Primate Evolution and Human Characteristics

Vertebrate Evolution: Primates and Human Characters

Primate Diversity

  • Includes Langurs, Japanese macaques, Ringtail lemurs, Slow loris, Bushbabies, Chimps, Mountain gorillas, and Humans.

Primate Phylogeny

  • Archonta:
    • Includes Scandentia (Tree shrew), Dermoptera (Flying lemur), and Primates.
  • Euarchontoglires:
    • A larger group containing Archonta and Glires (Rodentia).
  • Boreoeutheria:
    • A superorder including Euarchontoglires and Laurasiatheria.
  • Afrotheria, Atlantogenata, and Placentalia are other major placental mammal groups.

Primate Characteristics

Skull Features
  • Large Brains: High encephalization quotient (EQ).
  • Reduced Snout: Decreased reliance on the sense of smell.
  • Forward-facing eyes: Stereoscopic vision crucial for arboreal existence; excellent color vision.
  • Post-orbital bar: Present for eye protection; post-orbital septa in Tarsiers, monkeys, and apes provide further protection.
Encephalization Quotient (EQ)
  • EQ=measured brain weight0.12∗(body weight)2/3EQ = \frac{measured \ brain \ weight}{0.12*(body \ weight)^{2/3}}
  • Homo sapiens: 7.5
  • Monkey: 4.0
  • Racoon: 1.3
  • Dog: 1.0
  • Rhino: 0.5
  • Mole: 0.5
Other Notable Features
  • Pentadactyly: Five fingers and five toes - a primitive placental mammal trait.
  • Grasping hands and feet: Opposable thumbs and big toes.
  • Nails: Present instead of hoofs or claws on at least one digit; monkeys and apes have nails on all digits.
  • Flexible limbs: Complete rotation of the arm around the shoulder, essential for arboreal living in monkeys and apes.

Primate Groups: Extinct and Extant

  • Primates (A)
    • Strepsirhini (C)
      • Lemuriformes.
      • Lorisiformes.
    • Haplorhini (E)
      • Tarsiiformes (F)
      • Anthropoidea (G)
        • Platyrrhini
        • Catarrhini (L)
          • Cercopithecoidea
          • Hominoidea
  • Extinct Groups
    • Plesiadapiformes.
    • Adapiformes.
    • Omomyidae.
    • Eosimiidae
    • Amphipithecidae
    • Parapithecoidea
    • Propliopithecoidea

Plesiadapiforms

  • Paleocene to mid-Eocene.
  • Elongate skulls with eyes on the side of the head.
  • Large incisors and diastema (rodent-like).
  • No post-orbital bar.
  • Claws, not nails.
  • Most lacked an opposable toe.

Living Strepsirrhines

  • Lemurs (Madagascar).
  • Lorises (Asia).
  • Pottos (Africa).
  • Bushbabies (Africa).
  • Shared Characteristics:
    • Moist nose.
    • Toothcomb.
    • Toilet claw on the second toe of the hind legs.
  • Evolved from Adapiformes in the Paleogene.

Adapiformes

  • Early Eocene to late Miocene.

Haplorhine Primates

  • Anthropoids: Monkeys and apes; 'higher primates'.
  • Tarsiiformes: Omomyids (extinct) and tarsiers; adaptations to leaping.

Early Anthropoids

  • Either Asian or African origin.
  • Extinct groups in Eocene and Oligocene.
  • Platyrrhines (New World monkeys) and Catarrhines (Old World monkeys and hominoids) split in the Eocene.
  • Aegyptopithecus: Oligocene, Egypt.

Old World vs. New World Monkeys

  • New World Monkeys (Platyrrhines):
    • Long tails; some are prehensile.
    • Poor thumb-and-finger grip.
  • Old World Monkeys (Cercopithecoids):
    • None have prehensile tails.
    • Better thumb-and-finger grip.

Apes (Hominoids)

  • Chimps, gorillas, orangutans, gibbons, and humans.
  • No tails; large bodies.
  • Big brains; possession of 'culture'.

Ape Evolution

  • Catarrhini (A)
    • Hominoidea (B)
      • Hylobatidae
      • Hominidae (D)
  • Proconsulidae.
  • Afropithecidae
  • Pongidae
  • Dryopithecini
  • Sahelanthropus
  • Orrorin
  • Sivapithecinae
  • Ardipithecus
  • Ponginae
  • Gorilla
  • Pan (Chimpanzee)
  • Australopithecus
  • Paranthropus
  • Homo

Proconsul

  • Lower Miocene, East Africa.
  • No tail.
  • Relatively large brain - 150cm3150cm^3.
  • Strengthened elbow joints for brachiation.
  • Small molars; large canines - primitive features.

Eurasian and African Apes

  • Divergence of brachiating living ape – Orangutan - and more terrestrial African apes.
  • Date of human-orang split 16-12 Ma from DNA.
  • Sivapithecus: Middle to late Miocene from Turkey and Asia.
  • Gigantopithecus: Late Miocene (India) to Pleistocene (China); HUGE - ~2.5m tall; possible origin of yeti stories.

African Origins

  • DNA differences:
    • gorilla-human: 1.62%.
    • chimp-human: 1.24%.
  • Split between gorilla and humans: 8.4 and 6.2 Ma.
  • Split between chimps and humans: 6.2 and 4.6 Ma.
  • Key point: This evolution took place exclusively in Africa.

Characteristics of Homo sapiens

  • Upright walking - bipedalism.
  • Large brains - highest encephalization quotient.
  • Speech.
  • Possession of ‘culture’ (e.g., altruism, writing, art, war).

Bipedalism

  • Entrance of spinal cord into skull (foramen magnum) beneath, not behind, the skull.
  • S-shaped spine - leads to bad backs!
  • Short bowl-shaped pelvis.
  • Long leg bones; straight hinge knees; flat feet with straight toes; big toe not opposable.

Trends in Primate Evolution

  • Increase in brain size in relation to body size.
  • Evolution of increasing behavioral complexity.
  • Eyes move to the front of the face for stereoscopic vision.
  • Increasing protection of eye sockets with bone.
  • Decrease in muzzle length; decrease in olfactory sense.
  • Increase in body size.
  • Nails replace claws.
  • Increase in gripping ability with opposable thumbs and toes.
  • Increase in parental investment in young.
  • Driven by living in forests - three-dimensional complexity requiring memory and spatial awareness for scattered resources.