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Human Evolution Overview

Sep 15, 2025

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Overview

This lecture covers human evolution, focusing on anatomical differences between humans and African apes, shared traits, classification, and lines of evidence for a common ancestor among hominids.

Taxonomic Classification & Phylogenetics

  • Taxonomic hierarchy: Kingdom, Phylum, Class, Order, Family, Genus, Species.
  • Humans are classified as Homo sapiens (Genus capitalized, species lowercase, italicized or underlined).
  • Family Hominidae includes great apes and humans; Hominini includes humans, Ardipithecus, Australopithecus, and Homo.

Shared Characteristics: Humans & African Apes

  • Opposable thumbs; humans have precision grip, apes have power grip.
  • Both have two hands and two feet, each with five digits.
  • Long, rotating arms enable movement in any direction.
  • Naked fingertips with flat nails.
  • Reduced snout and weakened sense of smell.
  • Stereoscopic, color vision (forward-facing eyes).
  • Enlarged brain centers for hand-eye coordination.
  • No tails present.
  • Sexual dimorphism (males and females look distinct).
  • Molars and premolars have rounded cusps.

Anatomical Differences: Humans vs. African Apes

  • Bipedalism: Humans walk upright (bipedal); apes are knuckle-walkers (quadrupedal).
  • Foramen Magnum: Positioned centrally in humans, at the back in apes.
  • Spine Shape: S-shaped in humans (shock absorption), C-shaped in apes.
  • Pelvis: Human pelvis is short, wide, and supports body weight; ape pelvis is long and narrow.
  • Femur: Humans have a longer femur for upright walking.
  • Brain Size: Human brains are larger (~1.3-1.4 kg) than ape brains (~384-395 g).
  • Teeth & Jaw: Human canines and jaw size reduced; apes have large canines and pronounced gaps.
  • Palate Shape: Narrow in apes, U-shaped in Australopithecus, wide and curved in humans.
  • Prognathism: Apes have protruding jaws; humans have flat faces.
  • Cranial/Brow Ridges: Prominent in apes, reduced or absent in humans.

Evidence for Common Ancestry

  • Fossil Evidence: Shows gradual changes in anatomy (bipedalism, brain size, teeth, etc.).
  • Genetic Evidence: Chromosomal and mitochondrial DNA comparisons show close relationships; more similarities mean closer relation.
  • Mitochondrial DNA: Inherited maternally, traces ancestry back to "mitochondrial Eve."
  • Cultural Evidence: Tool use, fire, language, and art found in hominids; Homo habilis first to make stone tools.

Key Terms & Definitions

  • Bipedalism — Walking upright on two feet.
  • Foramen Magnum — Opening at the skull base where the spine attaches.
  • Prognathism — Forward projection of the jaw.
  • Sexual Dimorphism — Physical differences between male and female individuals.
  • Mitochondrial DNA (mtDNA) — DNA found in mitochondria, inherited from mother.

Action Items / Next Steps

  • Review diagrams of anatomical differences between humans and apes.
  • Read about Ardipithecus, Australopithecus, and Homo for evolutionary trends.
  • Practice interpreting phylogenetic trees and taxonomic classification.
  • Study tool types and their significance in hominid evolution.

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