Course:ARCL140 Summer2020/TermProject_Group12
Contributors and Roles
Contributors: Francesca Ciocca, Taylor Swift-LaPointe, Alina Cook, Alicia Iachetta.
Roles: Francesca conducted research for and wrote the Taung Child Type site, Taylor conducted research for and wrote the Gona Pelvis site, Alina conducted research for and wrote the Hadar formation site. Alicia created the wiki page and uploaded all information to it, found and uploaded images as well as the google map, and helped edit work. All group members contributed to the introduction and conclusion.
Introduction
Birth, the moment in which new life is brought into the world, is a fascinating and complex topic within human evolution. The human pelvis and childbirth are significantly different than in other non-human primates (Gruss and Schmitt 2015). For example, modern humans birth babies that are 6% of their body mass, whereas chimpanzees birth babies that are only 3% of their body mass (DeSilva 2011). The process of human birth was likely affected by several major trends in the evolution of early hominins. Both the anatomy of the female pelvis, as well as that of the baby, would have undergone significant changes as our ancestors shifted from arboreal life to increased bipedalism. The mechanics of walking on two feet required a reduction in birth canal size (Gruss and Schmitt 2015). Additionally, neonatal brain size increased from primates to Australopithecus to Homo erectus to Homo sapiens, causing additional challenges to parturition (DeSilva 2011). Moreover, childbirth would have had to evolve to accommodate other features that were evolving, such as broader shoulders and a larger brain. Therefore, childbirth is undoubtedly important to the study of human evolution, because it occurred in conjunction with, and possibly due to other adaptations such as bipedalism, brain size, and shoulder width that lead to the evolution of modern humans.
Discoveries at the Taung Child Type Site, the Gona Pelvis Site, and the Hadar Formation Site have led to insights regarding childbirth in early hominins. The Taung Child fossil, discovered in Taung, South Africa, provides insight into the process of parturition. This Australopithecus africanus specimen was thought to display an early form of the delayed cranial suture fusion seen in modern humans (Falk et al. 2012). This would improve skull flexibility during birth and brain development afterwards. However, later studies refuted the presence of unfused sutures in the Taung Child, and claimed that australopiths would have encountered less difficulty during birth than later hominins (Holloway et al. 2014). The Gona Pelvis site from Gona, Ethiopia is the first complete Homo erectus pelvis found (Simpson et al. 2008). The female pelvis is extremely wide, and its “capacious birth canal” suggests increased pelvic sexual dimorphism and the possibility of birthing large-brained babies (Simpson et al. 2008). The Hadar Formation, located in Ethiopia, is a site abundant in fossils dating back 3.45 million years (Campisano 2012). Notably, a fossilized member of Australopithecus afarensis, better known as Lucy, was found at this site, whose pelvis has contributed to the study of child birth in early hominins (Johanson 2017). Lucy’s pelvis has demonstrated how childbirth changed with other evolving factors such as broad shoulders and increased brain size (DeSilva et al. 2017). Together, these fossils highlight how pelvis and infant morphology shaped the evolution of childbirth in early hominins.
Taung Child Type Site
AUTHOR: Francesca Ciocca
LOCATION: Taung, Republic of South Africa, 403 km southwest of Johannesburg. 27.5518° S, 24.7662° E
AGE: ~2.8 million years BP
Context
The Taung Type Site is at the Buxton-Norlim Limeworks (BNL), 15 km southwest of Taung in northwest South Africa. The Thabasikwa River wraps around one side of the BNL area, which sits at the southeast edge of the Kalahari savannah (Hopley et al. 2013). It is rich in limestone (tufa) deposits from the Kalahari escarpment (Hopley et al. 2013). There are three main types of sediment recognized at the Type Site: reddish-brown or pink coloured claystone and siltstone, yellowish-red sandstone and siltstone, and tufa limestone (Kuhn et al. 2016). It is about 2.8 million years old, based on the geological age of the older pink-coloured deposit (Hopley et al. 2013); however, its age is still debated due to the variety of geological features present. The site was once part of a cave system, although it likely contains some open-air deposits and was also subject to erosion by the shifting river (Kuhn et al. 2016). Apart from a Pliocene hominin (Taung Child), other fossil finds within these cave networks include terrapins, avian egg shells, and baboons, some of which may have come from ancient limestone pools (Kuhn et al. 2016). An analysis of dental microwear in fossil baboons points to increasing replacement of forested areas with open grassland and shifting food resources in the late Pliocene (Williams and Patterson 2010). We can infer that australopiths inhabiting South Africa during this period (such as the Taung Child) would have benefited from behavioural and dietary flexibility.
