Adaptation and Bipedalism in Early Hominins

Adaptation

A trait that increases an organism's fitness in a given environment.

Adaptationism

The perspective that most traits are evolutionary adaptations.

Ardipithecus

Early hominin genus (e.g., Ardipithecus ramidus), showing facultative bipedalism.

Great Rift Valley

East African geological feature rich in hominin fossils.

Holism

many apparent adaptations may be a by-product of the natural selection process; must take entire organism into account to evaluate which features are adaptive/actually beneficial (fox experiment-ears and tail differences based on aggressive or docile→ every part related and by products of successful traits)- opp of adaptationism

Hominin

Humans and extinct bipedal ancestors (post-split from chimpanzees).

Oldowan tools

Earliest stone tools (~2.6 mya), associated with H. habilis.

Orrorin tugenensis

~6 mya hominin with possible bipedalism (Kenya).

Pelvis

Key bipedal adaptation: shorter, broader, and bowl-shaped.

Reductionism

Explaining complex phenomena by breaking them into parts.

Robusticity

How strong and projecting our skulls are - fluctuates throughout human history

Sahelanthropus tchadensis

~7 mya hominin (Chad), possibly bipedal.

Tool industry

A tradition of toolmaking (e.g., Oldowan, Acheulean).

Valgus angle

Knee angle aligning femur toward center of gravity (bipedalism).

Foramen magnum

Anatomical change for bipedalism located forward.

S-shaped spine

Anatomical change for bipedalism usually C-shaped

Shorter broader pelvis

Anatomical change for bipedalism.

Valgus knee

Anatomical change for bipedalism.

Arched foot

Anatomical change for bipedalism.

Non-opposable big toe

Anatomical change for bipedalism.

Turnover Pulse Hypothesis:

during periods of climate change, generalists (can fill multiple niches) do better than specialists (only 1 niche), can move across land and utilize new resources→ great diversification and speciation; Pros= extreme interglacial/glacial periods, many turnover events, ultimate survivor (homo) was a generalist; cons: doesn't account for particular traits, little evidence affected hominins

Forest Hypothesis

contradicts Savannah; hominins developed in forested environmentals and bipedalism began as an arboreal form; Pros= pollen evidence supports closed habitats, earliest bipedal fossils come from these, bipedal but opposable hallux, no evidence of knuckle walking in LCA; Cons= fossilization better in wet environments so may have disproportionate sample, evidence for knuckle walking hard to prove

Variability Selection Hypothesis

development of hominins slower than the pace of climate changes, traits that allow survival through extreme changes in climate; Pros= similar to turnover but adapted to hominins, pace of hominin evolution slower than climate change; Cons: evidence of pace of hominin evolution based on lumping and limited fossil record

Pulsed Variability Selection Hypothesis

changes in deep lakes of Great Rift Valley→ allopatric speciation but species eventually come back together= huge amount of diversity; Pros: evidence of massive lake changes, explanation for diversity; Cons: variability does not define expected traits; degree of variability and lakes as drivers of speciation still debated

Savannah/Aridity Hypothesis

expansion of savannah and aridity of environment→ increased faunal diversification→arboreal ancestors had to become bipeds; Pros= worldwide increased aridity b/w 8-6 mya; Con: bipedal fossils mostly in wet, closed environments meaning clearly arboreal→ mostly debunked hypothesis

Australopithecus species

Gracile (e.g., Au. afarensis) vs. robust (Paranthropus).

Lucy

Famous Au. afarensis skeleton (~3.2 mya, Ethiopia).

Paranthropus

Robust australopithecines (large molars, sagittal crest).

Prognathism

Projecting jaws (reduced in Homo).

Taung child

Au. africanus fossil, first evidence of bipedalism in Africa.

Australopithecine ancestor-descendant relationships

Au. anamensis → Au. afarensis → Au. africanus → Homo? Debate over whether Au. sediba or Au. garhi led to Homo.

Robust forms

Paranthropus are likely dead-end lineages.

Acheulean tools

Bifacial handaxes (H. erectus).

Levallois technique

Prepared-core toolmaking (Neanderthals).

H. erectus/ergaster

First to leave Africa (~1.8 mya), reached Java/China.

Neanderthals

Cold-adapted, Mousterian tools, burial rituals.

Denisovans

Asian sister group to Neanderthals, known from DNA/finger bone.

Defining Homo

Larger brains (>600cc), reduced dentition, tool dependence.

Scavenging vs. hunting

Confrontational: stealing kills; passive: scavenging leftovers.

First out of Africa

H. erectus (~1.8 mya), dispersed to Eurasia (Dmanisi, Java).

Neanderthal behavior

Intentional burial, symbolic artifacts (e.g., pigments).

AMH features

High forehead, chin, reduced brow ridges, globular skull.

Bering Land Bridge

Route for peopling the Americas (~16kya).

