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Information about humanorigins

Published on January 21, 2008

Author: Michela


ANT 103 Early Human Origins:  ANT 103 Early Human Origins Misconceptions of Human Origins:  Misconceptions of Human Origins Misconceptions:  Misconceptions These stories are far from factual, yet they offer us some interesting understandings of our misconceptions regarding primates and early human origins. Changing Timelines and Challenging Theories:  Changing Timelines and Challenging Theories Previously we have discussed the topic of paradigm shift and normal science as it relates to the updating and challenging of scientific understandings of our world. This same process applies to our understandings of early human origins. Changing Timelines and Challenging Theories:  Changing Timelines and Challenging Theories An interesting exercise is to compare the taxonomy of early humans. Even our own textbook is out of date in regards to charting our origins on a timeline. Changing Timelines and Challenging Theories:  Changing Timelines and Challenging Theories Here are two examples of contemporary early human origins timelines. Changing Timelines and Challenging Theories:  Changing Timelines and Challenging Theories Here are two examples of contemporary early human origins timelines. Evolutionary Misconceptions:  Evolutionary Misconceptions Bigger is Better Newer is Better Natural Selection Always Works There is Always an Inevitable Direction in Evolution (example of orthogenesis) Natural Selection Always Produces Perfect Structures All Structures Are Adaptive Current Structures Always Reflect Initial Adaptations Who Are We, Then?:  Who Are We, Then? I have provided you a detailed handout on early humans, but we can briefly review some of the major archaeological finds and their early human counterparts. Who Are We, Then?:  Who Are We, Then? Recent Discoveries:  Recent Discoveries Toumai Sahelanthropus tchadensi:  Toumai Sahelanthropus tchadensi The recent discovery of a fascinating new hominid species in the central African country of Chad rocks the foundation of the human family tree as we know it. The fossil skull found, nicknamed Toumai is as old as any hominid fossil found to date, yet its features appear much more human-like than those of other contenders for title of human ancestor. Kenyanthropus platyops :  Kenyanthropus platyops Meave Leakey announced the discovery of a new genus of fossil hominid that was discovered by her team in August of 1999. Consisting of an nearly complete skull as well as a partial jaw. The morphological features of Kenyanthropus place it into a separate genus than contemporaneous species like A. afarensis. Although the recent discovery of Toumai (Sahelanthropus tchadensis) has suggested that our ancestors diverged from apes to more than 6-7 million years ago, Kenyanthropus is a significant discovery that we will certainly continue to learn more about as new information is published. Ardipithecenes:  Ardipithecenes Ardipithecus ramidus:  Ardipithecus ramidus A mandible and partial postcranial skeleton of a single individual was found in 1994. Analysis and publication on this find has yet to be made. Once completed, this should provide significant insight into the positional repertoire of Ardipithecus ramidus, dispelling all doubt as to whether or not this truly was a bipedal hominid. Ardipithecus ramidus:  Ardipithecus ramidus Ardipithecus ramidus:  Ardipithecus ramidus The single species from this genus, A. ramidus, dates to approximately 4.5 mya.  This earliest hominid has been identified from deposits in the locality of Aramis, Ethiopia.  Most likely, this individual was part of a radiation that included other hominids and/or hominoids.  Because of its recent discovery, age (and thus contentious value), descriptions remain unpublished.  The specimen’s hominid affinities have been verified and we can thus infer morphological adaptations required of bipedalism.  These include a valgus knee angle, anteriorly placed foramen magnum and most importantly, a short, broad pelvis. Australopithecines:  Australopithecines This genus is made up of several species that fall under two general types, robust forms and gracile forms.  Both of these types are known from fossils found in South Africa and East Africa.  The robust forms persist from ~ 4-1 mya while the gracile forms appear ~ 4 mya but disappear ~ 2 mya.  (It has been suggested that the latest australopithecine species gave rise to the earliest members of Homo.)  It is likely that these hominids enjoyed a pan-African dispersal which we are unaware of due to the preservation biases of such great fossil hunting locales as are found in South and East Africa.  The differences in type between the robust and gracile australopithecines is viewed as differences in adaptive profiles.  The cranial and facial morphology of these two types indicates different diets and thus separate niches.  