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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?. 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

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  1. Comparative Primatology and the Evolution of Human Life History Shannen Robson Department of Anthropology

  2. What is a primate?

  3. Primate distribution worldwide Humans expanded into non-tropical habitats

  4. Are humans primates?

  5. Or are we too distinct?

  6. Behavioral similarities ….

  7. Primate phylogeny • reflect shared ancestry • branch lengths reflect time

  8. Trichromatic: blues/greens & reds Bichromatic: blues/greens Eg., Trichromatic vision

  9. Ancestral state:Strepsirhini & Aotus mono- or bi-chromatic Polymorphic:Platyrrhini (NWM) -- X-linked Trichromatic:Howling monkeys & all catarrhines

  10. “.. 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

  11. 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

  12. Charnov’s Life History Invariant Model

  13. Compare great ape life histories • Longer lifespan & subadult period = larger body size • Age at last birth neutral • Reproductive rate faster than expected

  14. 1. Humans have the slowest life history

  15. Are old people a recent novelty? Oeppen & Vaupel (2002) Science 296:1029

  16. Stability of the old/young ratio Change life expectancy 3-fold &% of senior women in population varies little

  17. 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

  18. 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

  19. 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)

  20. 2. Neutral age at last birth Human reproductive pattern (Holman 1996)

  21. Births/female/year Compare chimp-human age-specific fertility Similarity suggests conserved, ancestral pattern

  22. 3. Fast reproductive rates OR By increasing her reproductive rate By increasing her litter size How can a female primate increase quantity?

  23. … nurse … carry … and wean Both result in multiple dependent offspring at the same time that she must … How can a mother manage?!

  24. For most primates, stacking is unsuccessful Usually she can’t Increased quantity compromises quality

  25. Callitrichids & humans increase quantitybecause they have help These primates are called‘cooperative breeders’

  26. AND increasing litter size postpartum estrus Callitrichids shorten intervals by …

  27. ‘stacking’ sequential dependents through early weaning via nonmaternal food-sharing Humans shorten interbirth intervals by …

  28. Who helps human moms feed kids?

  29. Male hunting? • Success is unpredictable • Hunter not “owner” • Wives & kids not favored • Must eat everyday!

  30. Gotta eat everyday! Postmenopausal females - Grandmothers

  31. 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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