of the Dmanisi discovery could mean that species such as Homo rudolfensis, Homo gautengensis, Homo ergaster, and possibly Homo habilis would be dismissed.

White explained:

Some palaeontologists see minor differences in fossils and give them labels, and that has resulted in the family tree accumulating a lot of branches. The Dmanisi fossils give us a new yardstick, and when you apply that yardstick to the African fossils, a lot of that extra wood in the tree is dead wood. It's arm-waving.

But Chris Stringer, head of human origins at the Natural History Museum in London, took issue with the idea that Homo Erectus was solely responsible for the ancestry of humans, saying:

I think they will be proved right that some of those early African fossils can reasonably join a variable Homo erectus species. But Africa is a huge continent with a deep record of the earliest stages of human evolution, and there certainly seems to have been species-level diversity there prior to two million years ago. So I still doubt that all of the 'early Homo' fossils can reasonably be lumped into an evolving Homo erectus lineage. We need similarly complete African fossils from two to 2.5m years ago to test that idea properly.

Lee Berger, at the University of Witwatersrand, who discovered the species Australopithecus sediba, took issue with the conclusion drawn by the Dmanisis team. He said:

This is a fantastic and important discovery, but I don't think the evidence they have lives up to this broad claim they are making. They say this falsifies that Australopithecus sediba is the ancestor of Homo. The very simple response is, no it doesn't. What all this screams out for is more and better specimens. We need skeletons, more complete material, so we can look at them from head to toe. Any time a scientist says 'we've got this figured out' they are probably wrong. It's not the end of the story.

Homo Georgicus: Georgia skull may prove early humans were single species

Published time: October 18, 2013 14:34 Edited time: October 19, 2013 19:43 http://rt.com/news/skull-homo-georgia-species-373/Get short URL

David Lordkipanidze, director of the Georgian National Museum, holding a well-preserved skull from 1.8 million years ago found found in the remains of a medieval hilltop city in Dmanisi on October 18, 2013 (AFP Photo / Vano Shlamov)

A 1.8 million-year-old skull found in Georgia could turn current understanding of evolution on its head. A new study claims that early man did not come from Africa as seven species, but was actually a single homo erectus with variations in looks.

The case revolves around an early human skull found in a stunningly well-preserved state at an archaeological dig at the site of the medieval hill city of Dmanisi in Georgia, a study in the journal Science revealed on Thursday.

Stone tools were found next to the remains, indicating that the species hunted large carnivorous prey, including probably saber-toothed tigers.

A team of scientists spent over eight years studying the find, whose original date of excavation was 2005. Its jawbone was actually discovered back in 2000, but only recently have the parts been assembled to produce a complete skull.

New dating technology allowed scientists to establish that these early humans come from around 1.8 million years ago. Near to the bone fragments were the remains of huge prehistoric predators; the area is next to a river and was full of them, as they encountered humans in fights to the death.

The skull has a tiny brain about a third of the size of our modern Homo sapiens incarnation; it also has protruding brows, jutting jaws and other characteristics we have come to expect from lesser developed prehistoric humans. But the surprising revelation came when the skull was placed next to four other skulls discovered within a 100-kilometer radius. They vary so much in appearance that it brings into question whether the current understanding of species variation is correct.

Traditional theories accept a whole plethora of stand-alone species but the new find strongly hints that the five remains were all one, but with striking differences in bone structure that we have come to expect only from our own complex kind.

This handout photo received October 17, 2013 shows a complete, approximately 1.8-million-year-old hominid skull from Dmanisi, Georgia (AFP Photo / Georgian National Museum / Handout)

Director of the Georgian National Museum and lead researcher, David Lordkipanidze, has come out with the claim that the find is "the richest and most complete collection of indisputable early Homo remains from any one site." "Dmansi is a unique snapshot of time maybe a time capsule that preserves things from 1.8 million years ago," he told AFP.