History
The site was discovered in 1924 through quarry work at the Buxton-Norlim Limeworks, just outside the town of Taung (Kuhn et al. 2016). This revealed its first and most famous fossil find - the Taung Child. The specimen was described by Raymond Dart in 1925, after which a number of expeditions were made by anthropologists to investigate the Taung Child Type Site as well as other surrounding sites (Kuhn et al. 2016). Notably, Frank Peabody and Charles Camp studied the Type site and the rest of the BNL in 1947-48, uncovering additional archaeological sites in the area (Kuhn et al. 2016). It is now a UNESCO World Heritage Site, and is the location of ongoing paleoanthropological and geological studies.
Relevance
The most significant find at Taung is considered to be the skull of the young australopithecine individual (Taung Child). The fossils recovered included the face and mandible as well as a natural endocast of the skull (Falk et al. 2012). The 2.8 million year old specimen was not only the first of its species, Australopithecus africanus, to be discovered, but also the first early hominin found in Africa. Many anthropologists believe Au. africanus to be a direct ancestor of our lineage, Homo (Laitman 1986). The Taung Child was estimated to be 3-4 years of age at death, and their age at death provided some insight into the implications for brain size and obstetric challenges during birth. Cranial sutures, joints that divide the skull bones in newborns, are known to facilitate skull flexibility during birth and growth of the brain thereafter. Suture fusion occurs soon after birth in African great apes, but is delayed in modern humans (Falk et al. 2012). One study of the Taung Child endocast found the metopic suture (MS) to be only partially fused at 3-4 years of age (Falk et al. 2012). This implies that Au. africanus represents an early stage in the evolution of delayed MS fusion (Falk et al. 2012). Delayed suture fusion may have been a response to the narrowing of the birth canal (as a result of bipedalism) in conjunction with the increasing brain size of babies (Falk et al. 2012). The need for both larger brains and bipedalism in a changing landscape, and consequent biomechanical constraints on the pelvis, could have acted as a selective pressure for a more malleable skull during birth. However, another study did not find evidence of an unfused MS, and argued that the obstetric dilemma would only have become an issue in later hominins when brain size increased more significantly (Holloway et al. 2014). It is believed that australopiths experienced fewer difficulties in regards to birth canal size and newborn brain size than modern humans (Holloway et al. 2014). Nevertheless, this Pliocene hominin fossil serves as a good comparison to the skull morphology of great apes and modern humans. The Taung Child points to potential challenges that early hominins faced during childbirth, and is undoubtedly an important piece in the mosaic of human evolution.
Gona Pelvis Site
AUTHOR: Taylor Swift-LaPointe
LOCATION: Gona, Afar Regional State, Ethiopia. 11.0999° N, 40.5334° E
AGE: 1.4 - 0.9 million years BP
Context
The ‘Gona Pelvis’ site is located in the Busidima Formation, Gona, in the Afar Regional State of Ethiopia (Simpson et al. 2008). The Afar basin is part of the African Rift Valley, where tectonic activity including rifting and volcanism has occurred since the early Miocene (Quade et al 2004). The Busidima Formation is made up of the top 80m of the Hadar Formation, bordered by the Kada Gona, northern Awash, Asbole and Busidima Rivers. Both the Busidima and the Hadar Formations are exposed east of the As Duma Fault line. The Hadar Formation spans from approximately 3.4 to 2.9 million years before present, and has been the site of many fossil finds, including Australopithecus afarensis (Quade et al. 2004). The Busidima Formation has been dated 2.7 to <0.6 million years before present and is characterized by major erosion from the drying of a lake, and deposition of sand and floodplain silts (Quade et al. 2004). Many Oldowan tool artifacts have been found, including the oldest stone tools dating to 2.6-2.5 million years ago. In addition, Acheulean tools and fossils attributed to Homo erectus, including the ‘Gona Pelvis’, have been discovered (Quade et al. 2004; Simpson et al. 2008). Dating of the sediments surrounding the ‘Gona Pelvis’ together with the presence of Acheulean tools have led researchers to determine that the ‘Gona Pelvis’ site dates to the early Pleistocene period, from 1.4 to 0.9 million years ago (Simpson et al. 2008). “Analysis of carbon and oxygen stable isotopes from [soil] carbonates and herbivore enamel” at the stratigraphic level of the ‘Gona Pelvis’ site were used to hypothesize that it was a semi-arid savannah, covered by 60% grasses (Simpson et al. 2008; Quade et al. 2004).
History
The ‘Gona Pelvis’ site discovery was reported by Simpson et al. in 2008. Its discovery was part of the Gona Paleoanthropological Research Project study, which aimed to document early human evolution and the development of stone tools (de Lumley et al. 2018; Simpson et al. 2015). Extensive research of the Hadar Formation and the lower Busidima Formation has yielded Australopithecus afarensis fossils, Oldowan and Acheulean stone tool artifacts, and Homo erectus fossils (Quade et al. 2004).
