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Chapter 13

Chapter 13 How Humans Evolved - Bio 1M03.docx

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McMaster University
James S Quinn

Bio 1M03 How Humans Evolved Part 3: The History Of The Human Lineage Chapter 13: From Hominin to Homo Lumpers and Splitters  Anthropologists disagree strongly about how to classify Middle Pleistocene homins: o Maybe homins in Africa and Eurasia were one, single interbreeding population throughout the Pleistocene o Or maybe homins split into several new species as they migrated out of Africa during the Pleistocene  Differences Exist In The Interpretation of Recent Human Evolution  “Multi-Regional” Hypothesis for Human Evolution  “Complete-Replacement” Hypothesis for Human Evolution Bio 1M03 How do we actually know that climate has changed?  Remember, the concentration of O is higher in the oceans during periods wit cold climates Bio 1M03  The Pleistocene epoch started 1.8 mya and involved a cooling trend that started in the Miocene ~ 6 mya Pleistocene  Lower Pleistocene is from 1,800,00 – 900,000 years ago  Middle Pleistocene is from 900,000 – 130,000 years ago; began with massive glaciation Bio 1M03 o Climate became colder and more variable; cold glacial periods punctuated by short, warner interglacial periods  Upper Pleistocene is from 130,000 – 12,000 years ago and ended with warm interglacial phase  12,000 – present is an interglacial period called the Holocene Hominins of the Lower Pleistocene: Homo ergaster  H. ergaster lived from around 1.8 – 0.6 mya in Africa and Eurasia  May be the same species as H. erectus, which was first found in Indonesia  Ancestral features include narrowing of braincase behind the eyes, receding forehead  Derived feature include shorter nose, less prognathic face, taller skull, smaller jaws and molars, occipital torus (horizontal ridge at back of skull), less sexual dimorphism, large brain  Fully adapted for terrestrial life, lacking adaptations for arboreal life seen in earlier hominins  No evidence that there was a spoken language  More rapid juvenile development than humans, but slower than earlier hominins  H. ergaster was the first hominin to leave Africa  Fossils of this species have been found in the Caucasus Mountains in the Republic of Georgia  The Georgian site of Dmanisi revealed fossils as well as stone tools from this species  H. ergaster has a much larger brain than previous hominins  This species was probably good at tearing and biting with canines and incisors and less good at heavy chewing with molars o Teeth smaller than australopithecines and paranthropines  Brain size o ~800cc, compared to 500-700cc of predecessor hominins o Modern human brains are ~1400cc; chimp brains are ~370 cc Bio 1M03 o Brain size is proportional to body size in mammals – in comparison with earlier hominin species, H. ergaster did not have a substantially larger brain in relation to body size  The discovery of an almost complete H. ergaster skeleton from a 12 year old boy reveals much about body dimensions o Similar to modern humans that live in savannas today – long legs, narrow hips and shoulders, short arms o Tall (adult males probably ~6 ft) o Suggests ability to run long distances – humans can outrun most other species in a long distance race of more than a few km o Morphology of spinal column does not suggest this species had spoken language o Less sexually dimorphic than predecessor hominins o Relatively rapid development – faster than humans but slower than australopithecines o Infants matured slowly relative to hominin predecessors; much brain growth after birth o May not have had a spoken language  Tools o Between 1.6 and 1.4 mya, H. ergaster improved on Oldowan tools and added the stone biface  Biface – a “Mode 2” technological innovation that was part of the Archeulean industry  Toolmaker strikes a large piece of rock from a boulder to make a core, and then flakes this core on all sides to create a flattened for with a sharp edge along its entire circumference  Most common type of biface – hand ax; shaped like a teardrop and have a sharp point at the narrow end o Axes could have been used to  Butcher animals  Dig up tubers or water  Strip bark from trees  As projectiles  To generate flake tools  Cleaver; lozenge shaped biface, with a flat, sharp edge on one end  A Pick; thicker, more triangular biface  This technology overlapped in time with “Mode 1” tools  This type of tool was used for ~1 million years  Designed according to a uniform plan  Homo ergaster was a meat eater o One H. ergaster female had a bone deformity consistent with vitamin A overdose; this can occur if you eat the liver of a carnivore o Fossils of this species is also often found in association with