Adding weight to the new hypothesis, co-author of the study, Christoph Zollikofer of the University of Zurich, judged that despite the striking dissimilarities we know that these individuals came from the same location and the same geological time, so they could, in principle, represent a single population of a single species.

The differences in the skulls eyebrow ridges, jaws and other features were all consistent with what paleontologists expect of variations within the same species.

"The five Dmanisi individuals are conspicuously different from each other, but not more different than any five modern human individuals, or five chimpanzee individuals, from a given population," Zollikofer continued.

This has led scientists to conclude that, while previously we thought that intra-species variation was an exception, it could very well be a rule instead.

For decades researchers would separate all types of humans originating in Africa into separate sub-groups with examples including the Homo habilis, the Homo rudolfensis, and so on. The new hypothesis suggests these could all just be Homo erectus, with the regular human variation in bone structure we witness in our own Homo sapiens peers. 3D modeling shows this clearly.

It also challenges the notion that we needed a larger cranial capacity or brain in order to be intelligent enough to use complex tools, hunt large prey and migrate to distant continents. It appears the humans found at the Georgian site actually migrated to Asia despite not being very bright.

Milford Wolpoff of the University of Michigan told AFP that the team was thrilled about the conclusion they came to. It backs up what we found as well. He was working with a colleague from Wellesley College during a study they published a year ago, which also targeted statistical variations in characteristics of skulls from Georgia and East Africa considered to be one of the cradles of human civilization.

The study suggested active inter-species breeding was commonplace back in those days.

"Everyone knows today you could find your mate from a different continent and it is normal for people to marry outside their local group, outside their religion, outside their culture[but] what this really helps show is that this has been the human pattern for most of our history, at least outside of Africa, Wolpoff explained.

However, challengers to the hypothesis believe otherwise. Their main qualm with the hypothesis is that the skull may simply have belonged to a new species of human not a variation of Homo erectus.

Bernard Wood of George Washington University believes the conclusions of the Dmanisi research team to be misguided.

"What they have is a creature that we have not seen evidence of before, Wood said in reference to the small head but human-looking body of the early hominid.

Wood feels that the small human has been deprived of what could rightfully be a separate Homo a Homo georgicus.

However, this matters little to the case at hand that a new form of human has been discovered and that its practices strongly suggest that its life patterns and differences in features very closely mimicked what we see today in our modern selves.

Homo erectus - A Bigger, Smarter, Faster Hominin Lineage

By:Adam P. Van Arsdale(Department of Anthropology, Wellesley College)2013Nature Education

Citation:Van Arsdale,A.P.(2013)Homo erectus - A Bigger, Smarter, Faster Hominin Lineage.Nature Education Knowledge4(1):2

http://www.nature.com/scitable/knowledge/library/homo-erectus-a-bigger-smarter-97879043About two million years ago, a new set of fossils began to appear in the human fossil record. Designated as Homo erectus, they show evidence of increases in both body size and brain size.

Homo erectus is arguably the earliest species in the human lineage to have so many human-like qualities. Earlier hominins had important similarities with living humans, like bipedality, and H. erectus still had a long evolutionary path to become like you and me, but the fossils assigned to H. erectus display a number of new and distinctly modern human traits.

Homo erectus is often referred to as the first cosmopolitan hominin lineage, meaning the first hominin species whose geographic range had expanded beyond a single continental region. While fossil remains from H. erectus are found in Africa, like those of earlier hominins, they have also been identified at fossil sites widely dispersed across Eurasia (Figure 1, Table 1).

Figure 1:Map of Homo erectus fossil localities.

