Human Evolution Final Study Guide PDF

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Comprehensive notes on the lectures and readings from Introduction to Human Evolution taught by Professor David Strait. Serves as a study guide for the final exam....

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Key Fossils ● Engis 2 ○ Discovered 1829 at Engis cave in Belgium ○ First human fossil discovered ○ Oddly-shaped → long ○ Neanderthal baby ● Gibraltar 1 ○ Discovered 1848 at Forbes Quarry ○ Neanderthal skull ○ Discovery predates that of the neanderthal type specimen ● Feldhofer 1 ○ Discovered in 1856 in the Neander valley ○ Homo neanderthalensis ○ Long, low cranium and receding brow ● Trinil 2 ○ Discovered in 1891 at the Solo River in Java ○ Eugene Dubois wanted to test the idea that orangutans were the closest relatives of humans ○ Homo erectus but originally thought to be Pithecanthropus erectus by Dubois ○ Long, with a flat forehead and distinct brow ridges ● Eoanthropus dawsoni ○ Discovered at Piltdown in 1912 in England by Charles Dawson ○ Widely accepted as evidence of evolution’s missing link (false) ○ Large brain, ape-like jaw ● Taung ○ Discovered in 1924 at the Buxton Quarry by Raymond Dart ○ Juvenile - 3 years old when died ○ Not an ape or monkey ○ Well-preserved fossilized imprint of neurocranial cavity ○ Swelling on bottom is the cerebellum and we can thus infer that the spinal cord must have exited the skull through the cranium ○ Must have been bipedal and therefore human ○ Small canine and non-projecting face is humanlike ○ Small brain is chimp-size and not humanlike ○ Australopithecus africanus ● KNM-ER 1470 ○ Homo habilis discovered in 1972 at Koobi Fora, Kenya ● Australopithecus afarensis ○ Key discovery in 1973 at Hadar, Ethiopia

○ Partial skeleton (Lucy) ○ Small-brained hominin with big teeth but bipedal ■ Confirmed that bipedalism evolved first

History of Human Evolution ● 1809: Lamarck articulates his first fully formed hypothesis of human evolution ● 1858: Charles Darwin and Alfred Russel Wallace write their paper on evolution ● Thomas H. Huxley: fierce advocate for Darwin ○ Creates structure for modern biology department ○ Gives talks ○ One of which is an analysis of Feldhofer 1 in which he concludes that it is not “the missing link” evolutionarily ● Robert Broom: senior paleontologist from South Africa, studied reptilian ancestors of mammals ○ Discovers other South African Australopithecines that establish there are other early humans besides the Piltdown skull ○ Piltdown skull discovered to be a forgery ● The Descent of Man: 1871 book by Charles Darwin in which he hypothesized that bipedalism was related to tool use in terms of evolution because it freed hands to use tools ○ Essentially, once humans started using tools, the evolution of the precision grip, larger brain, and evolution of language evolved too ○ This hypothesis is wrong, however, because if it were true you would expect these adaptations to all evolve at the same time and they did not ■ The earliest hominins pre-date the earliest tools by 4.5 million years

Context of Human Evolution ● Relative increase of cercopithecoids and decline of hominoids in the Miocene ● Naturally occurring climatic changes were external pressures for selection ○ Tectonic events are a source of climate change ● During the Cretaceous period, North America and Europe were close ● The connection between the Arctic and Pacific Oceans has been closing over the last 15 million years ● Water in the Arctic ocean gets trapped there and an overall cooling trend is related to this ● The world also gets drier

● A cooling trend in the Plio-Pleistocene coincides with increased climatic variability ○ The overall cooling temperature drops the overall temperature down to a threshold which creates cascading effects ● A key tectonic event was the raising of Central America ● Periodic advance and retreat of the glaciers ● Oxygen isotope stages ○ Odd numbered stages are warm ○ Even numbered stages are cold ○ Stage 2 is the last glacial maximum ○ Stage 5 is the last interglacial maximum ● Vegetation also changes over tens of thousands of years ○ Periodic expansion/reduction of vegetation is a serious selection pressure but usually mainly reduction ○ Megafauna used to exist in Europe

