Course:ARCL140 Summer2020/Group 6

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Descendants of Homo Erectus

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Section: ARCL 140
Instructor: Lee Elizabeth Doyle
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Contributors and Roles

Lochlan Breckenridge - Site 1

Samantha Bell - Site 2

Jacob Rauma - Site 3

Saina Adamy- Site 4

Map

Group 6 Map

Coordinates of each site:

Site 1: Liang Bua, -8.53058, 120.44371

Site 2: Johannesburg, -25.924304, 27.764887

Site 3: Gran Dolina, 42.3525, -3.5183333

Site 4: Mauer, 49.3402, 8.7990

Introduction

The origins of modern humans is understood in exploring the evolution of morphological diversity and the geographic expansion of its species. Divergence of hominins can be traced to a key point in evolutionary history—through the descendants of Homo erectus.

Homo erectus changed the global impact of hominins through its geographical expansion, anatomical evolution, and the non-selective evolutionary forces that caused unprecedented morphological diversity[1]. Due to the rapid evolution and geographical isolation of various descendants, phylogeny (taxonomy based on decent relationships) is challenging and emphasizes the process of mosaic evolution. As argued by Alan Turner and Andrew Chamberlain in their paper Speciation, morphological change and the status of African Homo Erectus, "this limited degree of necessary correlation between morphological change and speciation renders attempts at species definitions based on autapomorphic character states difficult."[2]

This project explores four descendants of Homo Erectus: Homo floresiensis, Homo naledi, Homo antecessor, and Homo heidelbergensis and identifies the sites that each were discovered and how they contribute to the evolution of Hominins.

Homo floresiensis was discovered on the isolated island of Flores in 2003, and appears to be descended from Homo erectus individuals that migrated to the island. However, the species appears to have undergone insular dwarfism in response to a lack of predators and a low amount of food on the island, which indicates that the genus Homo has a more variable and adaptable anatomy than once thought.[3]

Homo naledi has physical features similar to other homo, yet is uniquely distinct and defies known anatomical evolution. Evidence on site even indicates Homo naledi may have developed cultural practices. These features challenge assumptions of the evolution of hominins and make it difficult to confirm the decent relationship, but dating connects it with other descendants of Homo erectus.[4]

Homo antecessor was originally discovered in 1991 at the Gran Dolina archeology site in the Sierra Atapuerca mountain range in northern Spain. Research suggests that this species represents the oldest European extinct lineage, different from other African lineages, and closer to Asian hominins. Much still needs to be discovered about Homo antecessor, but scientists believe that Homo antecessor is a distant relative to modern Homo sapiens.[5]

Homo heidelbergensis was first discovered in Mauer, Germany, on October 21, 1907. A single lower jaw was found in the fluvial sands deposited by the Neckar River nearby the south-east of Heidelberg, Germany. Homo heidelbergensis are regarded as the common ancestor of modern humans and Neanderthals and their presumed ancestor was Homo erectus.[6]

Site 1: Liang Bua

Author: Lochlan Breckenridge

Location: Liang Bua Cave, 14 km North of the city Ruteng on the island of Flores, Indonesia. -8.53058, 120.44371

Age: 100 000 - 60 000 years old (Late Pleistocene)[7]

Context

Liang Bua Cave is a limestone cave located in the Wae Racang river valley on the island Flores in Indonesia. Deposits in the cave are dated to the Late Pleistocene, between 95 and 14 thousand years old.[7] Flores is covered with tropical rainforest, and before the arrival of modern Humans, the island was home to animals including Komodo dragons and dwarf elephants, along with a small-bodied human species named Homo floresiensis. In the Pleistocene, Flores had no large predators with the exception of Varanids and relatively few foods that humans could eat.[3]

Flores can only be reached by travelling over water. It is not believed that there were any land bridges between Flores and any other islands, or between Flores and mainland South East Asia, during the Pleistocene.[3] As a result, any animals colonizing the island, including Hominins, would have needed to travel across the sea to reach it, and would subsequently be unable to leave the island without making a similar journey. It is hypothesized that being trapped on an island with limited resources can lead to insular dwarfism, the process by which island-living animals become smaller than their relatives on larger landmasses.[3] On islands with less food, few predators, and low interspecific competition, natural selection can favour smaller bodies.[3] Flores was once home to the dwarf elephant Stegodon florensis insularis that exemplifies this evolutionary process, and it is believed that Homo floresiensis' small body size can be explained by insular dwarfism.[3][8]


