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GWU / Sociology / ANTH 1001 / What are the two earliest features that led to the split between human

What are the two earliest features that led to the split between human

What are the two earliest features that led to the split between human

Description

School: George Washington University
Department: Sociology
Course: Introduction to Biological Anthropology
Professor: Alison brooks
Term: Fall 2017
Tags: intro, to, Biological, Anthropology, notes, and Studyguide
Cost: 50
Name: ANTHRO 1011- Final Study Guide
Description: These notes cover chapters 10-14 for the final exam.
Uploaded: 05/03/2018
19 Pages 17 Views 16 Unlocks
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→ Ch.10: Early Hominins


What are the two earliest features that led to the split between humans and other hominoids:?



Human lineage

● Hominids: all humans and apes

● Hominins: homo sapiens and our fossil relatives (after split w chimps)

● Last common ancestor between chimps and humans 6-10 million years ago What Makes a Hominin

● Habitual bipedalism

● Characteristics of the dentition If you want to learn more check out gh 101 uw

● Elaboration of material culture

● Significant increase in brain size

● Long developmental period and long life span

● Mosaic evolution​ = different traits evolve at different points in time


It is formed as layers of bedrock were dissolved and filled with sediment.



Early Changes

● First changes in lineage were habitual bipedalism and teeth

○ Dentition: Humans leave the sharpening canine complex; smaller anterior teeth ■ Leaves U-shaped​ dental arcade → adopts Parabolic​ dental arcade

■ Muscles of Mastication = Temporalis and Masseter

● Main muscles for chewing

● Humans have less → don’t need as much muscular preparation for food

○ Anatomy of Bipedalism

■ Humans have dorsally positioned shoulder blades as well

● from suspensory ancestors


What is paranthropus?



We also discuss several other topics like What is the human genome project?

■ Center of gravity

● Fixed point, through which body weight is transmitted or balanced

● When humans stand, the COG is situated directly in the midline

● Only minimal​ muscle activity is needed to maintain standing posture

■ Foramen magnum position

● Positioned directly underneath the skull in humans

■ Body proportions

● Intermembral index​ = [forelimb/hindlimb] x 100%

● Chimpanizee ~ 110%

● Human ~ 70%

○ Increased stride length

○ Arms are 70% of the length of legs

■ Vertebral Column

● Cervical neck and lumbar (lower back) curvatures to maintain center of

gravity​ over the pelvis

○ Double curved spine

● Larger​ size of the lumbar vertebrae to support body weight

■ Pelvis shape

● Wide, basin shaped pelvis

● Short, broad, curved iliac blades

● Medial rotation of the ilium in humans If you want to learn more check out cu ochem

● Repositioning of the gluteal muscles

● Dramatic reorganization of the pelvis → Improved lateral stability

during the swing phase of bipedal walking If you want to learn more check out What is the characteristic of frequency?

■ Knee

● Valgus angle of the knee

● When humans walk, the foot falls directly below center of gravity

● Femur is oriented at an angle

■ Foot

● Big toe is not opposed to the other four digits, and is enlarged in size

● Enlarged heel (calcaneus)

● Development of arches

■ Adaptive explanations for bipedalism

● Ability to provision for the family in the context of the evolution of

monogamous systems

● Advantage carrying things with arms

● Moving across forested patches with higher energetic efficiency

→ Human Fossil Record

Possible and Probable Hominins

● Sahelanthropus tchadensis​ (7-6 million years ago, Chad)

○ Earliest evidence of bipedalism

○ Described as the oldest possible hominin

○ Reduced snout, only slightly larger brain, smaller canines and no C-P3 honing complex, foramen magnum moved forward so head rests on top Don't forget about the age old question of Proteins attached to carbohydrates.