2012 Nature Education All rights reserved.

Date (mya)LocalityKey Fossils

1.9 1.2Koobi Fora, KenyaWT 15000 (Nariokotome), ER-3733, ER-3883

1.9 0.7Olduvia Gorge, TanzaniaOH 9, OH 12

1.8 1.7Dmanisi, GeorgiaD3444, D2700, D2280, D2282

1.8 1.6Swartkrans, South AfricaSK 847

1.8 0.9Sangiran/Trinil, IndonesiaTrinil 2, Mojokerto, Sangiran 17, Sangiran 2

1.0 0.8Ceprano, ItalyCeprano 1

0.8 0.4Zhoukoudian, ChinaZKD E1, D1, L1, L2, H3

0.8 0.6Bodo, EthiopiaBodo

0.6 0.3Atapuerca, SpainSima de los huesos (numerous)

0.3 0.1Jinniushan, ChinaJinniushan

0.2 0.05Ngandong, IndonesiaNgandong 1, 9, 10, 11

Table 1: Key Homo erectus fossil sites. A partial list of key Homo erectus fossil localities, and some of the key specimens preserved at each. Exact dates are difficult to obtain for many of these localities, so the above dates represent best approximate ranges. In some cases, such as Olduvai Gorge and Koobi Fora, fossils have been recovered from many individual localities within the area, spanning a large range of dates.

There are a number of fascinating evolutionary questions that can be asked of H. erectus. The species was not only geographically widespread, it also had a long temporal span in the hominin fossil record (Antn 2003). With its earliest appearance in the fossil record from localities in the Lake Turkana Basin, Kenya, sometime around two million years ago, H. erectus populations persisted until near the end of the Pleistocene, as evidenced by fossils from Southeast Asia. Homo erectus thus presents paleoanthropologists with the challenge of trying to interpret fossil variation in the context of both widespread geographic and temporal distribution.

Furthermore, the expansion of H. erectus across a large range of environments suggests a change in the ecology of this lineage relative to early hominins, a change that certainly has significance for how evolutionary forces acted to shape the pattern of variation we observe in the fossil lineage.

These are some of the questions that researchers ask of H. erectus fossils: How did the ecology of Homo erectus differ from that of preceding hominins? What are the characteristics of H. erectus that allowed it to expand across different habitats throughout portions of Eurasia and Africa? What limitations constrained the expansion and evolution of H. erectus in the Pleistocene? What role did behavioral and technological innovation play in establishing the complex and geographically widespread evolutionary pattern of H. erectus? How might we describe and explain the evolutionary pattern of H. erectus?

History and Geography

Eugene Dubois first identified and described a new human-like set of Indonesian fossils at the end of the 19th century, naming the specimens Pithecanthropus erectus (upright, ape-man) because of their combination of bipedality and a brain size much smaller than living humans. Dubois had specifically been looking for the missing link between apes and humans, and for him the combination of a human-like body and ape-like brain represented just that (Shipman 2002). Subsequent discoveries in the 1920s and 1930s from the site of Zhoukoudian, China, of fossils with similar characteristics-originally designated Sinanthropus pekinensis-raised the question of a possible evolutionary relationship between these regional samples. Today, these two samples, along with a much larger collection of fossils from Asia, Africa, and Europe, are most commonly referred to simply as Homo erectus.

What is the evolutionary relationship among fossils that share many similarities, but also subtle differences, separated across time and space? This question, prompted by the early Chinese and Javan fossils, remains an active research question today for the much larger sample of fossils assigned to H. erectus. Whether or not a sample from one region, for example Africa, part of a polytypic, geographically widespread lineage (Homo erectus), or whether it is part of a related, but different species, is a debated topic and reveals much about the evolutionary pattern of the species (Rightmire 1998). For example, some researchers argue that H. erectus is restricted largely to Eastern and Southeast Asia, consistent with the original fossils attributed to the taxon. In that case, the bulk of its representatives lived from the end of the Lower Pleistocene through the Middle Pleistocene (~1.4-0.2 mya). From this perspective, earlier fossils from Western Asia (e.g., Dmanisi, Georgia; Figure 2) and Africa (e.g., Koobi Fora, Kenya) that are similar to the classic Asian H. erectus, but also have more ancestral traits, might be considered a separate lineage (often called Homo ergaster). Middle Pleistocene remains from Europe might be a second or third separate lineage (Homo heidelbergensis). In this view, the ecological niche occupied by these species is more limited, leading to the isolation, and ultimately speciation, among different regional populations.