History

The first excavations in Liang Bua cave occurred in the 1950s and 1960s, but the discovery of Homo floresiensis did not occur until September 2003. A joint team of Indonesian and Australian researchers found remains of two individuals, named LB1 and LB2. The bones had been covered with sediment but none of them had fossilized, so they were very fragile. LB1 was relatively complete, including a cranium, mandible, right leg and left innominate, with some fragments of other bones. [3] Based on the pelvis, LB1 was determined to be a female, but the individual was unexpectedly small.[3] In addition, the individual had a very small brain, with a brain to body size ratio more similar to that of Australopithecines than most members of Homo.[3]

Numerous explanations for the small size and abnormally small brain of LB1 were proposed, including the idea that the individuals were modern humans with microcephaly.[8] However, the bones show insufficient evidence of microcephaly and lack features associated with Homo sapiens such as a chin, so the most popular hypothesis is that the individuals are members of a distinct species that had undergone insular dwarfism and had descended from Homo erectus or a similar Homo species. [8]

The analysis of the original bones from Liang Bua also sparked some controversy, as some of the bones were damaged after being taken to the personal laboratory of a scientist not involved in the discovery. A pelvis was damaged, and a lower jaw had been glued back together improperly while in the care of palaeoanthropologist Teuku Jacob.[9] The damage these bones endured resulted in a significant uproar in the scientific community.

Relevance

The unique morphology of Homo floresiensis demonstrates how adaptable the Homo genus can be. While human species often use cultural and behavioural adaptations to survive in new environments, anatomical changes appear to be just as important in the story of hominin evolution. In addition, the dates of Homo floresiensis' fossils suggests this species was relatively successful, persisting into the late Pleistocene even after Homo Erectus had gone extinct.[7] Homo floresiensis may even have survived until the arrival of Homo sapiens in Flores, as the last known fossils of Homo floresiensis date to around 60 000 years ago and some stone artifacts date to 50 000 years old, while evidence of Homo sapiens in Indonesia dates to around 50 000 years ago.[7]

The existence of Homo floresiensis also suggests that their ancestors, whether they were Homo erectus or a related species, reached the island by travelling over open water. It is not known whether these humans made this trip intentionally (perhaps by making a raft or boat) or unintentionally (perhaps by being swept out to sea by a storm, clinging on to a natural raft). Regardless, the arrival of humans on Flores indicates a high degree of mobility and adaptability.

Site 2: Johannesburg

Author: Samantha Bell

Location: Rising Star cave system (UNESCO Cradle of Humankind site), Johannesburg, South Africa

Age: between 236,000 and 335,000 years old[10]

Context

Within an extensive world heritage site, northwest of Johannesburg, South Africa, lies a complex of limestone caves where some of the first hominid fossils were discovered. Since the discovery of the first Australopithecus in 1936[11], this site has continued to produce important samples of hominid remains for nearly a century. The geological conditions, limestone and other sediment caves, explain why the remains of a species that lived all over the continent and world are concentrated within the site. Cool temperatures and protection from climatic events have allowed for the preservation of an array of remains dating back millions of years. The landscape of the area, “with caves and water resources provided a setting favored by many animals including hominids.”[12] also explains why so many fossils have been found here. Millions of years ago, it would have been alive with flora and fauna due to an ecology that supported such vibrant life.

The Rising Star cave system is located just 800 meters outside of the heritage site and is home to the Dinaledi Chamber. In order to reach this portion of the cave, a series of narrow and vertical passageways are traversed, one section as narrow as 20 centimeters. This excruciatingly difficult access to reach the chamber is the cause for both the preservation and recent discovery of the bones. Cave deposits and sediment traps collected fossils and provide a glimpse into the Pleistocene ecosystem and how it evolved as climate and landscape changed.[13]

History

The 2013 discovery and following excavation of the Dinaledi Chamber produced hominin previously unknown, named Homo naledi. The unique geological conditions of the Dinaledi chamber explain the preservation of the fossils: difficult to reach, dark, and remote. The fossils were found in mud-rich sediments far inside the cave by a group of cave explorers contracted by palaeoanthropologist Lee Berger. An excavation team, lead by Berger, revealed extraordinary fossils that have characters of the genus Homo, yet challenged assumptions of the Homo evolution. The group applied modern technologies in order to excavate the remote site, like white light scanners and 3D mapping. In total, over 1681 bones that represented at least 18 individuals were found—more than any other excavation in the world.