■ But primitive in other aspects: U-shaped dental arcade, brain size)

● Orrorin tugenensis​ (6 million years ago, Kenya)

○ Without a doubt is a biped

○ Fragmentary cranial and postcranial remains

○ Femoral morphology is indicative of bipedal locomotion

○ Dental morphology is ape-like (large canines)

● Ardipithecus ramidus​ and Ar. kaddaba​ (5.8 to 4.4 million years ago, Ethiopia ) ○ Intermediate canine size, between apes and later hominins

○ From dense forest area, refutes environmental hypothesis for the origin of bipedalism ○ Pelvis - short and broad ilium, evidence for bipedalism? Related to stabilization ○ Mosaic of characters for both bipedality and climbing

○ Primitive feature: retains divergent big toe

○ Lacked other features for suspension/vertical climbing and knuckle walking seen in apes ○ Ardipithecus is really interesting because it has a mix of arboreal/bipedal features​ in a relatively forested context We also discuss several other topics like What is personality?

○ Summary:

■ Combination of primitive and derived traits

■ Evidence of ancestral position for the hominin clade for Ardipithecus discoverers

■ Evidence of the position of A.ramidus as an early ape or an evolutionary side branch for others

When and Where

● At the end of the Miocene period, we see the earliest human ancestors, origin of first hominins ● Predominantly appeared in Africa; the earliest​ hominis ALL occurred in Africa ● East Africa Rift valley system → geological feature that exposes fossil evidence

Two earliest features that led to the split between humans and other hominoids: ● Bipedalism

● Dentition

Part II: Australopiths

The Genus Australopithecus

● Dentition = reduced canine size; larger cheek teeth; thicker enamel

○ Paranthropus chewing adaptation, postcanine megadontia

● Locomotion = definitive adaptations for bipedalism

● Relative brain size = not substantially enlarged compared to apes

● Body size = smaller than modern humans, with more sexual dimorphism

● Raymond Dart’s description: similar to human condition (not accepted for decades b/c of Hiltdown Hoax)

● Since 1924, many fossils of several species of Australopithecus discovered in eastern and southern Africa

Early Species

● Australopithecus anamensis

○ Mostly from Kenya

○ Derived traits:

■ Reduced canines

■ Larger molars, thick enamel

■ Evidence of bipedalism

■ Derived primitive trait: more U-shaped dental arcade

● Australopithecus afarensis

○ East africa (Kenya, Tanzania, Ethiopia)

○ Specimen “Lucy” and her juvenile version “Salom”

○ Relative small brain size relative to face size

■ relative prognathism

○ Sagittal crest

○ Relatively small canine

○ Large cheek teeth, big chewing muscles, thick enamel

■ Probably ate nuts, grains, hard fruit

○ postcranial skeleton

■ More forward placement of the foramen magnum

■ Lumbar curvature

■ Short, broad pelvis, curved ilium

■ Valgus knee

■ Short toes

■ Enlarged heel, arches, non-opposable big toe

○ Arboreal features

■ Suspensory adaptation

■ Relatively long and curved hand bones

■ Long upper limbs compared to short lower limbs

■ Mobile shoulder joints and upwardly-oriented shoulder blade

○ Body size

■ Significant sexual dimorphism, in range of modern gorillas

■ Smaller bodied than modern humans

○ Diverse Habitats

■ A.afarensis lived in environments ranging from more closed woodland to dry open grasslands

■ The ability to walk AND climb trees would have allowed the, to use resources from all of these environments

● Kenya platyops

○ East Africa

○ Distinctive combo of flat lower face and small molars

○ Perhaps A.afarensis (controversial)

● Australopithecus africanus

○ South Africa

○ Beautifully preserved specimen: “Taung Child” with endocranial crest

○ 3.5-2 million years ago

○ Eastern african fossils dated using volcanic ashes (volcanic eruptions in that area) ○ Formation of south african sites

■ Cave sites​ = formed as layers of bedrock were dissolved and filled with sediments

■ No volcanic ash layers in the south = hard to use chronometric dating

○ Similar to the “lucy” species (A. afarensis)

■ Slightly enlarged brain, rounder cranial vault

■ Less prognathism

■ Less developed nuchal cresting

■ Reduced anterior dentition

■ Cheek bones, larger cheek teeth, thick enamel

■ Sexual dimorphism

■ Some evidence suggests they have more arboreal features (longer forearms) than A.afarensis

● Australopithecus garhi

○ East Africa (2.5 ma)

○ Incomplete cranium, complete arm skeleton

○ Different from earlier species:

