Mechanical properties of plant underground storage organs and implications for dietary models of early hominins

Nathaniel J. Dominy, Erin Vogel, Justin D. Yeakel, Paul Constantino, Peter W. Lucas

Research output: Contribution to journalArticle

113 Citations (Scopus)

Abstract

The diet of early human ancestors has received renewed theoretical interest since the discovery of elevated δ13C values in the enamel of Australopithecus africanus and Paranthropus robustus. As a result, the hominin diet is hypothesized to have included C4 grass or the tissues of animals which themselves consumed C4 grass. On mechanical grounds, such a diet is incompatible with the dental morphology and dental microwear of early hominins. Most inferences, particularly for Paranthropus, favor a diet of hard or mechanically resistant foods. This discrepancy has invigorated the longstanding hypothesis that hominins consumed plant underground storage organs (USOs). Plant USOs are attractive candidate foods because many bulbous grasses and cormous sedges use C4 photosynthesis. Yet mechanical data for USOs-or any putative hominin food-are scarcely known. To fill this empirical void we measured the mechanical properties of USOs from 98 plant species from across sub-Saharan Africa. We found that rhizomes were the most resistant to deformation and fracture, followed by tubers, corms, and bulbs. An important result of this study is that corms exhibited low toughness values (mean = 265.0 J m-2) and relatively high Young's modulus values (mean = 4.9 MPa). This combination of properties fits many descriptions of the hominin diet as consisting of hard-brittle objects. When compared to corms, bulbs are tougher (mean = 325.0 J m-2) and less stiff (mean = 2.5 MPa). Again, this combination of traits resembles dietary inferences, especially for Australopithecus, which is predicted to have consumed soft-tough foods. Lastly, we observed the roasting behavior of Hadza hunter-gatherers and measured the effects of roasting on the toughness on undomesticated tubers. Our results support assumptions that roasting lessens the work of mastication, and, by inference, the cost of digestion. Together these findings provide the first mechanical basis for discussing the adaptive advantages of roasting tubers and the plausibility of USOs in the diet of early hominins.

Original languageEnglish (US)
Pages (from-to)159-175
Number of pages17
JournalEvolutionary Biology
Volume35
Issue number3
DOIs
StatePublished - Sep 1 2008

Fingerprint

storage organs
underground storage
mechanical properties
mechanical property
roasting
diet
corms
tuber
tubers
food
grass
grasses
bulbs
teeth
hunter-gatherer
C4 photosynthesis
enamel
animal tissues
Young modulus
Cyperaceae

All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics

Keywords

  • Australopithecus
  • Diet
  • Fracture toughness
  • Geophytes
  • Hypogeous plant foods
  • Paranthropus
  • Tubers
  • Young's modulus

Cite this

Dominy, Nathaniel J. ; Vogel, Erin ; Yeakel, Justin D. ; Constantino, Paul ; Lucas, Peter W. / Mechanical properties of plant underground storage organs and implications for dietary models of early hominins. In: Evolutionary Biology. 2008 ; Vol. 35, No. 3. pp. 159-175.
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Mechanical properties of plant underground storage organs and implications for dietary models of early hominins. / Dominy, Nathaniel J.; Vogel, Erin; Yeakel, Justin D.; Constantino, Paul; Lucas, Peter W.

In: Evolutionary Biology, Vol. 35, No. 3, 01.09.2008, p. 159-175.

Research output: Contribution to journalArticle

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