Clovis culture

Early American tool tradition (~13kya).

White Sands footprints

~23kya evidence of humans in Americas.

Encephalization Quotient (EQ)

Brain size relative to body size; correlates with cognitive complexity.

Language characteristics

Symbolism, displacement, productivity, grammar.

Cave art effort

Complex pigment mixing (e.g., ochre) and scaffolding use.

Prominent subsistence

Foraging (95% of human history).

Americas evidence

Reliable: White Sands footprints, Monte Verde (~14kya). Less reliable: controversial pre-Clovis sites.

Pottery significance

Marks sedentism (Neolithic), as it's fragile for mobile foragers.

Agriculture vs. horticulture

Agriculture is large-scale, surplus-producing; horticulture is small-scale.

Göbeklitepe without domestication

Ritual gathering site preceding agriculture (social complexity first).

Climate and urbanization

Holocene warming (~10kya) enabled stable food production.

Göbeklitepe's meaning

Stelae suggest communal rituals; no houses, but labor organization.

Çatalhöyük

~9kya, ~8,000 people, early urban center with domesticated wheat/sheep.

mesolithic

The Mesolithic period, also known as the Middle Stone Age, is a transitional period between the Paleolithic (Old Stone Age) and the Neolithic (New Stone Age), characterized by a shift from purely hunter-gatherer lifestyles to the beginnings of settled communities and agriculture

megalithic

large, prehistoric stone monuments constructed by ancient societies. These monumental architectural works are characterized by the use of massive stone blocks, often weighing several tons, that were carefully selected, transported, and assembled without the aid of modern machinery.

Mousterian tools

an archaeological industry of stone tools, associated primarily with the Neanderthals in Europe, and to the earliest anatomically modern humans in North Africa and West Asia.

Aurignacian Tool Industry

Upper Paleolithic in Europe, is characterized by the production of fine blade tools and bladelets from prepared cores, along with worked bone and antler, and is associated with early cave art and other cultural innovations.

brochas area

Controls language expression - an area of the frontal lobe, usually in the left hemisphere, that directs the muscle movements involved in speech.

Coxcatlan Cave

high dry cave well preserved of the Archaic period show transition of domestication in mesoamerica (Teosinte)

Azilian and Tardenosian

cultures, both part of the Mesolithic period in Europe, are characterized by the use of microliths (small stone tools) and represent a transition from the Paleolithic to the Neolithic periods, with the Azilian in the south and the Tardenoisian in the north.

Backed Blade

Stone blade tool in which one edge has been dulled or "backed" so it can be more readily held in the hand while being used

Burin

A pointed tool used for engraving or incising.

Celts

Peoples sharing a common language and culture that originated in Central Europe in the first half of the first millennium B.C.E.. After 500 B.C.E. they spread as far as Anatolia in the east, Spain and the British Isles in the west. Conquered by Romans and displaced by Germans and other groups, today they are found in some corners of the British Isles.

Corded Ware Pottery

a type of earthenware pottery characterized by cord-like impressions or ornamentation, typically found in Central and Northern Europe during the late Neolithic and early Bronze Age.

Doggerland

land / ice bridge that connected mainland Europe to the British Isles during the late prehistoric period

Cattle cult

people buried cattle showing belief in higher powers

Replacement Model

The hypothesis that only one subpopulation of Homo erectus, probably located in Africa, underwent a rapid spurt of evolution to produce Homo sapiens 200,000-100,000 years ago. After that time, H. sapiens would itself have multiplied and moved out of Africa, gradually populating the globe and eventually replacing any remaining populations of H. erectus or their descendants.

Australopithecus aethiopicus

Lived: ~2.7-2.3 million years ago

Region: East Africa (especially Ethiopia and Kenya)

Notable Traits: Strong jaw and massive chewing muscles; known for the "Black Skull" fossil. Considered a robust australopith.

Australopithecus afarensis

Lived: ~3.9-2.9 million years ago

Region: East Africa (Ethiopia, Tanzania)

Notable Traits: Famous for the "Lucy" fossil; walked upright but retained some tree-climbing adaptations. A key ancestor in human evolution.

Australopithecus africanus

Lived: ~3.3-2.1 million years ago

Region: South Africa

Notable Traits: First Australopithecus species discovered (Taung Child); more rounded skull and smaller teeth than afarensis.

Australopithecus anamensis

Lived: ~4.2-3.9 million years ago

Region: East Africa (Kenya and Ethiopia)

Notable Traits: Oldest known Australopithecus species; walked upright; has a mix of ape-like and human-like traits.

Australopithecus bahrelghazali

Lived: ~3.5-3.0 million years ago

Region: Central Africa (Chad)

Notable Traits: Known from a single jawbone; its classification is debated, but it shows that Australopithecus was more widespread than previously thought.

