6: Human Biology

Paleocene - first primate-like species

Eocene - first primates (Strepsirrhines)

Oligocene - monkeys

Miocene - apes

Pliocene - first hominins

Pleistocene - Australopithecines and genus Homo

Holocene - agricultural revolution

Late Miocene → Pliocene:

• Himalayas created

• Africa + Eurasia joined

• East African rift formed

• Tropical forests shrank

• Grasslands and woodlands expanded

• Rapid fluctuations in temperature

Pliocene → Pleistocene:

• Cooling and drying

• Changes in vegetation and food sources

• Shift to higher meat consumption for survival

Late Pleistocene → Holocene:

• Warmer temperatures

Note:

• mya = millions of years ago

• kya = thousands of years ago

• ya = years ago

Scientific name is italicized, with genus capitalized

• Ex: Homo sapiens

Sometimes the genus is abbreviated

• Ex: H. sapiens

Pliocene hominins

• Species that lived during Pliocene epoch: Sahelanthropus tchadensis, Orrorin tugenensis, Ardipithecus kadabba, Ardipithecus ramidus

Australopithecines and genus Homo: Pleistocene epoch

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7 – 6 mya (million years ago), Chad

Oldest known hominin

Brain size and canines similar to chimpanzee

Large brow ridge

Thicker dental enamel

• More characteristic of humans than non-human primates

6 mya

No skull found

Humerus and femur suggest possible bipedalism

Similar to Ardipithecus ramidus, but older

• Larger canines than A. ramidus, but smaller than S. tchadensis

Possible evidence of bipedalism

Slightly larger brain size

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4.4 mya

First discovery named “Ardi”

Grasping foot

Adapted to tree-climbing and bipedalism

Smaller canines than A. kadabba

Genus: Australopithecus

Gracile Australopithecine species include:

• Australopithecus afarensis, Australopithecus africanus, Australopithecus sediba

Robust Australopithecine species include:

Australopithecus aethiopicus, Australopithecus boisei, Australopithecus robustus

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3.9 – 2.9 mya

First discovery named “Lucy”

Habitual bipedalism first appears

• Laetoli footprints – fossilized footprints provide evidence of bipedalism

Smaller canines and larger brain size than all the Pliocene hominins

Larger degree of sexual dimorphism than modern humans 

• Dimorphism seems to decrease in later species

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3.5 – 2 mya

Found in Southern Africa

Similar to A. afarensis

Smaller teeth and larger brain than A. afarensis

3D model

2 mya

Changes in humerus, femur, and pelvis

• Accommodating large-brained infants

Better precision grip

Larger brain size and smaller teeth than A. africanus

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2.7 – 2.3 mya

Oldest robust australopithecine

• Sagittal crest

• Megadont molars

• Large zygomatics (cheekbones)

Genus was once referred to as “Paranthropus,” but species have been reclassified in Australopithecus genus

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2.3 – 1.3 mya

Thickest dental enamel of all hominins

Robust australopithecine characteristics

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2 – 1 mya

Found in Southern Africa

Robust australopithecine characteristics

It seems like the evolution of early hominins lead to the evolution of the Australopithecines.  

The robust Australopithecines likely went extinct while gracile Australopithecine evolution lead to the evolution of genus Homo.

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2.4 – 1.5 mya

“Handy man”

Found with tool remains

Scavenging lifestyle

• Meat and bone marrow

• Carry away food to “home” base

Beginning of the Paleolithic era (Stone Age)

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1.9 mya – 143,000 years ago

Africa and Eurasia

Characterized by:

• Modern postcrania

• Slightly projecting face

• Pronounced supraorbital torus

• Medium-sized brain 

• Sagittal keel

• Long, low skull

• Occipital torus

• Shovel-shaped incisors

Important finds:

• Longest lived human species

• First species to migrate out of Africa

• First hand axe (more sophisticated tool)

• Fire use

• Ability to walk and run long distances

• Adapted to terrestrial lifestyle

• Possibly cared for elderly and sick individuals

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100,000 – 50,000 years ago

Island of Flores in Indonesia

• Short stature (smaller than Australopithecines)

• Small brain size compared to others (based on size alone), but increased intelligence

• Hunted, had advanced tool technology, and used fire

How did they get to the island?

• Did they ever come into contact with Homo sapiens? 

• How did they go extinct?

  • Volcanic eruption?  Did Homo sapiens drive them to extinction?

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700,000 – 200,000 yrs ago

Europe mostly, Africa

Larger brain case

Flatter face

Adapted to living in colder climates

• More muscular and robust body types

• Large supraorbital torus (brow ridge)

First species to routinely hunt and build shelters

Created wooden spears for hunting

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Neanderthals share 99.7% of DNA with H. sapiens

150,000 – 27,000 (?) years ago

Eurasia

Closest extinct human relative

Cold environment adaptations

Features:

• Robust body type

• Brains same size or even larger than H. sapiens

• Large mid-face

• Retromolar gap

• Double-arched supraorbital torus

• Occipital bun

• Large nose

Faster maturity rate than modern humans

• Fully grown by ~15 years

• Faster rate of enamel development on teeth

High adult mortality rate

• 40-45 years maximum

• Many skeletons show evidence of disease: arthritis, gum disease, fractures, stab wounds, withered limbs

Reproduction phase possibly sooner

Diet high in meat

Many survived serious injuries – suggests they cared for the ill and injured

May have practiced cannibalism

• Modern cannibalism is usually a type of ritual

• In Neanderthals, likely not ritual

• Krapina, Croatia – 130 kya

  • Long bones cracked for marrow, cut marks, burnt bones

• France – 100 kya

  • Same treatment of deer and hominin bones – scavenging marrow

Similar body-type as Neanderthals

Mostly in Siberia and Asia

Diverged from Neanderthals and humans around 1,313,500–779,300 years ago (modern humans and Neanderthals: 618–321,200 years ago)

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Anatomically modern Homo sapiens

• Same skeletal characteristics, different behavioral characteristics

Discovered in 1868 in France

• Physically tough life

• Fungal infections

• Several had fused vertebrae in necks due to traumatic injury (wounds healed over time)

• Survival based on group support and care?

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Dates back to 195,000 years ago in African continent

Common ancestor between Neanderthals and H. sapiens

Features:

• High, rounded cranium

• Tall, nearly vertical frontal bone

• Face under the cranium

• Large brain (average 1350 cc)

• Small teeth

• Less prognathism

• Smaller browridges

• Chin

Brain:

• Large, spherical

  • Connections between different parts of the brain are smaller -> faster, more complex connections

• Well-developed frontal lobe

• Well-developed language areas (Broca’s and Wernicke’s area)

• Motor strip of the brain is more developed

Cannot accurately compare H.N. with H.S., as a whole, because they lived in different environments

We can possibly compare H.N. with those H.S. that lived in the same region at the same time period

• Aurignacians (34,000 – 23,000 years ago, first modern humans in Europe)

• H.N. beads – associated with fewer than 10 types

• H.S. beads – associated with thousands of beads

H.N. vs H.S.

• H.N. less invested in social markings, possibly lived in smaller groups

• H.S. possibly lived in larger groups with more extensive trade networks