🍖World Prehistory Unit 2 – Early Hominins: Origins and Evolution

Key Concepts and Terminology

• Hominins include humans and our extinct ancestors diverged from the chimpanzee lineage ~7-6 million years ago
• Bipedalism walking upright on two legs a key adaptation that emerged early in hominin evolution
• Encephalization increase in brain size relative to body size over the course of hominin evolution
• Oldowan earliest known stone tool industry associated with early hominins (Homo habilis)
• Acheulean more advanced stone tool industry developed by later hominins (Homo erectus) included hand axes and cleavers
• Australopithecines early hominins that existed between ~4.2-1.2 million years ago had smaller brains and larger teeth compared to later Homo species
  • Gracile australopithecines (Australopithecus afarensis, Australopithecus africanus) had lighter, more slender builds
  • Robust australopithecines (Paranthropus boisei, Paranthropus robustus) had heavier, more robust builds with larger jaws and teeth adapted for tough, fibrous diets
• Homo earliest species of our own genus emerged ~2.8 million years ago characterized by larger brains, smaller teeth, and more advanced tool use compared to australopithecines

Timeline of Early Hominin Evolution

• ~7-6 million years ago (mya) divergence of hominin lineage from chimpanzee lineage
• ~4.4 mya Ardipithecus ramidus one of the earliest known hominins
• ~4.2-3.9 mya Australopithecus anamensis early australopithecine species
• ~3.7-3.0 mya Australopithecus afarensis (Lucy) well-known early australopithecine species
• ~3.3-2.1 mya Australopithecus africanus later gracile australopithecine species
• ~2.8-1.5 mya Homo habilis earliest known species of Homo associated with Oldowan tools
• ~2.3-1.4 mya Paranthropus boisei robust australopithecine species
• ~1.9-0.8 mya Homo erectus first hominin to leave Africa associated with Acheulean tools
• ~1.8-1.2 mya Paranthropus robustus another robust australopithecine species
• ~0.6-0.2 mya Homo heidelbergensis later species of Homo gave rise to Neanderthals and modern humans

Major Hominin Species and Their Characteristics

• Ardipithecus ramidus one of the earliest known hominins had a mix of ape-like and hominin features
  • Bipedal when on the ground but still adapted for climbing trees
  • Small brain size similar to chimpanzees
• Australopithecus afarensis well-known early australopithecine species
  • Fully bipedal but still had long arms and curved fingers for climbing
  • Smaller brain and larger teeth compared to later Homo species
• Paranthropus boisei and Paranthropus robustus robust australopithecine species
  • Large jaws and teeth adapted for tough, fibrous diets
  • Lived alongside early Homo species but went extinct ~1 million years ago
• Homo habilis earliest known species of Homo
  • Larger brain and smaller teeth compared to australopithecines
  • Associated with Oldowan stone tools
• Homo erectus first hominin to leave Africa
  • Taller and more human-like body proportions compared to earlier hominins
  • Associated with more advanced Acheulean stone tools
  • Controlled use of fire

Fossil Evidence and Important Discoveries

• 1924 discovery of Taung Child (Australopithecus africanus) in South Africa first early hominin fossil found in Africa
• 1959 discovery of robust australopithecine fossils (Paranthropus boisei) by Mary Leakey at Olduvai Gorge, Tanzania
• 1974 discovery of Lucy (Australopithecus afarensis) in Ethiopia most complete early hominin skeleton found at the time
  • 40% complete skeleton of a female individual
  • Bipedal but still had curved fingers and long arms for climbing
• 1978 discovery of Laetoli footprints in Tanzania
  • 3.6 million-year-old trail of fossilized footprints
  • Provided clear evidence of bipedalism in early hominins
• 1984 discovery of Turkana Boy (Homo erectus) in Kenya
  • Most complete early Homo erectus skeleton found to date
  • Tall and slender build with long legs adapted for walking and running
• 1994 discovery of Ardipithecus ramidus in Ethiopia
  • 4.4 million-year-old hominin with mix of ape-like and human-like features
  • Helped fill in the gap between earlier apes and later australopithecines
• 2008 discovery of Australopithecus sediba in South Africa
  • Species with mix of primitive and derived features
  • Possible transitional form between australopithecines and early Homo