This helps explain the co-evolution of these two groups on the same landscapes for 2 million years. Gracile Australopithecines:  Gracile Australopithecines Gracile Australopithecines:  Gracile Australopithecines The adaptive profile for the gracile australopithecines includes the ‘humanesque’ generalist advantage.  That is to say that rather than specializing in hard-to-process herbivorous food, the graciles’ specialization is in generalism.  The absence of bony crests for heavy chewing muscles, the presence of smaller cheek teeth with an emphasis on the anterior dentition and the generally ‘lighter’ appearance of the gracile species indicate this hominid as having a more opportunistic approach to carving out a niche for one’s self.  These forms appear ~ 4 mya, the same time as their robust counterparts, and persist until ~ 2 mya.  Gracile species include A. anamensis, A. africanus and A. afarensis.  The recent discovery of A. garhi introduces a likely candidate for the origin of Homo.  The discovery of this specimen associated with stone tools has forced the anthropological community to question the formerly held notion that lithic technology did not appear until the origin of Homo. Australopithecus afarensis:  Australopithecus afarensis The species A. afarensis is one of the better known australopithecines, merely with regard to the number of samples attributed to the species. The species was named by D. Johanson and T. White in 1978. This lead to a heated debate over the validity of the species (seen in a 1980 issue of Science), with the species eventually being accepted by most researchers as a new species of australopithecine and a likely candidate for a human ancestor. Possibly the best-known specimen of afarensis is AL 288-1 ("Lucy"), a 3.2 million year old partial skeleton found in November 1974 at Hadar, Ethiopia. The afarensis can be separated into two chronological categories: early (3.9-3.5 myr) and late (3.5-2.96 myr). Early afarensis includes material from Laetoli and Belohdelie (and possibly Sibilot Hill), with later afarensis known mainly from Hadar and Maka. Other important specimens attributed to afarensis include the AL 333 specimens (such as A.L. 333-105), AL 444-2, AL 129-1A + 1B, the Laetoli footprints, and the type specimen for the species A. afarensis, LH 4. Australopithecus africanus:  Australopithecus africanus The species of Australopithecus africanus was named in a February, 1925, issue of Nature by Raymond Dart. Dart was one of the pioneers of paleoanthropology, and created quite a furor over naming the fossil specimen (the Taung Child skull and endocast) a hominid. The standard line at the time by some of the powerful figures in the field (e.g., A. Keith and O. Abel) was that the ancestors of humans should be found in Europe, and should have an enlarged brain and an apelike jaw (as was the case in the Piltdown Man hoax). The claim that the specimen was a hominid was rejected by those who saw the material as that of a young chimpanzee or gorilla. This view was not helped by the difficulty in acquiring casts. The material was distant from many in the field (few of which ever traveled to actually view the material), and most importantly, was that of a juvenile. Juveniles are often misrepresentative of adult states, and most researchers claimed that the Taung Child would have developed into a chimpanzee or gorilla ancestor. Australopithecus anamensis:  Australopithecus anamensis Though not recognized as such for 30 years, the first Australopithecus anamensis discovery occurred in the Kanapoi region of East Lake Turkana in 1965 by a Harvard University expedition. The initial find consisted of a partial left humerus [Johanson and Edgar, 1996]. Aside from a solitary molar discovery in 1982, virtually no further A. anamensis specimens were found until the early 1990's, at which time, Meave Leakey and other affiliates of the National Museums of Kenya organized a research team for the Kanapoi region [Coffing, et al, 1994]. Australopithecus garhi:  Australopithecus garhi The naming of a new species is almost always controversial, and Australopithecus garhi is no exception. Named in the April 23, 1999, issue of Science, the large research group that discovered the finds made some broad claims and supposition that is definitely not accepted by all, though any real acceptance of these claims and/or hypotheses will have to come later on, as time enough passes for the information has been fully disseminated, others have had a chance to examine the remains, and the dust has settled. The remains that are directly attributed to the new species come from the Hatayae Member of the Bouri Formation, Ethiopia, and have been dated to approximately 2.5 myr. The type specimen of the species is BOU-VP-12/130, an associated set of cranial fragments comprising the frontal, parietals, and maxilla with dentition. The specimen was discovered by Y. Haile-Selassie on November 20, 1997, and the word garhi means "surprise" in the local Afar language. These specimens are important no matter what the eventual final attribution, due to the fact that the remains are from East Africa at a time when there is very little remains (2.0-3.0 myr). Robust Australopithicines (Paranthropus):  Robust Australopithicines (Paranthropus) Robust Australopithicines (Paranthropus):  Robust Australopithicines (Paranthropus) The adaptive profile of the robust species indicates reliance on a diet of fibrous, gritty vegetation.  