Comparative primatology and the evolution of human life history
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Comparative Primatology and the Evolution of Human Life History. Shannen Robson Department of Anthropology. What is a primate?. Primate distribution worldwide. Humans expanded into non-tropical habitats. Are humans primates?. Or are we too distinct?. Behavioral similarities ….

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Comparative primatology and the evolution of human life history

Comparative Primatology and the Evolution of Human Life History

Shannen Robson

Department of Anthropology


What is a primate

What is a primate?


Primate distribution worldwide

Primate distribution worldwide

Humans expanded into non-tropical habitats


Are humans primates

Are humans primates?


Or are we too distinct

Or are we too distinct?


Behavioral similarities

Behavioral similarities ….


Primate phylogeny

Primate phylogeny

  • reflect shared ancestry

  • branch lengths reflect time


Eg trichromatic vision

Trichromatic: blues/greens & reds

Bichromatic: blues/greens

Eg., Trichromatic vision


Comparative primatology and the evolution of human life history

Ancestral state:Strepsirhini & Aotus mono- or bi-chromatic

Polymorphic:Platyrrhini (NWM) -- X-linked

Trichromatic:Howling monkeys & all catarrhines


Life histories

“.. lie at the heart of biology; no other field brings you closer to the underlying simplicities that unite and explain the diversity of living things and the complexities of their life cycles”

Life histories …

“LH theory evolution makes the simplifying claim that the phenotype consists of demographic traits connected by constraining relationships, trade-offs”.”

Stearns, 1992


Life history traits

Life history traits

  • size at birth

  • growth pattern

  • age at maturity

  • size at maturity

  • number, size, &

  • sex ratio of offspring

  • reproductive span

  • length of life


Charnov s life history invariant model

Charnov’s Life History Invariant Model


Compare great ape life histories

Compare great ape life histories

  • Longer lifespan & subadult period = larger body size

  • Age at last birth neutral

  • Reproductive rate faster than expected


1 humans have the slowest life history

1. Humans have the slowest life history


Are old people a recent novelty

Are old people a recent novelty?

Oeppen & Vaupel (2002) Science 296:1029


Stability of the old young ratio

Stability of the old/young ratio

Change life expectancy 3-fold &% of senior women in population varies little


Comparative primatology and the evolution of human life history

N Howell Demography of the

Dobe !Kung (Academic, 1979)

K Hill & AM Hurtado Ache

Life History (Academic, 1996)

NG Blurton Jones et al

AJHB 14, 184 (2002)

e0 = 30 & 33.5% adults >45

e0 = 33 & 40.4% adults >45

e0 = 37 & 39% adults >45

Survival of hunter-gatherers


Comparative primatology and the evolution of human life history

e0 = 15 & 2.2% adults >45

e0 = 33 & 40.4% adults >45

Compare chimp-human age-specific survival

1. Similar age decline in female fertility

2. Longer adult lifespans, later first birth

3. Much older population age structures


Age structure difference part of wider regularity compare humans chimps to macaques

80 - 84

75 - 79

70 - 74

65 - 69

Hadza juveniles (<15)

60 - 64

55 - 59

Hadza childbearing (15-45)

50 - 55

45 - 49

Hadza seniors (>45)

40 - 44

35 - 39

30 - 34

25 - 29

20 - 24

15 - 19

10 - 14

5 - 9

0 - 4

0

0.4

0.5

0.6

0.2

0.3

0.1

Age structure difference part of wider regularity:compare humans & chimps to macaques

Macaca fuscata (Arashiyama West) MSM Pavelka & LM Fedigan AJPA 109, 455 (1999)


2 neutral age at last birth

2. Neutral age at last birth

Human reproductive pattern (Holman 1996)


Comparative primatology and the evolution of human life history

Births/female/year

Compare chimp-human age-specific fertility

Similarity suggests conserved, ancestral pattern


How can a female primate increase quantity

3. Fast reproductive rates

OR

By increasing her reproductive rate

By increasing her litter size

How can a female primate increase quantity?


Both result in multiple dependent offspring at the same time that she must

… nurse

… carry

… and wean

Both result in multiple dependent offspring at the same time that she must …

How can a mother manage?!


Usually she can t

For most primates, stacking is unsuccessful

Usually she can’t

Increased quantity compromises quality


Callitrichids humans increase quantity because they have help

Callitrichids & humans increase quantitybecause they have help

These primates are called‘cooperative breeders’


Comparative primatology and the evolution of human life history

AND

increasing litter size

postpartum estrus

Callitrichids shorten intervals by …


Comparative primatology and the evolution of human life history

‘stacking’ sequential dependents

through early weaning

via nonmaternal food-sharing

Humans shorten interbirth intervals by …


Who helps human moms feed kids

Who helps human moms feed kids?


Male hunting

Male hunting?

  • Success is unpredictable

  • Hunter not “owner”

  • Wives & kids not favored

  • Must eat everyday!


Gotta eat everyday

Gotta eat everyday!

Postmenopausal females - Grandmothers


Grandmother hypothesis

1. Chimp-like life history; PlioPleistocene ecology

Grandmother hypothesis

2. More use of resources difficult for juveniles

3. More maternal provisioning

4. Females with declining fertility help

5. Vigorous perimenopausal females leave more descendants

6. Selection for slower aging, greater longevity

7. Longer adult lifespans; so later maturity, larger size

8. Expand into previously unoccupied habitats


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