Relevance
Simpson et al. (2008), reported the discovery of an adult female Homo erectus pelvis from the Busidima Formation in Gona, Ethiopia. The fossil consists of large fragments of the sacrum, both os coxae (hip bones), and the “first complete pubis from the early Pleistocene." It was reconstructed using mirror imaging of the iliac blades to produce a “nearly complete” pelvis (Simpson et al 2008; Ruff 2010). The researchers attributed the fossil to the species Homo erectus based on sediment dating, the presence of Acheulean tools, and previous discoveries of Homo erectus fossils in the Afar region at similar stratigraphic levels (Simpson et al 2008; Churchill and Vansickle 2017). However, there has been uncertainty in this initial attribution based on the fossil’s shorter stature than what was previously believed characteristic of Homo erectus (Ruff 2010; Churchill and Vansickle 2017). The fossil was determined to be female based on the comparison of morphological features to the modern human female pelvis (Ruff 2010).
The pelvis displays both basal characteristics found in other early Homo specimens and derived characteristics. Basal characteristics include “a transversely broad pelvis with laterally flaring ilia” bones, “small auricular surface, and a medially positioned pubic tubercle," and derived characteristics include a “sigmoid shaped iliac crest” and “expanded retroauricular area” (Churchill and Vansickle 2017). The significance of this pelvis is its large width of 288mm, which is more than 20mm wider than previously discovered pelvises (Ruff 2010). The birth canal size suggested the ability to birth babies with brains of about 34-36% of adult brain size (Simpson et al 2008; Churchill and Vansickle 2017). Modern human baby brains are on average 28% of adult brain size, and babies exhibit secondary altriciality, as they are completely dependent on their mothers for survival immediately upon birth (Churchill and Vansickle 2017). Most of their brain growth and development occurs after being born (Doyle 2020). The large size of this Homo erectus pelvis suggests that perhaps infants did not have the same degree of secondary altriciality as modern human babies (Churchill and Vansickle 2017). From joint size and femoral length, this Homo erectus female is estimated to have been approximately 120-146 cm in height, which is significantly shorter than other Homo erectus fossils (Ruff 2010). Simpson et al (2008), conclude that “this individual’s short stature with a capacious birth canal and characteristically female pelvic shape," is indicative of increased pelvic sexual dimorphism resulting from delivering “large-brained offspring."
Hadar Formation Site
AUTHOR: Alina Cook
LOCATION: Hadar, Ethiopia. 11.0596° N, 40.35262° E
AGE: ~3.45 million years BP
Context
The Hadar Formation, found in Ethiopia, is approximately 3.45 million years old (Campisano 2012). The formation is composed of four regions, and spans approximately 65 km2 (Campisano 2012). The site is approximately 150m thick due to layers of sediment building up over time (Johanson 2017). Currently, the Hadar Formation consists of mudstones, siltstones, fine-grained sandstones and volcanic tuffs, with sediment forming at a rate of 30cm every thousand years (Campisano 2012; Johanson 2017). By analysing fossilized plant remains found in the Hadar formation, researchers have determined the environments that existed there in the past were a forested region with abundant rainfall and another region of grassland (Johanson 2017). In comparison, a different region was an open area with little rain and many species such as bovids (Johanson 2017). The variation in environment of regions in the same vicinity is plausible, due to the effects that rivers and lakes present at the time had on the ecosystem (Reed 2008). The rivers and lakes affected the vegetation that grew near the shore, resulting in adjacent environments that were drastically different from one another (Reed 2008). Moreover, the geology of the Hadar Formation is primarily due to sediment deposits from the rivers and lakes present at the time (Reed 2008).
History
The Hadar Formation was found in 1973, once researchers realized that Ethiopia was an unexplored region that was likely to be rich in fossils (Johanson 2017). The first fossil to be found was a 3.4 million-year-old knee joint, which along with other fossils were sufficient evidence of bipedalism in early humans (Johanson 2017). Following research studies at the Hadar Formation resulted in the discovery of 370 members of Australopithecus afarensis, one species of Homo, and 7571 vertebrate organisms (Reed 2008). Notably, in 1974, the 3.2 million-year-old fossil known as Lucy, a member of Au. afarensis, was found (Johanson 2017). This fossil, found 40% complete, has been an important source for understanding the anatomy and development of early humans (Johanson 2017; Kimbel et al. 1994). Although the past environment of the Hadar Formation varied drastically, Au. afarensis was found throughout the whole region due to their ability to inhabit a wide range of environments (Johanson 2017).
