TF

Lecture 14: Early Hominins I

What Makes a Hominin a Hominin?

  • Definition: Hominins are species more closely related to Homo sapiens than to any living great ape.

Uniquely Human Features

  • Brain Size: Extremely large brain relative to body size.
  • Bipedalism: Anatomical features that support walking on two limbs.
  • Dentition: Very small canines and relatively flat faces (orthognathic vs prognathic).
  • Tool Use: Ability to modify raw materials into recognizable tool types.
  • Chin Development: Presence of a prominent chin.
  • Language: Capacity to learn and invent language.

Theories of Human Evolution

  1. Brain First Hypothesis:
  • Suggests the big brain is the most distinctive feature and evolved earliest.
  1. Bipedalism First Hypothesis:
  • Proposes that bipedal walking freed hands for tool use, driving brain expansion.

Early Hominins Overview

  • Homininae Subfamily: Includes Homo sapiens and fossil ancestors.
  • The hominin lineage diverged about 7-5 million years ago (Ma), with few fossils available from this early period.

Clusters of Early Hominins

  1. Pre-australopiths (7-4.4 Ma):
  • Example: Ardipithecus ramidus (~4.4 Ma)
  • Debate about full bipedalism.
  1. Earlier, Primitive Australopiths (4.2-3.0 Ma):
  • Example: Australopithecus afarensis (3.9-3.0 Ma)
  • Fully bipedal and gracile.
  1. Later, Derived Australopiths (2.5-1.0 Ma):
  • Example: Paranthropus (robust australopiths)
  • Fully bipedal and robust.

Detailed Study of Hominins

Sahelanthropus tchadensis

  • Age: Lived around 6-7 Ma, considered the oldest hominin.
  • Brain Size: Small (320-380 cc), similar to ape.
  • Derived Traits:
  • Intermediate foramen magnum position.
  • Smaller face and canines.
  • Intermediate enamel thickness.

Ardipithecus ramidus

  • Age: Approximately 4.4 Ma.
  • Brain Size: Similar to chimpanzee (~300-350 cc).
  • Anatomical Features:
  • Foramen Magnum: More anteriorly positioned for balance during bipedalism.
  • Pelvis: Short and broad with laterally oriented iliac blades, offering support for bipedal locomotion.
  • Opposable big toe indicating climbing capability.

Australopithecus afarensis ("Lucy")

  • Age: Approximately 3.9-3.0 Ma, with the famous specimen "Lucy" dated to 3.18 Ma.
  • Brain Size: Chimp-sized average 420 cc.
  • Footprints: Evidence of bipedalism found at Laetoli, Tanzania, dated 3.7 million years ago.
  • Dental Characteristics:
  • Canines intermediate in size between chimpanzees and humans.
  • Rounded dental arcade.

Australopithecus africanus

  • Age: 3.0-2.4 Ma, discovered as the Taung Child in 1924.
  • Cranial Capacity: ~450 cc.
  • Physical Traits:
  • Less prognathic face.
  • Reduced canines with parabolic dental arcade.

Robust Australopithecines (Paranthropus spp.)

  • Characteristics:
  • Adaptations for Heavy Chewing:
    • Large sagittal crest and massive post-canine teeth.
  • Three notable species:
    1. P. aethiopicus: Earliest robust species, discovered in Lake Turkana, Kenya.
    2. P. boisei: Discovered at Olduvai Gorge, notable for larger cranial capacity.
    3. P. robustus: Found in South Africa, notable for the largest cranial capacity in the genus.

Summary of Key Concepts

  • Early hominins provide important insights into human evolution leading up to modern humans.
  • Through anatomical studies and fossil evidence, we can trace the adaptations and changes that occurred during this significant period in our lineage.

Upcoming Classes

  • Lab 7: Scheduled for February 27/28.
  • Next Class: Lecture 15 on Early Hominins II.