hand axes, animals bones with cut marks from stone tools o Additionally, it survived in temperate regions where fruit yield is seasonal  Probably controlled fire Bio 1M03 o Soil under campfire gets hotter than does soil under grassfires – this causes distinctive changes in soil chemistry and magnetism  Bowl-shaped layer of highly oxidized soil  Soil under the fire becomes highly magnetized o Campfires burn bones in a way that is distinctive from grass fires – bones with campfire burns have been found with H. ergaster remains from numerous strata  H. ergaster considered genus Homo because it shared important adaptive traits with modern humans o Terrestrial life o Complex foraging technology o Slow development o Reduced sexual dimorphism o (probably) extensive paternal investment in offspring Hominins of The Early Middle Pleistocene Origin of Homo erectus  Found in java Indonesia, dating to between 1.8 and 1.6 mya  Persisted in Java and China until about 30, 000 years ago  Morphological differences from H. ergaster o Larger face o Thicker cranial walls o Lower, less domed, steeped cranium o Pronounced occipital torus o Pronounced browridges o Sagittal keel (but no sagittal crest) o Recent fossils of H. erectus from 30,000 years ago are less similar to modern humans than fossils of H. ergaster from 1 million years ago  Tool Use o Associated with Mode 1 tools o Archeulean tools are rarely found in eastern Asia (tools pictured here are an exception) o Lack of Mode 2 tools could be related to different cognitive abilities compared to H. ergaster or to differences in materials available for tool making  Timing of Recent Hominin Fossils o Actual divergence times probably pre-date the oldest fossil! o Time of extinction probably post-dated newest fossil! Homo Heidelbergensis (Archaoic H. sapiens)  Aged between ~800,000 – 500,000 years ago  Fossils evidence comes from areas as diverse as Spain and Zambia  Morphology o Larger brains, between 1,200 and 1,300 cc o Ancestral features included a long, low skull, thick cranial bones, prognathic face and large browridges o Derived cranial features include high foreheads and a more round occipital bone  Tools and Subsistence o Mostly Mode 2 Archeulean tools o Solid evidence for hunting big game Bio 1M03 o These individuals probably also eventually used the Levallois techniques, which is a Mode 3 technology o Levallois Technique Hominins of the Later Pleistocene  Types of Stone Tools o Oldowan/Mode 1 – use a hammer to break flakes off of a core o Archeulean/Mode 2 – involves additional processing of flakes, including working both sides of the flake o Levallois Technique/Mode 3 – modification of shape of core culminating in a final flake cut from a modified core  Some tools were hafted (with handles) Bio 1M03  Climate become colder between 120 and 80 kya 18 16 o Data based on O :O ratios of different layers of cores taken from deep inside the Greenland ice cap  In Ice Caps – higher ratio of O to O indicated higher temperatures  H. Heidelbergensis and H. erectus appeared in eastern Asia  H. Heidelbergensis and H. erectus may have coexisted Neanderthals  Origins o Present in western Eurasia from ~127,000 – 30,000 years ago but probably as far back as 400,000 years ago o Lived in Europe, Eastern Asia and Southern Siberia o Anatomically modern humans were living in these areas at this time from ~80,000 years ago  Morphology o Faces that bulge in the middle o Large brow ridges o Rounded back of skull o Large cranial capacity, around 1400 cc – larger than modern humans o Small back teeth and large front teeth  Taurodont Roots – pulp cavity expanded so that the roots merged, partially or completely, to form a single broad root o Robust, heavily muscled bodies o Language capabilities unknown o Neanderthals were more stocky than modern humans o Morphology may have been an adaptation to conserve heat in a cold environment  Culture o Mode 3 tool industry o Hunted large game o Mostly meat eaters but evidence of plant material has also been recovered on fossil molars o Probably made shelters (book doubts this but other sources support it) Bio 1M03 o Probably wore clothes – evidence of bone sewing needles and awls o Controlled fire also made symbolic or ornamental objects o Deliberate burial of dead and potentially marking of graves with flowers  Suggested by the abundance of complete Neanderthal skeletons  Possibly had a religious nature, or just to rid of decaying bodies o Possibly lacked modern language  “Extinction” o Could potentially be part of the same species as us o Recent molecular data demonstrates that this was a substantially different lineage o Maybe H. sapiens could have been involved with violent conflict and replacement of H. neanderthalensis o Maybe hybridization led