■ Relatively large brain size

■ Larger anterior teeth, larger premolars

■ Much longer forelimbs and long legs

■ Found adjacent to site that has stone tool assisted animals

● Evidence of tool use for hunting

● Australopithecus sediba

○ South Africa (2 ma)

○ One of the youngest species

○ Similarities with Australopiths

■ Small brain size

■ Molar morphology

■ Small body size

■ Longer upper limbs

○ Similarities with Homo

■ Projecting nose

■ Smaller teeth and chewing muscles

■ Longer legs

■ Hand with precision grip

Major Evolutionary Trends at 2.5 Million years ago

● Significant cooling trend at this time

● Expansion of open grasslands at the expense of closed forests

● Origination of two groups from Australopithecus: Paranthropus​ and Homo ○ Paranthropus

■ Hypermasticatory complex

■ Increase in cheek tooth size

■ Body size similar to Australopithecus

○ Homo

■ Increase in brain size and capacity for tool making

■ Decrease in prognathism, and postcanine tooth size

■ Increase in body size

→ Ch.11: Rise of the Genus ​Homo

What was happening at the same time

● Global cooling trend associated with drier more open habitats in tropical africa ○ Ice ages and interglacial periods

● Paranthropus 

○ Chewing machines

○ Sagittal crest for more muscle room

○ Enlarged cheek teeth with thick molar enamel; frontal dental reduction and crowding ○ 3 Species of paranthropus 

■ Paranthropus ​aethiopicus 

● (East africa 2.7-2.5 ma)

● Well developed sagittal and nuchal crests

● Prognathism, dish-shaped face

● Relatively small brain

● Forward projecting cheekbones (zygomatics)

■ Paranthropus ​boisei 

● East africa, 2.3-1.2 ma

● Forward-projecting cheekbones

● Reduced prognathism (compared to early ancestors)

● Forwardly-placed sagittal crest

● Thick enamel, enlargement of premolars and canines; postcanine

megadonty

● Anterior dental crowding; marked reductions in incisors and canines

■ Paranthropus ​robustus 

● South africa, 2.0-1.5 ma

● Similar ecologically to boisei:​ Tough foods, especially during times of resource scarcity → large chewing muscles, teeth, and thick enamel

● Homo 

○ Early homo fossils have been found at a number of sites in East and South africa ■ Ledi Geraru (Ethiopia 2.8 ma)

○ Homo habilis

■ Found at Olduvai Gorge, Tanzania

■ Found with flaked stone tools (oldowan tools)

■ Slightly larger brain

■ Discovered by Mary and Louis Leakey

■ → first record of hand made stone tools

○ Early homos as a group: OH 24, OH 7, KNM-ER 1813

■ Larger cranial capacity than early ancestors

■ Slight reduction in size of the cheek teeth; more parabolic dental arcade; thinner enamel

■ Reduced prognathism, more gracile cranium

■ BUT, similar in body size to australopiths

■ Associated with stone tools

■ Anatomically, they are more similar to australopithecus

■ But classification as Homo has been supported by their ability to use and make stone tools

■ Now, evidence that other non-Homo species may have used tools

■ H. rudolfensis (2.4-1.6 ma) and H. habilis (2.4-1.4 ma)

● Debate about whether they are the same species

○ Oldowan tool industry

■ (early stone age/ lower paleolithic; 2.6 Ma - 200 Ka)

■ Cores​ = lumps of stone from which pieces are removed

■ Flakes​ = small fragments removed from cores

■ Hammerstones​ = rounded stones used to remove the flakes

■ Bifacial​ = taking flakes off of either side of stone which you would not see in natural stones

■ What were they used for?

● Access the caracasses of animals to obtain meat

● Break bones to obtain marrow

● Secondary uses

○ Plant processing (USOs)

○ Woodworking

● Other early evidence of tool use

○ Swartkrans, south africa (1.8-1.0 ma)

○ Bouri, ethiopia (2.5 ma)

○ Dikika, ethiopia (3.39 ma)

■ Cutmarked bones

○ Lomekwi, Kenya (3.3 ma)

■ Well before​ earliest Homo

○ How human were the first tool makers?

