Chapter 10: The Earliest Hominins 

Unique about homo Sapiens

  • Bipedal

  • teeth/jaw: wide parabolic dental arcade, small canines, large molars with thick enamel 

  • Large brains

  • Very slow life histories, long juvenile period

  • Talk and have elaborate symbolic culture 


Enamel: Thick enamel on a molar is good for crushing foods. It suggests an animal

used its teeth to grind seeds or crush the marrow out of bones.

Thin enamel on a molar, while delicate, causes sharp edges — perfect for

slicing and tearing foods like leaves and fruits

Very first hominins date back to 7 million years ago

Oldest hominin: Sahelanthropus tchadnesis

  • Chad, africa

  • Dated 6-7MA

  • Bipedal

  • Smaller canines than living apes

  • Chimp brain size (370 cc)

  • flattish face; large brow ridge

  • last common ancestor of pan and hominins

Bipedality based on spine 

  • human have s shaped spine for shock absorption and stability

  • human lumbar also larger for weight bearing

  • lumbar vertebrae curve forward

Bipedal Complex

  • Skull: Foramen magnum position towards center of skull.

  • Spine: A large and curved lower spine so that body is balanced above hips (lumbar lordosis).

  • Pelvis: Short and broad and laterally flared with changes in muscle attachments. tipped up like a bowl

  • Femur: Longer, stouter, angled towards the center-line, with larger joint surfaces.

  • Foot: Enlarged big toe in line with others, stiff midfoot, arch, nongrasping shorter toes

Orrorin tugenensis

  • kenya

  • dated 6 mya

  • mix of woodland and savanna

  • teeth chimp like but with thicker enamel

  • long curved fingers and robust arm bones so comfortable in trees

  • length of femur neck suggest balancing abductor mechanism

Ardipthecus ramidus

  • middle Awash, Ethiopia 4.4 mya

  • limb proportions intermediate between living apes and humans

  • bipedal

  • grasping foot (opposable big toe) but otherwise stiff foot

  • small chimp size brain

  • small canines, low sexual dimorphism

  • size between chimp and gorilla

  • Incisors smaller than chimps, ate less fruit

  • Molar: thicker enamel than apes but thinner than humans so harder diet, more nuts or seeds

  • canines not sharpened

  • Hand: not knuckle walking and when in trees walked on palms on top of trees

  • Foot: grasping toe with stiff foot

  • Pelvis had adaptations for walking and climbing

Bipedalism and canine reduction occurred first with brain expansion and language evolving later

Why Bipedalism:

  • more energetically efficient

  • thermoregulation: less surface exposed to sun, less solar radiation, more wind

  • free hands to carry food: helpful when food is in dangerous/exposed environment or in competition

Hominin Diversification 4 - 2 MYA (Pliocene)

  • all - africa

  • expanded range in Africa

  • small brains

  • bipedal

  • body size similar to chimps

  • body size sexual dimorphism but reduced canine dimorphism

  • thick molar enamel = hard foods

  • 3 genera: Australopithecus (only Pliocene), Paranthropus (starts in Pliocene) continues into Pleistocene, Homo (stars in Pliocene, continues into Pleistocene)

Australopithecines

  • lived in Pliocene (4.2 - 2 mya)

  • throughout Africa

  • skull and dentition intermediate between apes and humans

  • relatively large incisors (but smaller than modern apes)

  • Diastema, large jaw, and cheekbone

  • brain capacity larger than chimps but smaller than humans

  • live in woodland and grassland habitats

  • ate variety of foods

  • S shaped spine, pelvis, femur, and foot indicate fully bipedal when on ground

  • lower body indicated they climbed (maybe protection from predators or to sleep at night)

  • sexual dimorphism (males 50% larger than females, competition among males)

  • mature more rapidly than modern humans

Dikika Child (Australopithecus)

  • dikika, ethiopia

  • dated to 3.3 MA

  • 3 yr old female

  • bipedal and tree climbing

  • slower brain maturation than chimp

  • no vocal language

Lucy

  • 40% of complete skeleton

  • belonged to Au afarensis

hyoid bone important for speech, compare whether past species is more similar to chimps or modern human structure