Human Evolution Notes

Human Evolution

Early Human History

  • The lecture discusses human evolution, referencing the movie "Caveman" as a humorous depiction of early human history.

Primate Characteristics

  • Primates share several key characteristics:

    • Grasping hands and feet with opposable thumbs and big toes.

    • Forward-facing eyes providing binocular vision.

    • Relatively large brains.

    • Increased parental care.

    • Complex social structures.

Primate Classification

  • Primates are classified into various families, including:

    • Hominidae (Great Apes, including humans)

    • Hylobatidae (Gibbons)

    • Cercopithecidae (Old World Monkeys)

    • Callitrichidae, Aotidae, Cebidae, Atelidae, Pitheciidae (New World Monkeys)

    • Tarsiidae (Tarsiers)

    • Daubentoniidae (Aye-ayes)

    • Cheirogaleidae, Lemuridae (Lemurs)

    • Lorisidae (Lorises)

    • Galagidae (Galagos)

  • The classification also includes suborders and infraorders like:

    • Strepsirrhini (Lemurs, Lorises, Galagos)

    • Haplorrhini (Tarsiers, Monkeys, Apes)

    • Simiiformes (Monkeys, Apes)

    • Catarrhini (Old World Monkeys, Apes)

    • Platyrrhini (New World Monkeys)

    • Hominoidea (Apes)

    • Cercopithecoidea (Old World Monkeys)

    • Tarsiiformes

    • Lemuriformes

    • Lorisiformes

    • Chiromyiformes

Divergence Times

  • Divergence times among primate groups are estimated using molecular and fossil data.

  • Examples:

    • Primates: ~80 million years ago

    • Great Apes (Hominoidea): ~20-30 million years ago

    • Old World Monkeys (Cercopithecoidea): ~20-30 million years ago

    • Lemurs: ~60-70 million years ago

New World vs. Old World Monkeys

  • Key differences exist between New World and Old World Monkeys:

    • New World Monkeys:

      • Prehensile tail.

      • Flat nose with side nostrils.

      • 36 teeth.

      • Limited social structure.

    • Old World Monkeys:

      • No prehensile tail.

      • Downward-facing nose nostrils.

      • 32 teeth (like humans).

      • Complex social structure.

Apes

  • Apes include:

    • Gibbons (20 species)

    • Orangutans (3 species)

    • Gorillas (2 species)

    • Chimpanzees (2 species)

    • Humans (1 species)

  • Apes are primarily found in Africa and Eurasia (Old World).

  • A defining characteristic of apes is the loss of a tail, attributed to a mutation in the brachyury gene.

  • Apes are divided into:

    • Lesser apes (Hylobatidae, i.e., Gibbons)

    • Great apes (Homonidae, i.e., Orangutans, Gorillas, Chimpanzees, Humans)

Timeline of Human Evolution

  • ~85 Mya: Common ancestor of primates (Late Cretaceous).

  • ~22 Mya: Common ancestor of apes (gibbons, orangutans, gorillas, chimpanzees, and humans).

  • ~18 Mya: Common ancestor of “great apes” (orangutans, gorillas, chimps, humans).

  • ~4-8 Mya: Split between ancestors of chimps and humans.

  • Approximate divergence times:

    • Hylobates (Gibbons): ~22 Mya

    • Pongo (Orangutan): ~18 Mya

    • Homo (Humans) / Pan (Chimps) split: ~6 Mya

The Miocene Epoch

  • The Miocene epoch is considered the "Golden Age" of Apes.

  • Early Miocene (22 million years ago): Many tree-adapted, non-monkey primate species existed across Southern Europe and Africa.

  • Approximately 100 species of apes are known from this period.

  • ~6-7 Mya: Split between Homo (human lineage) and Pan (chimpanzee lineage).

  • ~4-6 Mya: Development of bipedalism (walking on hind legs).

Bipedalism

  • Bipedalism is characterized by:

    • Curvature of the spine.

    • Scapula shifted toward the back.

    • Bowl-shaped pelvis.

    • Foramen magnum (the hole in the base of the skull where the spinal cord connects) positioned on the bottom of the head.

    • Thinner wrist bones.

  • Benefits:

    • Frees hands for tool and weapon use, as well as carrying things.

    • Raises head for better vision.

    • Energy efficiency in ground travel (e.g., on the savannah).

  • Costs:

    • Instability (more falls).

    • Back, knee, hip, and foot problems.

    • Hemorrhoids and varicose veins.

Early Hominins

  • Ardipithecus

    • 2 species.

    • 4-5 million years ago (early Pliocene).

    • Arboreal (tree-dwelling) but bipedal (“bowl-shaped” pelvis).

    • Feet still adapted for grasping.

    • Example: "Ardi" (A. ramidus).

  • Australopithecus

    • Australopithecus afarensis

      • Reduced canines and molars.

      • First modified stone tools.

      • Footprints in ash in Tanzania, dating back 3.9-2.9 million years ago, indicating full-time bipedalism.

      • Feet resemble later humans, with arched, non-grasping structure.

      • Hundreds of fossil specimens found in East Africa.

      • Example: Lucy, 3.2 mybp. 40% of skeleton was found. Bipedal, but small brain and anteriorly projecting face. Still climbed trees with long fingers, strong shoulders.

    • Australopithecus africanus

      • 3.3-2.1 mybp

        • Example: Little Foot. Most complete early hominid specimen, 90% intact

The Genus Homo

  • Origin: Approximately 2.75-2.80 million years ago.

  • Homo habilis

    • Evolved from an Australopithecus ancestor (Australopithecus is likely paraphyletic).

    • Large brain, small teeth (like humans).

    • Short femur, curved finger bones (like Australopithecus).

    • Greater use of stone tools, especially for butchering.

    • Possible migration