What Makes Us Human? ● Large brain ○ Slight increase 3 million years ago ○ 2 million years ago is when it takes off ● Tool use ○ 2.6 million years ago/3.5 million years ago ● Precision grip ○ 2 million years ago ○ Long thumb ○ Broad apical tuffs ○ Flexor pollicis longus ● Language ○ Very complicated trait ○ Evidence doesn’t preserve well ○ Younger than 2 million years ago ● Bipedalism ○ Earliest evidence 7 million years ago ○ No question that it evolved first → defines humans ○ Initially evolved and set us apart from other apes ● Functional morphology of bipedalism ○ Valgus knee joint ■ Knee joint closer together than hip joint ■ Shaft and plane have acute angle between them ○ Hip musculature

■ In gorillas, the ilium is oriented so that the flat part faces forward ■ In humans, the pelvis is bowl-shaped and the ilium faces to the side ■ The lesser gluteal muscles (gluteus medius, gluteus minimus) pass behind the hip joint in gorillas, so their thigh extends when they contract their muscles ■ In humans, because the ilium is rotated, the muscles pass in front of the hip joint so an abduction motion is made when contracting ■ Crucial to bipedalism ○ Large, adducted hallux ■ Your big toe is in line with other toes ■ 80% of your weight is put on your big toe when you walk so it needs to be stable and not mobile as well as large ● Hypotheses of evolution ○ Charles Darwin’s about bipedalism/tool use (see The Descent of Man term up above) ○ Carrying ■ Difficult to test ■ Multitasking, evolution of monogamy, sexual monorphism are related to carrying (load-carrying, child carrying) ○ Thermoregulation ■ We have the ability to sweat to maintain body temperature and bipedalism allows more of the body to be exposed to wind

■ ■ False because no early hominins were found in shady habitats so no need for thermoregulation ○ Feeding posture ■ Standing upright is associated with feeding behavior thus feeding posture hypothesis suggests bipedalism evolved for it and THEN ancestors started walking ■ Presumes that hominins ate a lot of fruit that grew on trees ■ This is compatible evidence that is not fully provable ○ Locomotor efficiency

■ Travelling between food trees, a hominin could not run out of energy ■ This hypothesis thus states that bipedalism evolved because it required less energy than quadrupedal knuckle-walking ○ Vertical climbing ■ When forests disappeared and hominins did not climb on trees anymore, they were pre-accustomed to walking bipedally, so they did ■ Testable

Important Excavation Locations ● Zhoukoudian, China ○ Cave system in Beijing ○ Excavated between 1923-1937 ○ Yielded one of the first species of Homo erectus, called Peking Man ● Olduvai Gorge, Tanzania ○ Excavated 1929-present ○ Odd rocks discovered and are thought to be the earliest evidence of stone tools ■ Oldowan tools ○ Lewis & Mary Leakey ○ 1959 - OH5: Zinjanthropus boisei was discovered and thought to be the toolmaker ○ 1964 - OH7: Homo habilis was discovered and known to be the toolmaker ○ First human fossil to be dated using radiometric methods, specifically potassium-argon dating ● Koobi Fora, Kenya ○ Paranthropus boisei ○ Homo habilis ○ Homo erectus ● Turkana Basin, East Africa ○ Provided archaeological evidence of the first stone tools ○ Controversial because only a few tools are in the right sediments ○ Paranthropus boisei ● Dikika, Ethiopia ○ One bone, shaft of bovid limb with small marks ■ Sharp, angular marks characteristic of stone tool cut marks (earliest?) ● Atapuerca, Spain ○ Network of caves ○ Bodies tossed down a hole ○ Found skull ■ Entire middle of face projects forward

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■ Mandible has gap between last molar and ascending ramus, probably no functional purpose ■ Large nose ■ Double arching of brow ridges ■ Differ slightly from Homo heidelbergensis but have shared, derived characteristics with neanderthals Jebel Irhoud, Morocco ○ ~300 kyr ○ Compare with recent modern human, neanderthal → similar cranial shape to neanderthals Skhul, Israel ○ ~120 kyr ○ Odd, large, projecting brow ridge Qafzeh, Israel ○ ~80 kyr ○ People found that look fully modern, but record is not great Arene Candide, Italy ○ ~28 kyr ○ Hat made of perforated shells

