Ch 8 Primate and Hominin Origins

Question 1

Dating Methods:

Relative Dating

Answer 1

“Tell if something is older or younger than something else, but doesn’t give exact dates”

Question 2

Dating Methods:
Relative Dating
- Stratigraphy
- Biostratigraphy 
- Paleomagnetism

Answer 2

Stratigraphy

• The lower layer (stratum) is older than the higher layer. Superimposition can be disturbed: volcanic activity, earthquakes/faulting, rivers & lakes
• Different layers can accumulate at vastly different rates

Biostratigraphy
- Use fossils with known dates from other nearby areas to date your layer (index fossils)

Paleomagnetism

• Based on known shifts in the earth’s geomagnetic pole
• Examine magnetically charged particles in rock as an ancient compass

Question 3

Dating Methods:

Chronometric (Absolute) Dating (2)

Answer 3

• Potassium (K)-Argon (Ar) dating
• Half-life of radioactive K-40 is 1.25 billion years after which half of its will have decayed into stable Ar-40
• Carbon-14 dating
• Half-life of 5,730 years
• Can only be used going back about 75 thousand years

Question 4

Hominid vs. Hominin

Answer 4

• Hominid reflects morphological/anatomical classification
  • Historically used term
• In this course use the term hominin

Question 5

What makes a hominin a hominin?

Answer 5

Three major changes
1. Obligate biped
2. Larger brain
3. Reduced and generalized teeth/jaws
Today most reliance put upon bipedalism
Large brains once considered preeminent hominin feature
- Now know they did not appear until 2-3 mya

Question 6

Why do we not fall over when we walk?

Answer 6

• Change in pelvis shape
• Shorter & broader, stabilize weight transmission
• Change in muscles
• Positions centre of mass over legs

Question 7

Anatomical features of bipedalism

Answer 7

• Foramen magnum position
• Shape of spine
• Shape/orientation of pelvis
• Angle of thigh bone (femur)
• Loss of opposability of big toe

Question 8

Facultative vs. obligate bipedalism

Answer 8

Facultative- can stand on two legs whenever you want

Obligate- is our normal and natural way to move

Question 9

Pros of Bipedalism:

Surveillance

Answer 9

Surveillance

- Especially in grassland, low shrub, open savanna

Question 10

Pros of Bipedalism:

Carrying objects

Answer 10

‘freeing of the hands’
- Food, sticks, stones, babies

Tripedalism
• Scientists propose this idea claiming that they may use three legs to walk, and the other to carry young

Question 11

Pros of Bipedalism:

Thremoregulation

Answer 11

• Upright posture (and hairlessness) beneficial in hot climates
• Less exposed surface area, convective/evaporative cooling
• Bipedal primates could walk farther from shade for longer periods of time to look for food

Question 12

Pros of Bipedalism:

Energetic Efficiency

Answer 12

• Bipedalism more efficient than quadrupedalism at slower speeds?
• Only with long legs, early hominins did not have long legs
• Studied humans and bipedal primates on a treadmill
• Human bipedalism was about 75% less costly in terms of energy use
• Due to the length of the legs- the longer they are the more efficient energy use

Question 13

Cons of Bipedalism:

3

Answer 13

Harder to pump blood to heart
- Greater likelihood of heart attack, stroke

Musculoskeletal problems

• ‘Fallen arches’ (feet)
• Prolapse of intervertebral discs
• Inguinal hernia

Childbirth

• Large brain and inflexible shoulder joint of infant
• Human infants must rotate 90° through midplane of birth canal