The subsequent study of the many complete fossils and skulls, revealed a mystery within the homo genus. Its brain was approximately one third the size of a modern human. Its shoulders and chest were ape-like, the spine was small and resembled Neanderthal spines. The arms were human like, except for curved fingers which date back millions of years to ancient human relatives. When dating techniques used by the team suggested that Homo naledi was estimated to be 335,000 to 236,000 years old[4], rather than the millions of years that the anatomy might suggest, it puzzled the scientific community.

However, it wasn’t just the anatomy that was cause for confusion. The location of the fossils, deep inside the cave, suggests intentional placement of the remains, which further suggests a burial ritual. Deliberate placement of the dead, up until the moment Homo naledi was discovered, was thought to be a modern human practice. The suggestion of the cultural practice coming before modern humans is extraordinary. It challenges what scientists think they know about the origins of culture and what else remains to be discovered.

Relevance

The Dinaledi Chamber fossil site revealed a hominid that launched paleoanthropologists into disputed identification and classification. In 2015 Jamie Shreeve, for National Geographic, reported that the discovery was amazing, “but their scientific value remains in limbo until we know how old they are.”[14] Recent technological dating of Homo naledi to only a few hundred thousand years challenges previous anatomical taxonomy. Homo naledi has features similar to other homo, yet is uniquely distinct and defies known anatomical evolution. The presumed intentional placement of the bones deep inside one of the hardest to reach chambers within a challenging cave system indicated culture, thought to have only developed in more modern humans. Current phylogeny suggests that Homo naledi is a descendant of Homo erectus, despite previously unassociated characteristics. With unexpected combinations of characteristics and challenges to assumptions of the evolution of hominins, Homo naledi causes scientists to re-examine their beliefs and expand understanding of the mosaic evolutionary process.  

Site 3: Gran Dolina

Author: Jacob Rauma

Location: Sierra de Atapuerca mountain range, Northern Iberian Plateau, Spain

Age: 800,000 – 1.2 Million years old

Context

The Sierra de Atapuerca mountain range is located in the northern Iberian Plateau in Spain. The range is a gentle sloping highland that is about 10 km long and slightly less than 2 km wide. The mountain range contains a rich variety of karstic cavities and fissures within Cretaceous limestones and dolomites[5]. The “Gran Dolina” site in the Sierra de Atapuerca range is an 18-meter-thick sedimentary sequence that has been divided into 11 stratigraphic units named TD1 – TD11, where several hominin occupations have been identified.[5] Several other caves within the mountain range have been found since the 1980’s that also contain significant archeological finds as well. The site, since its discovery, has produced thousands of fossils and artifacts that have become a Pleistocene landmark in studies of early human settlement outside of Africa. The Sierra de Atapuerca archeological complex was added to UNESCO’s World Heritage List in 2000 and has since become a key Eurasian paleoanthropological locality.[5]

History

Homo antecessor was originally discovered in 1991 at the Gran Dolina archeology sight in the Sierra Atapuerca mountain range in northern Spain.[5] The highly complex Atapuerca cave systems were discovered in the mid 19th century when a railway trench was inserted into the ground. The large-scale archeology project that has unearthed myriad of fossils began in 1978 and continues to this day. Around 20 years after the project began in 1994 & 1995, more than 80 bone fragments belonging to six individuals, along with 200 stone tools and 300 animal bones were discovered. All of the fossils were dated to be at least 900,000 years old.[5]

Since the initial project in 1994, the excavation front has changed considerably due to ongoing field work. Since then, an additional 13 m have been opened up for excavation, thus providing ideal opportunities to expand the search for additional clues to who Homo antecessor really was. At present date, 150 Homo antecessor fossil remains, belonging to approximately 11 individuals have been discovered.[5] Significant among these fossils is an almost complete left half mandible, a complete cranium, a complete pelvis (humorously named “Elvis”) and the remains of a child with craniosynostosis.[15] The latter discovery is considered to provide evidence for food sharing in early human populations. The significance of such a find is that it suggests this species represents the oldest European extinct lineage, different from other African lineages, and closer to Asian hominins.[15] Additionally, fifty footprints dating to between 1.2 million and 800,000 thousand years ago were also discovered in Happisburgh, England. Archeologists suspect these footprints also belonged to Homo antecessor groups, thus bolstering the proposition that this is the oldest extinct European lineage ever discovered.[16]