Figure 2:Cranial and mandibular fossils from Dmanisi, Georgia.

Fossils dated to roughly 1.7 million years ago, demonstrate morphological variation in Homo erectus from a single site.

2012 Nature Education Courtesy of Adam P. Van Arsdale. All rights reserved.

Humans are widespread and variable today, but much of the variation observed across contemporary populations is the result of relatively recent events in the past 100,000 years of our evolutionary history. Patterns of variation in H. erectus occurred on a time scale as long as a million years, and may have been different from those we observe today. This presents a challenge for researchers in terms of how we explain the pattern of variation seen in H. erectus, but also presents an opportunity to study how evolutionary forces operate across such scales.

Who was Homo erectus?

As with any fossil lineage, identifying the earliest appearance of the species is difficult. Nevertheless, a set of shared, derived features can be assigned to all of the fossils assigned to H. erectus, regardless of where they fall amid the geographic and temporal range of the lineage. The following sections summarize some of these characteristics.

Increased body size

One of the traits most commonly associated with Homo erectus is an increase in body size. The Nariokotome specimen, an adolescent male individual, was over five feet tall at the time of his death (Walker & Leakey 1993; Figures 3 & 4). Estimates of his adult stature, had he continued to live to adulthood, differ depending on how researchers estimate his age at death based on his teeth and bones (for more see Smith & Alemseged NKP article LINK HERE) and the amount of growth he had left. Living humans generally experience a marked increase in growth during early adolescence (i.e., a growth spurt'), a growth pattern that some researchers say distinguishes us from other apes. If early H. erectus had a human-like growth spurt, Nariokotome likely had a lot of growing left to do. Even if H. erectus did not have such a modern human-like pattern of growth, the specimen was clearly a tall individual relative to earlier hominins. Not all H. erectus were tall, however, as earlier fossils remains from sites like Olduvai Gorge in Tanzania and Dmanisi, Georgia, attest. It is important to note that variations in size, not just an increase in size over that of earlier hominins, is characteristic of H. erectus, much like living humans.

Figure 3:The Nariokotome Homo erectus skeleton (a.k.a. The Turkana Boy; KNM-WT 15000).

Dated to between 1.5 and 1.6 mya, and discovered on the western side of Lake Turkana Kenya in the mid 1980s by Kamoya Kimeu, leader of the paleontological team dubbed the 'Hominid Gang.'

2012 Nature Education Courtesy of Alan Walker. All rights reserved.

Figure 4:A reconstruction of 'Lucy' (A.L. 288-1).

A partial skeleton of Australopithecus afarensis, alongside a Homo erectus partial skeleton from the site of Nariokotome, Kenya (KNM WT-15000), to show the large size increase associated with the genus Homo.

2012 Nature Education All rights reserved.

Increased brain size/encephalization

As the body size of hominins increases, the brain size increases as well (Ruff et al. 1997). While the smallest-bodied early H. erectus fossils have brain sizes only slightly larger than earlier hominins (australopiths), early large-bodied specimens, such as the Nariokotome individual, have a brain volume greater than 800 cm3, more than 50% larger than earlier australopiths (and about 60% of the typical brain size of someone living today). However, in addition to the absolute increase in brain volume that accompanies an increase in body size, there is also a proportional increase. This is referred to as encephalization, and is an important characteristic of H. erectus. Throughout the evolutionary history of H. erectus there is substantial evidence for selection leading towards increased encephalization, so that while early members of the lineage have a cranial capacity of 600-800 cm3, the cranial capacities of most later specimens are well in excess of 1000 cm3, which is within the lower range of contemporary humans, without appearing considerably larger in body size than early H. erectus.

Increased technological/ecological intensification

The large body and large brain of H. erectus needed more energy, and thus food, than previous hominins. Larger biological structures, particularly energy-intensive ones like muscles and brains, require greater energy inputs to maintain. Thus, H. erectus is often reconstructed as occupying an intensified ecological niche (Leonard & Robertson 1997).