■ Shared with chimps

● Nut cracking

● Stone tool use

● Stone transport (<2km)

● Stone selectivity

● Small game hunting

■ Unique hominin traits

● Stone transport (>10 km)

● Stone tool manufacture

● Using tools to make tools (woodworking)

● Plant processing (USOs)

● Large game acquisition, carcass processing

○ Hominins probably practiced both hunting and scavenging

○ Opportunistic omnivores

→ The Genus Homo: Out of Africa

● Homo erectus and H. ergaster were the first​ species of hominin to leave africa ○ As far as the fossils we found

○ (1.8 Ma- 30 Ka)

○ Most similar to modern humans

● Pleistocene climate oscillation

○ Colder and more variable climate starting at 1.8 ma

○ Interval marked by repeated glacial cycles. Known as the ice age

○ Huge volumes of water in continental ice sheets

○ Exposed land bridges​ connecting continents

● One species or two?

○ Homo ergaster; Africa (1.9-1.0 Ma)

■ Slightly earlier, african variant of homor erectus

○ Homo erectus; Asia (1.8 Ma-ca. 30 Ka)

● Acheulean tool industry

○ 1.6 Ma - 200,000 years ago

○ More sophisticated technology

○ Symmetrical, biface tools

○ Retouching, soft hammer percussion

● Oldowan and Acheulean technologies

○ H.erectus is associated with both stone industries

○ Movius line​: separates H .erectus populations that developed acheulean tools and those that didn't

■ East asian populations may have migrated out of africa before the acheulean industry developed

■ East asian populations may have lost the acheulean industry because they didn’t find suitable materials

○ Tools have very regular proportions, standardized form

○ Proportions hold for africa, near east, europe

○ Requires more complex cognitive abilities

○ Acheulean Intelligence

■ Requires more complex cognitive capabilities than the Oldowan

■ Mental representation of a target image

■ Advanced planning to arrive at that product and ability to modify technique to achieve that goal

○ Handaxe Usage

■ “Swiss army knife”

■ For processing large animal carcasses

● Tip cuts through joints and meat

■ Wood and other plants

■ Cores (as flake dispensers)

■ Not utilitarian purposes?

● Homo erectus may have been the first species to control fire 

○ Cooking

■ Makes food more digestible

■ Less food is needed to get the same amount of nutrients

■ Some toxins can be neutralized

○ Warmth

■ Important in cold and seasonal environments out of Africa

■ May have been crucial to allow migrations to Asia and Europe

○ Cave occupation

■ Allows the use of caves as shelters

○ Predator protection

■ Especially important for large groups

■ Might be predated upon at night

○ Hunting

■ Part of complex hunting, used on spears

○ Social functions

■ May have facilitated the formation of social bonds and forms of communication ● Human-lit fire (compared to natural fires)

○ More intense and longer lasting; spatially localized and discontinuous

○ Persistent hearth

○ The Early Record

■ Small localized, fully oxidized, magnetically altered sediment patches at Koobi Fora (Kenya, 1.65-1.4 ma), and Chesowanja

■ Not much evidence until 800,00 years ago

● GESHER BENOT YA’ AQOV, Israel

○ Charcoal

○ Burned flints

○ Hearts

○ Burned grass seeds, grains (cooking?)

● The enigmatic Homo naledi

○ 335-236 Ka; South Africa

○ Looks very similar to H. erectus

■ Relatively human-like body proportions, brain size, cranial

■ But, it’s so relatively young

■ How can you have it survive until 200,000 years ago?

● After leaving Africa

○ Varied environments, from tropical africa into more seasonal and colder regions in Eurasia and the Far East

● Summary

○ Homo ergaster/ erectus (1.8 Ma)

■ Bigger brain

■ Bigger body

■ More mobile

■ Better hunter

■ Tool and increase in cognitive capabilities allowed early hominins to colonize new environments

■ → real shift in hominin evolution

→Ch.12: Archaic ​Homo sapiens ​and Neanderthals

● The Pleistocene was characterized by globally cooler temperatures and more climate variability between glacial and interglacial periods

● Middle Pleistocene hominins:

○ Brains nearly as big as modern humans

○ Faces and postcrania more ruggedly built than modern humans

○ “Archaics” (ca.800-150,000 yrs ago)

■ Primitive Traits​ (similar to H.erectus)

● Long, low skull; thick cranial bones

● Very large brow ridges

● No canine fossa

● No chin

● Postcranial skeleton more robust than modern humans

■ Derived Traits​ (similar to modern H.sapiens)

● Large cranial capacity

● Higher forehead

● Arched, double brow ridges

● Molar size is decreased

■ Distribution Sites

● 1. Sima del Elefante​ (1.3 Ma)

○ Homo sp.