to fusion of H. s and H. n o Maybe climate change or energetic requirements made H. n unfit Homo Florensis  Only about 3 feet tall; are the “dwarf people” from Flores Island, Indonesia  Very small brains, around 380 cc – similar to chimps  Lived between 35,000 and 14,000 years ago  Island Flores in Indonesia  Some researchers think these were descendants of H. erectus that became isolated and evolved different characteristics because of natural selection  Alternatively, these individuals made up a modern human population with a small stature and microcephaly  Also possible that this is a lineage that preceded H. erectus into Asia  Comparisons of skulls of modern humans with microcephaly suggested that the H. florensis individuals were not microcephaly  Front and temporal lobes of H. florensis highly developed like normal humans but smaller  Species shorter than the average height of the shortest populations of modern humans  Cave where remains were found had evidence of usage of fire, hunting  Insular Dwarfism o One possibly reason for the small stature of H. florensis is the phenomenon of insular dwarfism o On islands with less predation pressure, species sometimes evolve small stature as a way of existing with lower food intake o Small size could be advantageous for reproduction if gestation and generation duration decreases too  Insular Gigantisms o Sometimes species get larger on islands, not smaller o This could be related species becoming predators on islands because of the absence of other predators (like mammalian carnivores) o Or because decreased predation pressure allows species to be large Bio 1M03  Attempts to extract DNA from H. florensis were unsuccessful; probably due to environmental conditions being bad for long term DNA preservation  Fossils damaged by an Indonesian scientist (Teuku Jacob) Denisova Hominns: A New hominin from Asia  March 2010, scientists reported discovery of a finger bond fragment of a juvenile female of a previously unidentified hominin that lived ~41,000 years ago in a cave in Russia  A tooth and toe bone from this group was found later  This region was probably also inhabited by Neanderthals and AMH (anatomically modern humans) at this time Major Questions in Recent Human Evolution  Recent out of Africa hypothesis vs. multiregional hypothesis Bio 1M03  Did gene flow occur between the African ancestors of anatomically modern humans (AMHs) and other hominins?  Was there population structure in the African ancestor of AMHs?  Did gene flow occur between humans and other lineages outside of Africa (H. erectus or Neanderthals of Denisova)? Multiregional Evolution  Postulates that evolution of modern humans has been occurring since early humans (H. erectus) left Africa 2 mya  Continuous exchange of genes among populations in different regions united this species as It evolved into modern humans  Supported by primitive characteristics in some modern races (eg/ shovel shaped incisors in Asians, prognathic face and large cheeks of Australian aborigines)  But these features could be convergently evolved or simply a polymorphic ancestral feature o Eg/ Ben’s sagittal keel and occipital torus does not prove he is H. erectus Out of Africa/ Complete Replacement Hypothesis  Modern humans dispersed out of Africa and replaced populations of H. erectus and Neanderthals without interbreeding Bio 1M03 Alternative Versions of “Recent out of Africa”  Genetic evidence exists for a single recent ancestry (~100,000 ya) origin of some genes in Africa o Deepest branches of mtDNA and yDNA are in Africa (Cann et al. 1987, Vigilant et al. 1991, Stumpf and Goldstein 2001 and many others) o Linkage disequilibrium studies (Tishkoff et al, 1996) Bio 1M03 o Data from many other genes o Can et al  Mapped restriction enzyme sites in mitochondrial DNA from 147 people from all over the world  Earliest divergence occurred among Africans, non-African mtDNA is derived from an African ancestor Human mtDNA  Variation within African populations is as great as that between Africa and other population sor between other populations  Greatest divergence between non-African haplotypes corresponds to times between 90000 – 180000 years; this implied that early Asian Homo species did not contribute mtDNA that survives in modern humans  Estimates for the age of the mtDNA haplotype is not the “birthdate of the human species”, it is the birth date of that particular mtDNA lineage Intra-species divergence times of some parts of the human genome are very ancient (2 mya)  One way this could happen if there was population structure in Africa before AMG left Africa Bio 1M03  Another way that this could happen if there was gene flow with another diverged hominin  Resear
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