Primate Anatomy

Primate Behavior #

Social Interactions #

• k-selected: large body size, long life, few offspring — high investment
  • babies are completely dependent on parents (altricial)
    • maternal bond is just as important as nutrition
• estrus: a period where females are sexually receptive
  • a reproductive strategy
    • baboons, chimps, bonobos have estrus swelling
      • correlated w/ multi-male, multi-female social structures
      • correlated w/ large male reproductive organs
• sperm competition: a male reproductive strategy where males maximize the amount of sperm. Most seen w/ estrus swelling
• only lesser apes are monogamous
  • monogamy = low sexual dimorphism
  • single male polygynous = high

Human Reproductive Behavior #

• large reproductive organs ⇒ multimale/female
• little sexual dimorphism, small canines

Why Study Primates? #

• compare biological homologies, analogies

• shared behaviors (“culture”)

  • very complex backgrounds e.g. infanticide — not necessarily homologous

• Shared behaviors (“culture”)

  • very complex backgrounds e.g. infanticide - not necessarily homologous

• Shift to Great Ape Models

  • apes most similar biologically
  • chimps + bonobos most similar
  • behaviors not determined by biology alone

• Behavioral complexity

  • mirror recognition
  • tool manufacturing
  • linguistic capabilities

Socioecology #

Strepsirrhines: simple #

• Solitary, or pair bonding
• low sexual dimorphism + competition
• reliance on sense of smell

Anthropoids: complex #

• Highly social
• Cooperation

Field and Lab Studies #

• Field: observe social relations in large groups
  • communication, tools
• Lab: observe more complex behaviors, find out how capable primates are
  • mirror self-recognition, linguistics

complex behaviors, find out how capable primates are

• mirror self-recognition, linguistics

Pan-Homo Similarities #

1. Cooperation #

• Strong female-female bonds, male coalition

2. Ecology #

• Broad diet, fission-fusion societies

3. Culture #

• Hunting, tools

4. Communication #

5. Common Ancestor #

[M] Primate Anatomy #

Thursday, February 27, 2020 — 12:58 PM

Being Human #

• Humans, chimps share 98% DNA
• Humans are only apes w/ formal language
• Hox genes control differences in anatomical structures
  • make species look different
• Differences occur early in development
• Relatively large brain to body size ratio
  • Encephalization: deviation from expected brain size
    • all primates are encephalized, but humans to a much larger extent
• Brain develops before and after birth
  • most animals have developed brains at birth
  • due to small pelvic opening
  • babies become too costly for mothers to support for too long
• Does brain size matter?
  • Yes, but not the main factor
  • More important — how brain is organized and functions

Language: humans vs animals #

• open: can represent external phenomena | closed: cannot represent most external phenomena
• combinatorial: can combine ideas | non-combinatorial
• symbolic: idea-based, arbitrary | indexical
• controlled by cortex | controlled by limbic system (flight/fight)
  • lateralized into left brain
  • Wernicke’s Area: understanding
  • Broca’s Area: production
  • similar to other Great Apes
• hyoid bone: elevates larynx, allows speech

Unknown: Why is communication so important to humans? #

• chance mutation?
• slow evolution?
• do other animals have language?

The Skeleton #

• small brain

Comparative Anatomy: Face #

• flat face (Orthognathic) — Human
• eyebrow bone
• slanted face (Prognathic) — Chimpanzee
• big brain
• large canine

Comparative Anatomy: Brain Case #

• tiny face compared to brain
• Mastoid Process — bone that holds up muscles for our heavy head, bipedalism
• doglike extension — Chimpanzee

Comparative Anatomy: Dental Arcade #

• parallel — Chimpanzee
• parabolic — Human

Comparative Anatomy: Mandible #

• robust mandible — Orangutan
• gracile mandible — Human
• chin (humanlike feature)

Comparative Anatomy: Spider Monkey vs. Human Skeletons #

• tail, long arms, barrel chest
• flat chest, shoulder bones, long legs

Comparative Anatomy: Chimpanzee vs. Human Skeletons #

• Scapula on back
• No tail
• Short lower limbs
• Long arms
• Knuckle-walking hands

Bipedalism #

• ★ Humans are not the only bipedal animals…

Bipedalism in Other Animals #

• juvenile gorillas

Bipedalism in Other Animals #

• juvenile gorillas
• bonobos, chimps (occasional)
• dinosaurs, birds

…but humans are the only obligate bipeds

• only method of locomotion

Human Adaptations #

• head in midline of body
• upper body weight is centered on pelvis
• stable legs
• important: shape + orientation, not important: size

Bipedal Adaptations: Center of Gravity #

• Human = high center of gravity
• S-shape spinal cord

Human Bipedal Adaptations: Head #

• Foramen Magnum
  • Human: anterior
  • Great ape: posterior

Human Bipedal Adaptations: Vertebrae #

• S-shaped vertebral column

Human Bipedal Adaptations: Pelvis #

• Human = short, broad, bowl-shaped
• large muscle

Human Bipedal Adaptations: Femur — Human = angled femur

Human Bipedal Adaptations: Limb Proportions — legs are very large proportion of body

Human Bipedal Adaptations: Foot — Longitudinal Arch; Big toe = in line; toe used for grabbing

Why did humans become bipedal? #

• Thermoregulation hypothesis: limit exposure to heat/cold
• Savannah hypothesis: since more savannahs were created due to climate change, humans needed to figure out how to locomote there
• Male provisioning theory: bipedalism gives a reproductive advantage
  • Problem: assumes monogamy, but most primates are not
  • Support: no dimorphism in teeth

What We Do Know #

• Gradual evolution
• Early hominids: mixed locomotion