Evolutionary Changes in Hominins

Foramen Magnum Position

  • Observation:

    • Chimpanzees: Foramen magnum is at the back of the skull.

    • Australopithecus & Humans: Foramen magnum is more underneath, near the middle of the skull.

  • What it means:

    • Underneath position indicates upright walking on two legs.

    • Back position indicates walking on all fours.

Cranial Capacity (Brain Size)

  • Observation:

    • Chimpanzees: Small brain (around 400cm3400 cm^3).

    • Australopithecus: Slightly bigger brain.

    • Humans: Much larger brain (up to 1400cm31400 cm^3).

  • What it means:

    • Brain size increased over time, aiding learning, problem-solving, and speech.

    • Bigger brains correlate with smarter species.

Face Projection (Prognathism)

  • Observation:

    • Chimpanzees: Faces stick out significantly.

    • Australopithecus: Less protruding face.

    • Humans: Flat face.

  • What it means:

    • Flatter face facilitates speech and accommodates a larger brain.

    • Suggests a change in diet to softer, cooked foods.

Brow Ridge

  • Observation:

    • Chimpanzees: Large brow ridge.

    • Human ancestors: Smaller brow ridge.

    • Modern humans: Barely any brow ridge.

  • What it means:

    • Skull changed shape to accommodate the growing frontal part of the brain (planning and thinking).

    • Brow ridge diminished as the brain became larger and more complex.

Teeth and Jaw Shape

  • Observation:

    • Chimpanzees: Big, sharp teeth and U-shaped jaw.

    • Humans: Smaller teeth and rounded jaw.

  • What it means:

    • Smaller teeth suggest a diet of softer, possibly cooked food.

    • Rounded jaw shape aided speech and reduced aggressive behavior.

Sagittal Crest

  • Observation:

    • Chimpanzees and some early hominins: Sagittal crest present.

    • Modern humans: No sagittal crest.

  • What it means:

    • Sagittal crest indicates strong jaw muscles used for chewing hard foods.

    • Humans' cooking practices eliminated the need for strong chewing muscles, leading to the disappearance of the crest.

Summary of Changes Over Time

  • Foramen Magnum (spine hole):

    • Chimpanzee: At the back.

    • Australopithecus: Closer to the middle.

    • Homo Species: Underneath skull. Shows walking upright.

  • Cranial Capacity (brain size):

    • Chimpanzee: Small.

    • Australopithecus: Bigger.

    • Homo Species: Largest. Shows getting smarter.

  • Face Projection (face sticks out):

    • Chimpanzee: Yes.

    • Australopithecus: Less.

    • Homo Species: Flat. Shows talking, bigger brain.

  • Brow Ridge (bone above eyes):

    • Chimpanzee: Big.

    • Australopithecus: Smaller.

    • Homo Species: Almost gone. Shows skull changed for brain.

  • Teeth & Jaw (tooth size, jaw shape):

    • Chimpanzee: Big teeth, U-shaped.

    • Australopithecus: Smaller teeth.

    • Homo Species: Small teeth, rounded jaw. Shows softer food, speech.

  • Sagittal Crest (top skull bone ridge):

    • Chimpanzee: Present.

    • Australopithecus: Sometimes.

    • Homo Species: None. Shows less need to chew hard food.