Human Evolution - Major Hominin Groups

Name

Key Species

Age

Region

Size

Activity Pattern

Locomotio n

Diet

Social Organi zation

Key facts

Preaustralopith

Sahelanthropus tchadensis, Ardipithecus ramidus

MiocenePliocene (~7-4.2 mya)

East Africa, NorthCentral Africa

Large (30-60 kg)

Diurnal

“Facultative” terrestrial bipedalism? (able to move on two legs even though they didn’t have many of the adaptations of bipedalism) Arboreal “climbing”?

Frugivore with leaves

?

Earliest known hominins Lived in wooded or savannah-woodland mosaic habitats Small brain (370-400 cc), like apes Small molars + premolars, thin enamel, like apes Somewhat reduced facial projection, foramen magnum (hole on bottom of skull) facing inferiorly (sign of bipedalism), and canine slightly smaller/less projecting → all synapomorphies with

other hominins “Gracile” australopiths

Australopithecu s afarensis, Australopithecu s africanus

Pliocene → early Pleistocen e (4.2-2.0 myr)

Eastern Africa, Southern, NorthCentral Africa

Large (30-60 kg)

Diurnal

Terrestrial bipedalism, some arboreal suspension/c limbing

Frugivory with leaves or nuts/seeds, possibly supplement ed with meat or tubers. Diet probably included mechanicall y resistant (hard or tough) foods

Polygyny ?

Australopithecus africanus first australopith species discovered Lived in wooded/savannah-woo dland mosaic habitats Brain slightly larger than apes synapomorphy with later hominins Large molars and premolars with blunt cusps and thick enamel, thick jaws, further reduced canines Many traits indicating terrestrial bipedalism (synapomorphies with later hominins), although unlike bipedalism in modern humans Possibly used stone tools Several traits indicating arboreal behaviors Considerable sexual dimorphism in body size, although modest dimorphism in canine size

Robust Australopiths

Paranthropus boisei, Paranthropus robustus

Latest Pliocene Early Pleistocen e - 2.7 1.4 myr

Eastern, Southern Africa

Large (30-60 kg)

Diurnal

Terrestrial bipedalism? Other? → bad evidence of terrestrial bipedalism

Uncertain nuts/seeds and tubers are possibilities but can’t rule out fruits and leaves Diet def. Included mechanicall y resistant foods

Polygyny

Lived in more open grassy habitats, some wet and some dry Sagittal crest, inflated zygomatics = massive chewing muscles Brain slightly larger than apes (400-550cc) Massive, thick mandible, massive molars and premolars, hyper-thick tooth enamel, indicating hard foods? Very small canines and incisors (synapomorphy with later hominins) High sexual dimorphism in body size, but not in canine size Descended from gracile australopiths

Early Homo

Homo habilis

Latest

Eastern,

Large

Diurnal

Terrestrial

Possibly an

?

Lived in mosaic habitats

Pliocene → Early Pleistocen e (2.8-1.4 myr)

Southern Africa

(30-50? kg)

bipedalism and some arboreal climbing/sus pension

omnivore, probably some meat

as environments became cooler and drier Brain size larger than gracile australopiths (510-750cc); smaller molars, premolars and mandibles than australopiths although much larger than ours; less projecting face than australopiths; precision grip thus presumed tool maker → all these are synapomorphies with later Homo Possibly more than one species Long upper limb → potentially arboreal? Presumed ancestor of later Homo, likely descended from gracile australopiths Earliest Homo found at Ledi-Guraru, which used to be a mosaic → specimen LD 350-1

Archaic Homo

Homo erectus, Homo heidelbergensis, Homo neanderthalensi s Other species: Homo naledi, Homo floresiensis

Pleistocen e (1.9 myr-40 kyr)

Africa, Asia, Europe

Large (~45-~75 kg)