The extremely large cheek teeth, robust mandible and heavy bony architecture (i.e. zygomatic arch) which supports strong chewing muscles serve as convincing evidence for a diet requiring intense mastication.  These forms appear ~ 4 mya and persist until ~ 1 mya.  Throughout their existence, the robust australopithecines are sympatric with the gracile forms and later with early Homo.  Robust species include A. aethiopicus, A. boisei and A. robustus. Australopithecus aethiopicus:  Australopithecus aethiopicus The discovery of KNM-WT 17000 (the "Black Skull") in 1986 proved to be an important part of the australopithecine puzzle. Very little is known about Australopithecus aethiopicus, since so few specimens have been attributed to the species, but the features that are known provide important insights into the possible evolutionary history between the "robust" and "gracile" australopithecines. In general, aethiopicus shows a mixture of both primitive and derived features, and dates to a time that makes it a significant addition into the hominid phylogenetic tree. Australopithecus boisei:  Australopithecus boisei The discovery of the specimen OH 5 ("Zinj") in 1959, by Mary Leakey, was a watershed in the history of paleoanthropology. The find vindicated Louis and Mary Leakey's work at Olduvai (which had been relatively fruitless over the previous 30 years), which led to renewed research interest in the area, added an important stage in a relatively sparse hominid lineage at the time, and also was important in focusing attention on multidisciplinary research. The fairly complete cranium (sans mandible) was given the species name Zinjanthropus boisei by Louis Leakey, which eventually became known as Australopithecus boisei. However, Zinjanthropus lives on in the well known nickname of OH 5, "Zinj". Australopithecus robustus:  Australopithecus robustus The species Australopithecus robustus was first discovered and named by the eminent Dr. Robert Broom. Broom made a habit of buying fossil remains from a lime quarry worker, and on a particular visit on June 8, 1938, Broom bought a maxillary fragment containing a first molar. The shape and the size of the molar convinced Broom that this was a different species than A. africanus (Broom's transvaalensis), and upon further investigation, found that the specimen had been found by a young boy who worked in the cave as a guide on Sundays. Broom searched for the boy (Gert Terblanche) and found him at school. Broom lectured the boy's class on the cave sites of the area, and was then led to the place of the specimen's discovery, Kromdraai. Broom found several more cranial and mandibular fragments associated with the original maxillary specimen, and this partial cranium (TM 1517) became the type specimen for A. robustus. Genus Homo:  Genus Homo Genus Homo:  Genus Homo The emergence of the genus Homo, ~ 2.5 mya, precedes the later H. erectus species which is most likely the first hominid to leave Africa.  The genus Homo includes species such as H. habilis, H. erectus, and H. sapiens (including Neanderthals).  I will posit the view of the regional approach mentioned earlier.  At the time of the dispersal of H. erectus out of Africa ~2 mya, the sapien human lineage was established.  The establishment of separate populations of H. erectus in Eurasia created insular, regional groups that traded genes with neighboring regions.  This model of gene flow argues that the regional variations we see in modern humans (i.e. racial differences), are the products of 2 million years of limited inter-populational gene flow as well as much intra-populational gene flow.  This model can be viewed as several gene pools being established soon after the Out-of-Africa hominid dispersal.  These ever-growing gene pools began to establish ever-growing connecting streams, which maintained enough genetic homogeneity, that a single, inter-breeding species remains.  We, as modern humans, are the products of this pooling model. Homo habilis:  Homo habilis Homo habilis is a well-known, but poorly defined species. The specimen that led to the naming of this species (OH 7) was discovered in 1960, by the Leakey team in Olduvai Gorge, Tanzania. This specimen and its designation was the subject of much controversies up through the 1970s. The material was found in the same region where A. boisei had previously been found, and many researchers of the time did not fully accept that the material was sufficiently different from that material (or maybe A. africanus) to denote a new species. Louis Leakey was convinced that this was the Olduvai toolmaker he had spent his life looking for, and placed this as a direct human ancestor, with H. erectus a dead-end side-branch. Homo rudolfensis :  Homo rudolfensis The species designation of Homo rudolfensis is a much debated topic, over both whether it is a separate species, and if it is an australopithecine rather than a member of the genus Homo. The type specimen of the species is KNM-ER 1470. This specimen was discovered by Richard Leakey's team in 1972, east of Lake Turkana at Koobi Fora in northern Kenya. This discovery was of a fairly complete cranium without any remaining teeth. Due to uncertainties created by its large brain size and its early initial dates, Leakey did not attribute the specimen to a species, but simply as a member of the genus Homo. Homo ergaster :  Homo ergaster Homo ergaster is one of the more problematic of somewhat accepted species designations currently tossed around in anthropological literature. Each individual researcher that sees ergaster as a valid taxon sees different specimens as belonging or not belonging to the taxon. Many researchers deny any validity to the species at all. On the whole though, most researchers see too little difference between ergaster and erectus to form the basis of a species of the former, separated from the latter. As a general rule of thumb, one can consider most attributed ergaster specimens to be early erectus geographically confined to Africa (however, this is not a hard and fast rule). Homo heidelbergensis:  Homo heidelbergensis This specimen has been recorded at localities spanning Africa, Mediterranean Europe and Eastern Europe at times ranging from ~ 600,000 ya – 200,000 ya.  This specimen is unusual for it displays a mosaic of features, which are most similar to H. erectus.  However the non-erectus features and temporal and spatial distribution make this specimen a likely candidate for the progenitor of the Neanderthal stock. Homo antecessor :  Homo antecessor Homo antecessor was named in 1977 from fossils found at the Spanish cave site of Atapuerca, dated to at least 780,000 years ago, making them the oldest confirmed European hominids. The mid-facial area of antecessor seems very modern, but other parts of the skull such as the teeth, forehead and browridges are much more primitive. Many scientists are doubtful about the validity of antecessor, partly because its definition is based on a juvenile specimen, and feel it may belong to another species. (Bermudez de Castro et al. 1997; Kunzig 1997, Carbonell et al. 1995) Homo antecessor :  Homo antecessor Homo antecessor (Latin: human forbear) possessed characteristics of both neanderthals and Homo sapiens. With the bulky brow and big jaw of the now extinct neanderthal and the cheekbones and nose of Homo sapiens, the researchers believe they have discovered a missing link that may cause a major reconsideration of human ancestry. "This combination of characteristics is unique. It doesn't appear in any other hominid," said Antonio Rosas, a co-author of the study published in Science. "From a logical viewpoint, it fits into an easily definable space, the common ancestor of Homo sapiens and  Neanderthals." Homo erectus :  Throughout the early years of paleoanthropology, there were only two different species that were attributed to the genus Homo. These included the Neanderthals, and Homo erectus. In the early 1960s, this began to change, and human ancestry seemed to be populated by many different players. Accordingly, erectus is one of the better-known members of genus Homo, especially in terms of its well-established place in paleoanthropology. This has begun to change, however, and now some question its place in human evolution. Homo erectus Homo neanderthalensis :  The beginning of paleoanthropology as a scientific discipline began on an August day in 1856. On that day the specimen that was to become known as Neanderthal 1 was discovered in the Feldhofer grotto, in the Neander Valley, Germany. The material was found in a limestone quarry near the city of Düsseldorf. The material recovered consisted of a skull cap, two femora, the three right arm bones, two of the left arm bones, part of the left ilium, and fragments of a scapula and ribs. These fossils were recovered by the quarry workers and set aside to be given to a local teacher and amateur naturalist, Johann Karl Fuhlrott. Fuhlrott suspected that these bones represented unique pieces of the human past, and left the description of the material to anatomist Hermann Schaaffhausen. The find was announced jointly in 1857, two years before Darwin's On the Origin of Species. Homo neanderthalensis Homo sapiens :  The discussion of our species, Homo sapiens, is probably the most difficult to put together. Whereas in the previous species have been introduced with historical background and a discussion of the early, most important finds, and the individuals responsible for the species designation, this introduction will focus on some of the theory implicit in the discussion of the origin and spread of H. sapiens. Homo sapiens Points of Comparison :  Points of Comparison To be continued… :  To be continued…

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