○ The first Europeans-- Spain

○ Oldowan​ artifacts, hominin remains

● 2. Gran Dolina ​(850-950 ka)

○ Homo antecessor, Spain

○ Oldowan​ tools

○ Cutmarks on human bones

○ Oldest evidence of cannibalism

○ Humans processed in the same way as other fauna

○ Initially described as the last common ancestor​ of Neanderthals

and modern humans

■ Facial traits similar to H.sapiens

■ Dental traits similar to Neanderthals

■ Possibly dead evolutionary end; evolutionary

relationships are not clear

● 3. Sima de los Huesos​ ​(400 ka)

○ Homo heidelbergensis, Spain

○ Clear relationship with Neanderthals

○ “Pit of the bones”:

■ Carnivores and humans; at least 28 individuals

■ Causes of accumulation are not clear (perhaps

intentional)

● Tools

○ Early Stone Age/ Lower Paleolithic 

■ Oldowan​ and Acheulean

○ Middle Stone Age/ Middle Paleolithic 

■ Mousterian​, prepared core technology

■ Middle Pleistocene hominins and Neanderthals

■ Require even more planning than Acheulean tools

■ Bones of large animals associated with Acheulean tools

■ Collaborative hunting effort, complex social patterns

● Middle and Upper Pleistocene: Neanderthals

○ Europe and Western Asia (150-40 ka)

○ Neanderthal

■ Robust, heavily muscled body

■ Barrel-shaped rib cage

■ Thick leg bones

○ Modern human

■ More gracile bodies

○ → Adaptation to different climates and ecological conditions

● H. Neanderthalensis 

○ Systematic use of the mouth as a “third hand”

○ Extremely worn teeth

■ Late Stone Age/ Upper Paleolithic 

● Aurignacian​, blade-based technology

■ Neanderthal subsistence

● Hafted weapons, competent hunting, specialization

● Healthy adults are abundant in the animal remains

● Cut-marked bones, first access

● Also plants included in diet

● No clear evidence of permanent shelters

■ Burials

● Some evidence that Neanderthals buried their dead

● Not clear if these burials had a religious nature

■ They had difficult lives

■ Neanderthal behavioral “modernity”

● Personal ornamentation

● Burials

● Care of elderly individuals

● Rock art

● Neanderthal-modern human interaction 

○ Neanderthals and modern humans co-inhabited in Europe​ for about 10,000 yrs (40-30kya)

■ Both species hybridized​ (demonstrated by DNA analyses)

■ Late Neanderthals associated with Chatelperronian tools, similar to modern human tools

○ Possible relation to their extinction:

■ Direct competition

■ Ecological competition

■ Genetic replacement

○ Denisovans

■ Siberia, 40 kya

■ Little is known about their anatomy; only a finger bone and third molar

■ Based on their DNA sequence:

● Sister group of Neanderthals

● They hybridized​ with modern humans, as Neanderthals did

■ Denisovans and Neanderthals

● Complex relationships between Neanderthals, Denisovans, and modern humans

○ Modern humans vs. Neanderthals

■ Modern humans:

● higher brow

● narrower shoulders

● slightly taller

■ Neanderthals

● heavy eyebrow ridge

● long, low, bigger skull

● Prominent nose with developed nasal chambers for cold-air protection

● Homo floresiensis

○ “Hobbits” → NOT Early Homo nor “Archaic” H. sapiens

○ Comes from the island of Flores in Indonesia

○ No land bridge connected to Flores island to mainland Asia during the Plio-Pleistocene → Need a boat to get there

○ Australopith-like brain size, but more vertical profile to the face

○ About 3.5 ft tall

○ Australopith-like wrists

○ Short lower limbs

○ Flat feet (no longitudinal arch); long curved toes

○ Tool use:

■ Simple flake stone tools (similar Oldowan)