The intensified niche goes hand in hand with the expansion in brain and body size. Larger bodies, and longer limbs in particular, increase locomotor efficiency (Pontzer et al. 2010). Homo erectus could cover more ground on a day-to-day basis, through walking or running, than smaller hominins and with lower energy cost. In addition, the larger brain gave these hominins better capabilities for processing complex ecological information across the more expansive terrain containing higher quality food items. For example, there is clear evidence of H. erectus accessing medium- and large-sized animal carcasses for meat, through hunting and/or scavenging, in the form of fossil remains of animals with cut marks left by butchery. This behavior, regularly accessing animal carcasses, is an ecological change from earlier hominins (Link to Pobiner's NKP article). While the earliest H. erectus specimens are found in association with very basic stone tools, typically referred to as the Oldowan stone tool industry, by 1.5 million years ago populations of H. erectus were creating a more complex and typologically codified set of tools that we refer to as the Acheulean industry (Bar-Yosef & Belfer-Cohen 2001).

Reduced post-canine dentition size

The change in ecology associated with H. erectus coincides with a corresponding change in the dentition and jaws of this species. Relative to earlier australopiths and contemporary robust australopiths (Paranthropus), the size of the post-canine dentition (premolars and molars) and the molarization of the premolars are dramatically reduced in H. erectus. The corpus of the mandible (i.e., the toothless part that connects to the cranium) also displays increased gracility (i.e., slenderness), with a characteristic reduction in the relative breadth of the structure and supportive masticatory structures. Toothwear analyses suggest that across their range, H. erectus engaged in a diverse and broad diet (Ungar et al. 2006). The food an organism ingests can also produce subtle changes in the chemistry of body tissues (you actually are what you eat), including the dentin and enamel that make up the crown of a tooth. Using this information, investigations of the stable isotope chemistry of H. erectus teeth also support the idea of a flexible and diverse diet (Ungar & Sponheimer 2011). Whatever the flora and fauna H. erectus ate at the varied geographic localities where H. erectus fossils are found, their tooth and jaw anatomy reveal that their diet did not require the same robust masticatory adaptations seen in earlier hominins.

Unanswered Questions About Homo erectus

Two of the more significant, yet elusive, questions about H. erectus concern the levels of sexual dimorphism within the lineage and the capacity for language. Sexual dimorphism, the physical differences between males and females, is an important source of variation within species, and in primates can be an indicator of reproductive strategy and group dynamics. Sexual dimorphism, given its role in intraspecific variation, can also be a confounding factor in proper taxonomic identification. The large amount of size variation observed within H. erectus, taken primarily from fragmentary fossil remains, makes it difficult to estimate average levels of dimorphism. The H. erectus fossil record provides clear evidence of a large range of skeletal size variation, at least equivalent to that observed in living human populations, but it does not provide conclusive evidence that males were systematically larger than females to a greater extent than they are today. If H. erectus did have more sexual dimorphism than H. sapiens, we would infer that male competition for mates was more dependent on body size than it is today.

Language is perhaps the hallmark human trait, but can be difficult to assess directly from the fossil record. Attempts to identify language ability in the fossilized skeletal remains of H. erectus have focused on aspects of the nervous system, including the size of the vertebral canal (a proxy for the size of the spinal cord), and external features of endocasts (natural fossils of endocranial space and a proxy for brain size and shape). Thus far, there have been no definitive anatomical findings to cause researchers to reject the idea that H. erectus was capable of some kind of human-like proto-language.

