5. Human Evolution

Introduction to Human Evolution

  • Lengthy process of change by which people originated from apelike ancestors.
  • Evolved over approximately six million years.

Theories of Evolution

Lamarck's Theory of Inheritance of Acquired Characteristics

  1. Use and Disuse of Organs: Organs used frequently develop, unused ones deteriorate.
  2. Inheritance of Acquired Characteristics: Traits acquired during lifetime can be passed to offspring.
    • Example: Giraffe's long neck from stretching.

Darwin's Theory of Evolution by Natural Selection

  • Variation: Individuals within a population vary.
  • Inheritance: Variations are heritable.
  • Competition: Struggle for existence due to overproduction of offspring.
  • Survival of the Fittest: Individuals with advantageous traits survive and reproduce more.
    • Example: Peppered Moth adaptation to industrial pollution.

Human Ancestors: Key Characteristics

Hominin Cranial Capacity (cc) Key Features
Australopithecus 400-500 Bipedalism, reduced canines, sloping forehead.
Homo habilis 600-750 Fully bipedal, smaller canines, more upright posture.
Homo erectus 800-1100 Efficiently bipedal, prominent brow ridges, similar height to modern humans.
Neanderthals 1200-1750 Large cranial capacity, prominent brow ridges, adapted to cold (stocky).
Cro-Magnon 1400-1600 High forehead, reduced brow ridges, prominent chin, similar to modern humans.
Homo sapiens sapiens ~1350 High forehead, no prominent brow ridges, prominent chin, reduced body hair.