Environmental Factors and Adaptations

• Climate change and environmental variability major drivers of hominin evolution
  • Shifts between wet and dry periods led to expansion and contraction of forests and grasslands
  • Hominins adapted to changing environments through bipedalism, tool use, and dietary flexibility
• Bipedalism evolved as adaptation to more open, savanna-like environments
  • Walking upright more energy-efficient than quadrupedal locomotion over long distances
  • Freed hands for carrying objects and manipulating tools
• Dietary adaptations
  • Early hominins like australopithecines had large jaws and teeth adapted for tough, fibrous diets
  • Later Homo species had smaller teeth and more diverse diets that included meat and cooked foods
• Encephalization increase in brain size over time
  • May have been driven by social complexity, tool use, and dietary changes
  • Required higher-quality diets to support metabolic demands of larger brains
• Control of fire first evidence ~1 million years ago with Homo erectus
  • Allowed for cooking, which made foods easier to chew and digest
  • Provided warmth, light, and protection from predators

Tools and Technology

• Oldowan earliest known stone tool industry
  • Simple flakes and choppers made by striking one stone with another
  • Used for cutting, chopping, and scraping
  • Associated with Homo habilis and early Homo erectus
• Acheulean more advanced stone tool industry
  • Hand axes and cleavers made by shaping stones on both sides
  • Required greater skill and planning to produce
  • Associated with later Homo erectus and other early Homo species
• Bone and wooden tools also used by early hominins
  • Bone tools used for digging, hide-scraping, and other tasks
  • Wooden spears and digging sticks likely used but rarely preserved in the fossil record
• Control of fire ~1 million years ago
  • Allowed for cooking, hafting of tools, and heat-treatment of stone to improve flaking properties
• Pigments (ochre) used by some early Homo species
  • May have been used for symbolic or aesthetic purposes
  • Hints at the emergence of symbolic thought and culture

Social and Behavioral Developments

• Social organization and group size
  • Early hominins likely lived in small, mobile bands
  • Later species like Homo erectus may have had larger, more complex social groups
• Cooperative behaviors
  • Hunting and scavenging of large animals required cooperation and coordination
  • Sharing of food and resources within groups
  • Care for injured or sick individuals
• Communication and language
  • Increased brain size and complexity over time
  • Anatomical changes to vocal tract and hearing apparatus
  • Symbolic artifacts (pigments, engraved objects) hint at capacity for symbolic thought and communication
• Sexual division of labor
  • Males may have focused on hunting and scavenging
  • Females may have focused on gathering and childcare
  • Cooperative provisioning of offspring and other group members
• Expansion out of Africa
  • Homo erectus first hominin to leave Africa ~1.8 million years ago
  • Spread across Asia and possibly into Europe
  • Required adaptations to new environments and climates

Debates and Ongoing Research

• Phylogenetic relationships between hominin species
  • Exact evolutionary relationships and lineages still debated
  • New fossil discoveries and analyses continue to refine our understanding
• Role of hunting vs. scavenging in early hominin diets
  • Degree to which early hominins actively hunted vs. scavenged meat from other predators' kills
  • Stable isotope analysis and archaeological evidence used to reconstruct diets
• Emergence of language and symbolic thought
  • When and how did complex language and symbolic thought emerge?
  • Anatomical, archaeological, and genetic evidence used to infer cognitive abilities
• Interbreeding between hominin species
  • Genetic evidence suggests interbreeding between modern humans, Neanderthals, and Denisovans
  • Raises questions about species boundaries and gene flow between hominin populations
• Environmental drivers of hominin evolution
  • Role of climate change, habitat variability, and other environmental factors in shaping hominin adaptations
  • Paleoclimatic and paleoecological data used to reconstruct ancient environments
• Earliest stone tool use and production
  • Recent evidence suggests stone tool use may have begun earlier than previously thought
  • Oldowan tools may have originated with australopithecines rather than early Homo
• Variability within hominin species
  • Recognition that hominin species were not homogeneous
  • Variability in morphology, behavior, and ecology within species
  • May reflect adaptation to local environments or cultural differences between populations