■ Evidence of butchery, hunting

■ Evidence of fire

○ Small size explanation:

■ Insular dwarfism​ ​= reduction in size of large animals when they get isolated in small habitats (islands)

■ In the absence of predators, being small is a selective advantage → less resources are needed

■ Very well known ecological phenomenon observed in many species: dwarf elephants (Stegodon) also in Flores

○ Debated on where they fit on the evolutionary timeline

■ Most likely interpreted as the dwarf lineage of H. erectus

→ Ch.13: Origin of Modern Humans

● First fully modern humans appear in Africa

● H. sapiens =

○ Anatomically modern H. sapiens (AMHS​)

○ Anatomically modern humans

○ Modern humans

● Limited development of brow ridges, small face, small teeth and jaws, no prognathism, large cranial capacity

● First AMHS from Africa

○ Found in Jebel Irhoud, Morocco (300Kya)

○ Then found in Omo, Ethiopia (195 Kya)

○ Herto, Ethiopia (165 Kya)

● Later AMHS

○ Klasies River Mouth, South AFrica (120-90 Kya)

○ Near East in Israel (110-90 Kya)

● AFTER 90,000 ya in the Near East

○ Neanderthals come back when the weather gets colder (70-40 kya)

● Evidence from Archaeology

○ Late Stone Age/ Upper Paleolithic​: blade-based technology made from stone, bone, antler

● Behavioral innovation 

○ Ornaments, more sophisticated tools (net fishing, barbed points), long distance exchange, pigment processing,

○ Behavioral modernity wasn’t associated with abrupt change

○ No single cognitive “explosion”​ that led to the modern human mind

○ Gradual acquisition​ of typically modern human behaviors starting in Africa ○ → There must be more to modern human behavior because we have had anatomically modern people that whole time

● Some especially important innovations by 60,000 years ago in Africa: 

○ Projectile technology

■ More success, less risk, survivorship of hunter increases, competitive advantage ○ Fishing

■ Bone tools, including barbed points → ability to develop new technologies allowed early modern humans to expand their subsistence base; ecological

resource

○ Personal adornment, larger social networks, exchange networks, as evidenced by beads

■ Symbolic behavior that had cultural, ornamental value

■ Social intensification

○ Belief systems​ (burial with grave goods)

■ Ritual burial; suggests concept of life after death

■ Consistency of symbolic behavior

● After 40 Kya; in Europe and Africa

○ Intensification and consistent presence of:

■ Music

● Expression and comprehension of social and emotional info

● Flutes made from animal bones

■ Rock art

● Significance is unclear; magic purpose, to improve hunting success,

ritual

■ Portable art (figurines)

● Expanded Subsistence Base

○ More varied diet, which included use of aquatic resources

● Settlement Patterns

○ Sites occupied for longer periods and extensively modified

○ Evidence of more permanent shelters

Summary:

● Modern Human Advantages

○ Innovative​ = new, more elaborate technologies, projectile weapons, clothing, shelters, and other innovations in material culture

○ Cognitive​ = personal adornment and symbolic behavior, art and music, ritual ○ Social​ = larger social networks, exchange networks, buffered risk of starvation ● Multiregional Model

○ Pleistocene hominins represent a single evolving lineage​ across different regions ○ AMHS evolved in the context of significant gene flow​ between regions

● Out of Africa Model

○ AMHS originated in Africa and later dispersed to occupy the Old World

○ No gene flow

● Assimilation of both models

○ African origin of AMHS

○ Varying degrees of interbreeding with existing populations

○ Best model ​supported by genetic data

■ Greatest amount of genetic diversity in Africa

■ AMHS first appear in the fossil record of Africa

■ Largely replaced populations elsewhere (with some interbreeding)

● Unique modern human behaviors appeared in the record gradually ​over the last 300,000 years

→ Ch.14: Evolution of the human brain and language

Apes

● Sophisticated aspects to their cognitions that are different from other primates: ○ Social learning and “traditions”

○ Tool use

○ Self-awareness and self-recognition

○ Social tolerance

Brains do not fossilize

● Endocranial casts do: general representation of brain size and shape

○ Macro and microscopic comparisons of extant species

Human brains

● Are exceptionally big relative to body size and other primates

● Highly “encephalized” (-Darwin) 