More recently, arguments about the origins of language have focused on the reconstructed histories of genes associated with language production in humans. The recovery of ancient genetic sequences from Neandertals and other archaic human specimens (e.g., a specimen from Denisova Cave in Siberia, Russia) have provided new insight into the genetic history of language production. The human FOXP2 gene exists in a derived form in humans today and appears to play a critical role in language development. The identification of the human form of FOXP2 in both Neandertal and Denisovan genomes suggests this gene likely goes back at least to the Middle Pleistocene, with H. erectus a possible source lineage (although there is no H. erectus ancient DNA to test this hypothesis). This does not suggest H. erectus had well-developed language capabilities but, like the anatomical evidence, does not provide any evidence to reject the idea.

Summary

Homo erectus represents a significant transformation from previous hominins, like the australopiths, to a species much more similar to modern humans. Relative to their australopith forebears, Homo erectus was bigger, smarter, and more able to occupy and survive in differing landscapes in a changing world. The movement towards a more ecologically intense, cognitively reliant, and behaviorally malleable adaptive pattern set the stage for the evolutionary change that followed in the Pleistocene, up to and including the present. In many ways, modern humans are just an updated version of our H. erectus ancestors.

Glossary

Acheulean - Lower and Middle Pleistocene hominin stone tool industry. The Acheulean tool complex is often characterized by a high percentage of bifacially flaked stone cores and the presence of tear-drop shaped tools referred to as hand axes'.

ancestral - A trait that is present in the common ancestor of a species. The large body size of contemporary humans is ancestral, as evidenced by the presence of this feature in Homo erectus.

derived - A trait that is not present in the common ancestor of a species, but is newly arisen. The marked encephalization of Homo erectus is a derived characteristic relative to earlier, small-brained hominins.

ecological niche - The overall set of relations that defines the place of a species within its environment. This includes the other organisms a species interacts with, such as prey or predators, as well as the physical habitats a species utilizes in its existence.

endocasts - A natural fossil cast formed within the endocranial space of a skull. When present, endocasts provide some resolution on the size, shape, and surface structures of the brain in fossil taxa.

encephalization - Expansion of the brain relative to body size. Encephalization represents an increase in proportional resources dedicated to the growth, development, and maintenance of brain activities.

masticatory - Of, or relating to, the chewing structures of an organism.

Oldowan - The earliest well-characterized hominin stone tool industry, present in the terminal Pliocene and Lower Pleistocene. This tool complex is characterized by a simple core-flake set of tools.

polytypic - The presence of multiple forms of a lineage across a species' range.

sexual dimorphism - The characteristic differences between males and females within a species. Often this refers specifically to size sexual dimorphism, the average difference in body mass or skeletal size between males and females of a species.

References and Recommended Reading

Antn, S. Natural history of Homo erectus. American Journal of Physical Anthropology 122, 126-170 (2003).

Bar-Yosef, O. & Belfer-Cohen, A. From Africa to Eurasia-Early dispersals. Quaternary International 75, 19-28 (2001).

Leonard, W. R. & Robertson, M. L. Comparative primate energetics and hominid evolution. American Journal of Physical Anthropology 102, 265-281.

Pontzer, H. et al. Locomotor anatomy and biomechanics of the Dmanisi hominins. Journal of Human Evolution 58, 492-504 (2010).

Rightmire, G. P. Human evolution in the Middle Pleistocene: The role of Homo heidelbergensis. Evolutionary Anthropology 6, 218-227 (1998).

Ruff, C. B. et al. Body mass and encephalization in Pleistocene Homo. Nature 387, 173-176 (1997).

Shipman, P. The Man Who Found the Missing Link: Eugene Dubois and His Lifelong Quest to Prove Darwin Right. Cambridge, MA: Harvard University Press, 2002.

Ungar, P. S. & Sponheimer, M. The diets of early hominins. Science 334, 190-193 (2011).

Ungar, P. S. et al. Dental microwear and diets of African early Homo. Journal of Human Evolution 50, 78-95 (2006).

Walker, A. & Leakey, R. The Nariokotome Homo erectus Skeleton. Cambridge, MA: Harvard University Press, 1993.

Walker, A. & Shipman, P. The Wisdom of the Bones: In Search of Human Origins. New York, NY: Vintage, 1996.