Diurnal

Terrestrial bipedalism

Omnivore including meat

?? May include monoga my

Recognizably human Large brain (650-1700cc) increases over time; larger body size; robust but otherwise nearly modern postcranial skeleton; reduced molars, premolars, mandibles with less projecting faces → all synapomorphies with modern humans Later populations show reduced sexual dimorphism Increasingly sophisticated stone tools Later populations have controlled use of fire Ecologically flexible; first hominins to leave Africa Later populations buried or systematically disposed of their dead

Modern Homo

Homo sapiens

Middle Pleistocen

Initially Africa,

Large (~45-~13

Diurnal

Terrestrial bipedalism

Omnivore including

Most often

Large brain (1,200-1,600 cc)

e → now (~300 kyr - today)

then global

0 kg)

meat

monoga mous

Tall, rounded cranium, widest superiorly Small, flat face, small teeth and jaws, chin Reduced, divided brow ridge Tall, “lanky” body proportions but variation Technologically sophisticated Behaviorally and ecologically flexible, colonizes world Art, symbolism, and modern language

Key Species of Major Hominin Groups

Name

Hominin Group

Age

Discovery site Key specimen Qualities

Sahelanthropus tchadensis

Preaustralopith

Miocene ~7myr

Toros Menalla in Chad, a geological basin in North Central Africa

T M 266, a cranium that was badly fractured but usable

Humanlike qualities such as a reduced facial projection but small brain

Ardipithecus ramidus

Preaustralopith

Pliocene - 4.2 myr

Middle Awash/Aramis site, Ethiopia

“Ardi” - partial skeleton specimen ARA-VP 61500 from Aramis

Diet info present, suspected to be folivorous Small canines, some facial projection (like chimpanzee) Evidence of bipedalism is not strong, uncertain if valgus knee joint is present Abducted big toe means big toe was grasping, which was not a bipedal feature but rather apelike

Australopithecus afarensis

Gracile Australopith

Pliocene 3.9-2.95 myr

Hadar, Ethiopia Laetoli, Tanzania

“Selam” - partial skeleton, juvenile specimen DIK-1-1 from Dikika “Lucy” - partial skeleton specimen AL-288-1 from Hadar

Valgus knee joint present Cranially oriented scapula Long, curved phalanges

Australopithecus africanus

Gracile Australopith

Pliocene - Early Pleistocene - 3-2 myr

Sterkfontein, South Africa

“Little Foot” partial skeleton, Specimen Stw 578 from Sterkfontein

Brain a little larger than chimpanzees

Paranthropus boisei

Robust australopith

Pleistocene 2.3-1.4 myr

Olduvai Gorge, Turkana Basin, Koobi Fora

Paranthropus robustus

Robust australopith

Pleistocene 1.9-1.5 myr

Drimolen, Swartkrans, Kromdraai

Homo habilis

Early Homo

Latest Pliocene Pleistocene, 2.8-1.4 myr

Olduvai Gorge, Koobi Fora

Homo erectus

Archaic Homo

Early-middle Pleistocene: 1.9 myr-200 kyr

Trinil, Java, Indonesia Zhoukoudian, China Koobi Fora Dmanisi, Georgia

KNM-WT 15000 - youth fossil, almost a modern skeleton, has characteristics of bipedalism which is the first time we can definitively say this

Reasonably fast spread around the globe Acheulian tools used Evidence of advanced social behavior → an individual was found with lost teeth and a bone had been fixed, showing the individual lived for long enough with no teeth because they had gotten assistance from members of their group

Homo heidelbergensis

Archaic Homo

Middle Pleistocene 600-200 kyr

Mauer, Germany Petralona, Greece Dali, China Kabwe, Zambia Bodo, Ethiopia

Mauer mandible discovered in 1907 Petralona more vertical forehead than Homo erectus Trinil specimen

Brain size slightly larger than Homo erectus (1150-1250 cc) Overall cranium more rounded Morphology shows up all over the world Europe: 500-300 kya Africa: 600-250 kya Asia: 500-200 kya Homo erectus still lived in Indonesia by the time Homo heidelbergensis had colonized the world

Homo floresiensis

Archaic Homo

Liang Bua, Flores,

LB1 - partial skeleton & skull

Very small →...