Relevance

Scientists are still searching for the last common ancestor modern humans had with Neanderthals and Denisovans, the three of the most modern human lineages. In fact, when originally discovered, archeologists believed that they could have been that exact missing link, as Homo antecessor had an interesting mix of both ancient and modern facial characteristics. For example, Homo antecessor had cheekbones that were strikingly similar to those of modern Homo sapiens. However, with more advanced scientific methods, researchers were able to examine the unique sequences of amino acids that made up the proteins of their bodies – a technique that allowed researchers to circumvent the need to find viable DNA vestiges in the fossils. The conclusion was that Homo antecessor was not actually a precursor to Homo sapiens, but more so a distant relative with many similar characteristics.[17] As the project at the Gran Dolina expands, so too will our understanding of our extinct European relatives, but for the time being, there is much to be discovered about who they were, and where we come from.

Site 4: Mauer

Author: Saina Adamy

Location: Mauer, 10 km south of Heidelberg, Germany, 49.3402, 8.7990

Age: Between 300 000 to 700 000 years old

Context

Mauer is a site located 10 km south of Heidelberg, Germany. A single lower jaw called the “Mauer jaw” was found at a depth of 24 m in the Grafenrain sandpit, resting in the fluvial sediments of “Mauer sands”[6], on October 21, 1907. The Mauer sands are subdivided into two units: the “lower sands: and the “upper sands”, which are divided by a clay layer (the “Lettenbank”) and were deposited by the Neckar River. The mandible of Homo heidelbergensis was discovered within the lower sands at a 0.1-m-thick gravel layer[6]. The lower sands and the upper sands are known to have warmer climate conditions indicated by their rich early Middle Pleistocene mammal fauna; they also witnessed two Middle Plesitocene interglacial stages. Mammal bones, especially the human mandible, were preserved well and indicates that they were transferred from a fluvial floodplain nearby before being embedded in the river deposits; they share the same geological age as the sediment layers they are surrounded by [6]. The Mauer sands are covered by many Middle and Late Pleistocene glacial loess layers with interstratified interglacial paleosol horizons- this forces the age of the fossil to be older than ca. 350 ka [6]. The "Mauer jaw" that was found at this site is estimated to be around 600 000 years old [18].

History

Mauer is notably the site where the first remains of Homo heidelbergensis were discovered. The first finding was a single jaw was found and it was estimated to be about 600 000 years old [18]. An important feature of this jaw was that it had an unusually thick raumus; the vertical projection that links to the skull[18]. Other distinctive features were its thick brow ridge and large face. These skulls housed larger brains than Homo erectus, ranging about 1200 cubic centimeters[18]. Their brain size was close to what the size modern human brains are, which range about 1400 cubic centimeters. Homo heidelbergensis individuals were also physically the most massive-bodied in the human fossil record [19]; they were strong-boned and powerfully built. Their shoulders were more modernized and more forward facing than early hominins. Changes in the pelvis allowed the birth canal to be widened so that a larger-brained fetus could pass through[19].

Studies proposed that the larger brains in Homo heidelbergensis was reflected in the complex tools they developed, such as wooden spears. Although they used the same material for tools as Homo erectus, they added significant improvements in the way they were made. One tool method Homo heidelbergensis invented involved shaping a tool while it was still attached to the stone core- the result of this would be the finished tool. This method allowed tools to have maximum edge per unit of weight and an advanced visualization of the tool. Stone tools were also being manufactured with soft hammers, usually made of wood, to produce thinner, sharper flakes. Members of Homo heidelbergensis were capable of hunting horses, rhino, and large deer[19].