○ Encephalization​ = the proportional size of the brain relative to body size 

● Strong increase in absolute brain size during hominin evolution 

● Humans do not have the largest brains in comparison with extant or fossil species ● Brain anatomy: 

○ Brainstem​ = regulates many basic body functions 

○ Cerebellum​ = integrates sensory perception, coordination and motor control; learning new motor skills 

○ Cerebrum (neocortex)​ = higher cognitive functions, such as sensory perception, generation of motor action/action commands, spatial reasoning, memory, conscious thought, speech, and language 

■ A lot of differences between human brains and others happen in the neocortex ○ Brains are wrinkly to pack more brain tissue into the skull 

● Human brains are highly gyrified: 

○ Gyrification index​ = the degree of folding of the cortex 

■ Ratio of total cortical surface to outer cortical surface 

■ Increases with brain size 

■ Effective brain size can increase without an associated increase of skull 

● Major functional areas: 

○ Frontal lobe​ = many higher cognitive functions associated with intelligence ○ Parietal lobe​ = integrates sensory info from different modalities, important for tool using ○ Temporal lobe​ = primary auditory cortex, visual object recognition, processing of semantics, long-term memory 

○ Occipital lobe​ ​= primary visual cortex 

○ Brain functions are localized​; different areas have different functions 

○ Association cortex = portion of the cortex that does not fall within primary motor and sensory areas 

■ Processing and integrating primary inputs 

○ → Human evolution: large​ increase in association areas 

● Human specialization: cerebral cortex 

○ Cerebral cortex surface is larger than expected for a primate of human brain size ○ Non-uniform expansion of the cerebral cortex 

■ Prefrontal, parietal, and temporal​ areas have undergone the greatest 

expansion 

● Areas associated with language and tool use 

○ Prefrontal cortex involved in decision-making, planning, working memory, and emotional regulation 

■ Expanded in apes in comparison with other primates. Humans show a further expansion of this area compared to apes

○ The human visual cortex is reduced compared to chimpanzees 

■ Related to the expansion of the parietal association cortex, important for tool use ● Characteristics of human language 

○ Voluntary and socially learned 

○ Semantic 

■ Arbitrary symbols (words) convey meaning 

■ Phonemic 

○ Syntax 

■ Language rules (dog bites man vs. man bites dog) 

○ Recursive 

■ Phrases wirthin phrases 

■ Hierarchical structure 

● Language-like abilities of other primates 

○ Evidence of limited mastery of syntax and ability to communicate about things outside their immediate experience; communication able to be learned and containing symbolic info 

● Language processing areas in the brain 

○ Broca’s area​ = speech production 

○ Wernicke’s area​ = speech comprehension 

○ Language area asymmetry = In 95% of modern humans, language function is lateralized to the left hemisphere ​of the brain 

● Anatomy of vocal tract 

○ Human larynx has a lower position compared to chimpanzees 

■ → Allows humans to produce a larger variety of sounds 

○ Human tongue differs in shape and forms the back wall of the oropharynx 

■ → Contributes to producing different sounds 

● FOXP2 = ​Gene involved in speech and language 

○ Almost all modern humans have it; the human one is functionally different​ from other vertebrates 

○ Neanderthals share the derived version of FOXP2 with modern humans 

Evolution of the Human Life Cycle 

● All Primates 

○ Life Stages 

■ Prenatal Period 

● Conception to Birth 

■ Infancy 

● Begins at birth 

● Dependent on mother for nutrition and protection (lactation) 

● Ends with weaning and eruption of first permanent tooth 

■ Juvenile 

● Travel and forage independently 

● Learn important social skills

● Ends with sexual maturation 

■ Adulthood 

● Reproductively mature 

● Begins at eruption of last permanent tooth 

● Distinctive Features of the Human Life Cycle 

○ Childhood 

■ Between Infancy and juvenile period 

■ Occurs after weaning when children are still dependent on others for food ■ Period of learning technical and social skills and languages 

■ Ends with attainment of adult brain size 

○ Adolescence 

■ Between juvenile and adulthood 

■ Begins with the onset of sexual maturity 

■ Allows for an extended period of social learning, and continued brain maturation ■ Marked acceleration of body growth 