Australopithecus boisei (sometimes classified as Paranthropus boisei)

Lived: ~2.3-1.2 million years ago

Region: East Africa

Notable Traits: Known as "Nutcracker Man" due to huge jaws and teeth; specialized in tough, fibrous diets. Considered robust.

Australopithecus garhi

Lived: ~2.5 million years ago

Region: Ethiopia

Notable Traits: May have used tools; shows a mix of primitive and derived traits; possibly a direct ancestor of early Homo species.

Australopithecus robustus (sometimes classified as Paranthropus robustus)

Lived: ~2.0-1.5 million years ago

Region: South Africa

Notable Traits: Another robust species; large chewing muscles and flat face; lived alongside early humans but was not a direct ancestor.

Australopithecus sediba

Lived: ~1.98 million years ago

Region: South Africa

Notable Traits: Shares traits with both Australopithecus and Homo; possible transitional species; very important in evolutionary studies.

Homo erectus

Lived: ~1.9 million - 110,000 years ago

Region: Africa, Asia, and parts of Europe

Notable Traits: First hominin to leave Africa; used fire and tools; had a larger brain and more modern body proportions.

Homo ergaster

Lived: ~1.9 - 1.4 million years ago

Region: Africa

Notable Traits: Sometimes considered an African form of H. erectus; slightly more primitive; possibly the first Homo species to show modern body proportions.

Homo floresiensis

Lived: ~100,000 - 50,000 years ago

Region: Flores Island, Indonesia

Notable Traits: Nicknamed "Hobbit" for its small size (~3.5 ft tall); tiny brain but used tools; probably a dwarfed descendant of H. erectus.

Homo habilis

Lived: ~2.4 - 1.4 million years ago

Region: East and Southern Africa

Notable Traits: "Handy man"; one of the first tool users; brain size larger than Australopithecus but still primitive in many features.

Homo naledi

Lived: ~335,000 - 236,000 years ago

Region: South Africa

Notable Traits: Small brain but surprisingly advanced behavior (burial-like practices); very recent discovery; unique mix of ancient and modern traits.

Homo neanderthalensis

Lived: ~400,000 - 40,000 years ago

Region: Europe and western Asia

Notable Traits: Stocky and strong, adapted to cold climates; used tools, buried their dead, and had complex social behavior; interbred with modern humans.

Homo rhodesiensis

Lived: ~300,000 - 125,000 years ago

Region: Africa (Zambia)

Notable Traits: Sometimes considered an African precursor to H. sapiens or H. heidelbergensis; large brain and robust skull; taxonomy is debated.

Homo rudolfensis

Lived: ~2.4 - 1.8 million years ago

Region: East Africa (Kenya)

Notable Traits: Similar to H. habilis, but with a larger brain and flatter face; some argue it's a distinct species, others say it's part of H. habilis.

Homo sapiens

Lived: ~300,000 years ago - present

Region: Originated in Africa, now global

Notable Traits: Modern humans; known for symbolic thought, language, advanced tools, and culture; only surviving Homo species.

Irhoud 10 Fossil

Confirms that early Homo sapiens existed across Africa much earlier than previously thought

Shows a mix of modern and primitive traits—modern face shape, but elongated braincase

Helps push back the estimated emergence of Homo sapiens by over 100,000 years

Gould and Lewontin

Not every feature has a reason (Spandrels/ byproduct of some adaptations that doesn't have a reason for appearing)

◦Nuchal plane

Direction of neck muscles in relation to head

Midfacial prognathism

forward projection of the middle portion of the face, specifically the maxilla (upper jaw) and nasal region, beyond the plane of the cranium (skull)

Movius line

The line that marked the boundary of the eastern and western cultural complexes during the early prehistoric times

wallace line

an imaginary boundary that separates the distinct fauna (animal life) of Southeast Asia and Australia

Jeulmon Period

period of hunting, gathering, and small-scale cultivation of plants. Archaeologists sometimes refer to this life-style pattern as "broad-spectrum hunting and gathering". Map of archaeological sites in the southern Korea peninsular during the Jeulmun Period.

Jōmon

he Jōmon period is the time between c. 14,000 and 300 BC, during which Japan was inhabited by the Jōmon people, a diverse hunter-gatherer and early agriculturalist population united by a common culture, which reached a considerable degree of sedentism and cultural complexity.

Paleoindian

the earliest inhabitants of North America

haft

a process by which an artifact, often made of bone, stone, or metal is attached to a haft (handle or strap)

k-selected

organisms that exhibit traits associated with stable environments, where competition for resources is high, and survival depends on quality over quantity of offspring, often characterized by slower reproduction, larger offspring, and longer lifespans

lumpers

Scientists preferring to lump new fossils into preexisting categories

-Perspective is that range of variation within species is large

-View evolutionary change as taking place within lineages (anagenesis)