Relevance
Researchers analysed the pelvis of Lucy, a member of Au. afarensis, and found that Au. afarensis gave birth in a semi-rotational oblique method (DeSilva et al. 2017). This differs from the birthing process in non-human primates which give birth with no rotation, and modern humans which have fully rotational births (DeSilva et al. 2017). In most non-human primates, the pelvis expands for the infant to orient itself and exit the birth canal such that the front of the baby’s head and body face the same way as the mothers (DeSilva et al. 2017). This adaptation allows the mother to assist with her own delivery safely (DeSilva et al. 2017). However, after analysing Lucy’s pelvis, researchers determined that some rotation during birth in Au. afarensis was necessary, due to the infant’s broad shoulders (DeSilva et al. 2017). In Au. afarensis, the head of the baby exits the birth canal, then it rotates its head and shoulders to fully exit the birth canal (DeSilva et al. 2017). In comparison, modern humans have fully rotational births to accommodate for the infant’s large brain and wide shoulders (DeSilva et al. 2017). Although Au. afarensis does not have a fully rotational birth like in modern humans, this discovery of Lucy’s semi-rotational birth highlights how childbirth was different in early humans compared to their ancestors. The evolution of a non-rotational birth in non-human primates, to a semi-rotational birth in Au. afarensis, to a fully rotational birth in modern humans demonstrates how childbirth evolved in conjunction with other important characteristics of human evolution, such as broad shoulders and a larger brain.
Conclusion
The Taung Child Type Site, the Gona Pelvis Site, and the Hadar Formation Site have all provided valuable information about the evolution of childbirth in human primates. Childbirth has evolved in association with several characteristics important to hominin evolution such as encephalization, bipedalism, and broadening of shoulder size.
In Taung, South Africa, the Taung Child fossil was not only the first find of its species, Au. africanus, but also facilitated new morphological studies on the early australopithecine cranium. The skull morphology of the Taung Child has been a somewhat contentious subject of research, but regardless of whether its cranial sutures are fused or unfused, the fossil has demonstrated how movement through the birth canal has changed as well as the extent of postnatal brain development in Au. africanus. The challenges that this species faced during childbirth, or lack thereof, inform us about the changes in hominin parturition over time. The female pelvis from Gona, Ethiopia was the first recovered nearly complete Homo erectus pelvis from the early Pleistocene period. The fossil’s large width indicates the ability to birth even larger-brained babies than modern humans. The estimated height of the individual is significantly shorter than previously discovered Homo erectus fossils, suggesting the pelvis width is due to increased pelvic sexual dimorphism rather than larger body size. Expeditions at the Hadar Formation Site in Ethiopia resulted in the discovery of Lucy, a member of Au. afarensis, which has provided insights to anatomy and development as well as childbirth in early hominins. Analysis of Lucy’s pelvis has allowed researchers to better understand how childbirth changed in conjunction with other important characteristics, such as an increased brain size and broader shoulders. Childbirth evolved from non-rotational in non-human primates, to semi-rotational in Au. afarensis, to fully rotational in modern humans. These changes in birth rotation reflect other features that evolved, and ultimately contributed to the characteristics present in modern humans.
Important evolutionary changes in hominins such as increases in brain size, broadening of shoulders, and bipedalism, led to changes in female morphology. The pelvis size increased, while the birth canal narrowed, and childbirth evolved from non-rotational to fully rotational. Modern humans today have babies with features such as larger brains, which reflect characteristics that have been passed down from early hominins to modern Homo sapiens.
References
Introduction
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DeSilva, Jeremy M. 2011. A shift toward birthing relatively large infants early in human evolution. Proceedings of the National Academy of Sciences of the United States of America 108, no. 3:1022-1027.
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Johanson, Donald. 2017. The paleoanthropology of Hadar, Ethiopia. Comptes Rendus Palevol 16, no. 2:140-154.
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Taung Child Type Site
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Gona Pelvis Site
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Hadar Formation Site
Campisano, Christopher J. 2012. Geological summary of the Busidima formation (Plio-Pleistocene) at the Hadar paleoanthropological site, Afar Depression, Ethiopia. Journal of human evolution 62, no. 3:338-352.
DeSilva, Jeremy M., Natalie M. Laudicina, Karen R. Rosenberg, and Wenda R. Trevathan. 2017. Neonatal shoulder width suggests a semirotational, oblique birth mechanism in Australopithecus afarensis. The Anatomical Record 300, no. 5:890-899.
Johanson, Donald. 2017. The paleoanthropology of Hadar, Ethiopia. Comptes Rendus Palevol 16, no. 2:140-154.
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All photos, except Google Map photo, taken from Wikimedia Commons with Author credited.