■ Ends with attainment of adult height 

● Derived Features of human life history 

○ Long post-reproductive lifespan 

○ Late age at first birth 

○ Long gestation length 

○ Large neotates 

○ Early age at weaning 

○ Short interbirth interval 

● Human babies are bigger and fatter 

○ Accumulation of large fat stores in human infants 

○ Support energetic costs and provide important substrates for brain development ○ Humans devote more energy to brain metabolism​ than other species (60% BMR) ○ Buffers cost of early weaning (human mothers stop producing milk faster) ○ Unlike great apes, humans continue to rely on supplemental nutritional support from others after weaning (provisioning​) 

● Humans have large brains 

○ Humans as ‘secondarily altricial​’ in their brain growth 

○ Human brains are comparatively under-developed at birth 

○ Percentage of adult brain mass at birth: 

■ Humans: 27% 

■ Chimps: 36% 

○ Humans grow a larger proportion of their adult brain size during postnatal life ​(first 18 months) 

○ Hypotheses​: 

■ 1) Obstetrical constraints.​ Bipedalism requires a pelvis with a narrow birth canal 

■ 2) Due to metabolic constraints of gestation. ​Fetal metabolic requirements outpace maternal supply.

■ 3) Selective advantages of extended neural development 

● Key maturational changes in the brain continue through adolescence 

● Brain maturation occurs under massive environments and social 

influences in our species 

● Neural circuits responsible for behavior are shaped by experiences in the 

local environment 

● Unique features of the human body growth curve 

■ Prolonged period of slow body growth during childhood 

■ Marked adolescent growth spurt, which is late in onset and high and magnitude ■ → Human children devote much of their energy into growing large brains ● Slow body growth during human childhood coincides with peak demands 

of brain metabolism 

■ Menopause​ = post-reproductive period in the lives of females, permanent 

cessation of ovulation and menstruation 

● Reproductive termination occurs midway through the lifespan, well 

before advanced somatic aging; slow somatic aging 

● Grandmothering Hypothesis​: 

○ Inclusive fitness ​= benefits derived from older, non-reproductive 

adults who contribute to the care of their grandchildren 

○ By improving the survival success of close relatives, this 

increases the probability of passing down genes 

● Other behavioral correlates: 

○ Early weaning → provisioning 

○ Short interbirth intervals → human mothers may support multiple​ dependent offspring at a time 

○ Extensive paternal care and cooperative breeding​ = reproductive strategy and social system in which non-parental members of a social group help to support offspring who are not their own 

● Dental development as a proxy for life history 

○ Dental histology​ ​= ​daily growth in teeth provide a method of estimating the absolute age of death 

○ → Large skeletal size at M2 eruption suggests that H.erectus​ lacked the modern human pattern of prolonged slow childhood growth 

Important Takeaway: 

● All of these unique human features are relatively recent in the evolutionary timeline 

→ Forensic Anthropology

● Forensic anthropologists apply knowledge of osteology and human variation ● Collaborate with others (medical examiner, pathologists)

● Main jobs:

○ Help in making positive identification

○ Help determine cause of death

■ Forensic genetics can be useful for IDs, but often there are no samples to compare to with unknown victims

■ In very old cases, soft tissue is gone

● Biological profile

○ Age at death

■ Dental eruption sequence offers clues for younger individuals

■ Bone anatomy: patterns of closure are predictable over course of skeletal maturity, within a range of ages

● Epiphyses, pubic symphisis, cranial suture obliteration

○ Sex

■ Pelvis and skull most diagnostic (in adults)

○ Ancestry

■ Tricky to determine, due to overlap between groups, and non-homogeneity of traditional “racial” categories

○ Height and weight

■ Height: relatively straightforward when skeletons are found

■ Weight: fluctuates during lifespan, but related to joint size and width of pelvis ○ Premortem injury and disease

■ Healed fractures can offer clues as to life-experience and identity

■ Specific record of dental procedures in teeth can aid in positive identification ○ Perimortem and postmortem trauma

■ Evidence of non-healed injuries offer important clues as to cause of death Applications of Forensic Anthropology

● Mass fatalities, war crimes, genocide; often work for government and NGO groups

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