Relevance

These remains serve as an important component when studying and understanding early human occupation in Europe and north of the Alps[6]. After several techniques used to study their findings, their results demonstrate that the Homo heidelbergensis mandible is the oldest hominin fossil reported to date from central and northern Europe[6]. These results raise questions relating to the physical relationship of Homo heidelbergensis and older populations that were reported from southern Europe and Africa. It is also important to note that Homo heidelbergensis developed new stone tools methods which suggested advances in spatial cognitions, nearly to modern levels [19]. Their unique tool-making techniques and methods using materials they already had suggest advances in cognition. These improvements and new methods helps us trace back to how they lived, how they evolved, and whether they are related to our common ancestors. They are seen as a pivotal figure during the evolution period and regarded by many as the common ancestor of modern humans[18].

Conclusion

The story of Homo erectus is a unique one, as it was one of the most successful and widespread human species in history. This hominin migrated out of Africa and throughout Eurasia, exemplifying their adaptability by diversifying into new forms and developing new ways to cope with changing surroundings. In addition, the cognitive advances and complex taxonomy of archaic humans make the origins of our own species more difficult to determine. The discovery of Homo floresiensis indicated just how far Homo erectus explored, venturing to remote islands where their descendants would be selected for dwarfism. Homo naledi made it clear that the traits of modern humans did not evolve all at once, rather traits overlapped in a mosaic of old and new present in different human species. In addition, scientists are still searching for the last common ancestor modern humans had with Neanderthals and Denisovans. When first discovered, H. Antecessor was considered to be the possible missing link, as they possessed strikingly similar features of modern H. Sapiens. However, archeologists soon realized that they were not our last common ancestor, but a distant relative of modern H. sapiens.Instead of providing information of the elusive link between archaic and modern H. Sapiens, H. Antecessor has provided archeologists with a wealth of information regarding the first lineages of hominins to ever set foot in Europe. The discovery of Homo heidelbergensis was an important step in understanding human evolution. Although they used the same materials for their tools as their earlier ancestors such as Homo erectus, they invented new methods of manufacturing them. This aspect is important to note because it indicates advances in cognition; Homo heidelbergensis'brains were advanced in ways closer to our own. These early humans teach us that determining who our ancestors were will continue to be a difficult process, as species that seem to look and act like our own may not have given rise to us. The ancestor of all of these unique hominins is Homo erectus, the species that explored the world and diversified into remarkable forms long before our species walked the earth.

Bibliography

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  2. Turner, Chamberlain, Alan, Andrew (April 1989). "Speciation, morphological change and the status of African Homo erectus". Journal of Human Evolution. 18: 115–130 – via Elsevier Science Direct.
  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Brown, P.; Sutikna, T.; et al. (October 2004). "A New Small-Bodied Hominin from the Late Pleistocene of Flores, Indonesia". Nature. 431: 1055–1061. Explicit use of et al. in: |last3= (help)
  4. 4.0 4.1 Dembo, Radovčic, Garvin, Laird, Mana, Davorka, Heather M., Myra F.; et al. (August 2016). "The evolutionary relationships and age of Homo naledi: An assessment using dated Bayesian phylogenetic methods". Journal of Human Evolution. 97: 17–26 – via Elsevier Science Direct. Explicit use of et al. in: |last= (help); Explicit use of et al. in: |first= (help)CS1 maint: multiple names: authors list (link)
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 "Reassessing the age of Atapuerca-TD6 (Spain): new paleomagnetic results" (PDF). Research Center for Human Evolution (CENIEH).
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  12. Dirks, Paul (February 2013). "Hominin-bearing caves and landscape dynamics in the Cradle of Humankind, South Africa". Journal of African Earth Sciences. 78: 109–131 – via Science Direct.
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  14. Shreeve, Jamie (September 2015). "New Human Ancestor Elicits Awe—and Many Questions". National Geographic.
  15. 15.0 15.1 "Craniosynostosis in the Middle Pleistocene human Cranium 14 from the Sima de los Huesos, Atapuerca, Spain". PNAS.
  16. "Hominin Footprints from Early Pleistocene Deposits at Happisburgh, UK". PLOS ONE.
  17. Scharping, Nathaniel (April 1, 2020). "An Ancient Tooth Is Revealing More About Our Human Ancestors". discovermagazine.com.
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  19. 19.0 19.1 19.2 19.3 Gurche, John (2013). "A SYMBOLIC ANIMAL: Homo heidelbergensis (0.7 to 0.2 million years ago). In Shaping Humanity: How Science, Art, and Imagination Help Us Understand Our Origins". Yale University Press.