In defense of the Expensive Tissue Hypothesis

Aiello, Leslie C.; Bates, Nicola; Joffe, Tracey H.

doi:10.1017/cbo9780511897085.006

Cited by 45 publications

(29 citation statements)

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“…Based on the similarity of allometric slopes with body mass, Armstrong (1983) and Hofmann (1983) were the first to suggest a direct metabolic constraint on brain size. The energetic viewpoint was largely abandoned for many years (but see Wheeler 1995, 1996;Aiello et al 2001) due to the rejection of the existence of a correlation between brain mass and BMR (McNab and Eisenberg 1989). However, this rejection was unjustified, partly due to a statistical error (Martin 1998) and partly due to an error in rodent brain mass data (see Isler and van Schaik 2006b).…”

Section: The Explanatory Power Of the Expensive Brain Hypothesismentioning

confidence: 99%

“…The Expensive Tissue hypothesis (Aiello and Wheeler 1995) examines tradeoffs among energy-hungry organs. Given the size of the organs involved, compensatory increases in brain size accompanying evolutionary reductions in gut size, should be the most profitable among them, and is indeed well supported for anthropoid primates (Aiello and Wheeler 1995;Fish and Lockwood 2003), although Aiello et al (2001) show that data selection and analytical technique substantially affect the results obtained. Also, the Expensive Tissue hypothesis was not confirmed for bats (Jones and MacLarnon 2004) or birds (Isler and van Schaik 2006a), perhaps because these latter taxa have small gastro-intestinal tracts.…”

Section: Introductionmentioning

confidence: 95%

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The Expensive Brain: A framework for explaining evolutionary changes in brain size

Isler

Schaik

2009

Journal of Human Evolution

395

419

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Section: The Explanatory Power Of the Expensive Brain Hypothesismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

The Expensive Brain: A framework for explaining evolutionary changes in brain size

Isler

Schaik

2009

Journal of Human Evolution

395

419

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“…Thus, reductions in organ or tissue mass could theoretically decrease the body's overall energy costs and compensate for the high metabolic demands of the brain. This perspective forms the basis of the Expensive Tissue Hypothesis, which posits that the increased metabolic requirement of an enlarged brain among hominids is offset by a concomitant reduction in gut size since both are metabolically "expensive" tissues (Aiello and Wheeler, 1995;Aiello, 1997;Aiello et al, 2001). …”

Section: Body Compositionmentioning

confidence: 99%

The Energetics of Encephalization in Early Hominids

Snodgrass

Leonard

Robertson

2009

The Evolution of Hominin Diets

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Bioenergetics, the study of the use and transfer of energy, can provide important insights into the ecology and evolution of early hominids. Despite a relatively large brain with high metabolic demands, contemporary humans and other primates have resting metabolic rates (RMRs) that are similar to those of other mammals. As a result, a comparatively large proportion of their resting energy budget is spent on brain metabolism among humans (~20-25%) and other primates (~8-10%) compared to other mammals (~3-5%). To understand this shift in energy budget, Aiello and Wheeler's Expensive Tissue Hypothesis (ETH) posits a metabolic trade-off-a reduction in gut size with brain size increase-to explain this phenomenon. Here, we explore the interrelationships between brain size, body size, diet, and body composition using comparative data for humans, non-human primates, and other mammals. Among living primates, the relative proportion of energy allocated to brain metabolism is positively correlated with dietary quality. Contemporary humans fall at the positive end of this relationship, having both a high quality diet and a large brain. Thus, high costs associated with the large human brain are supported, in part, by energy-rich diets. Although contemporary humans display relatively small guts, primates as a group have gut sizes that are similar to non-primate mammals. In contrast, humans and other primates have significantly less skeletal muscle for their size compared to other mammals. These comparative analyses suggest that alterations in diet quality and body composition were necessary conditions for overcoming the constraints on encephalization. Fossil evidence indicates that brain expansion with the emergence of Homo erectus at about 1.8 million years ago was likely associated with important changes in diet, body composition, and body size.

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“…ETH proposes gut reduction as a release mechanism on the metabolic constraints limiting encephalization, rather than a prime selective force for brain enlargement [20][21][22]. Consequently, brain size and diet quality may be asymmetrically associated.…”

Section: Discussionmentioning

confidence: 99%

Dietary quality and encephalization in platyrrhine primates

Allen

Kay

2011

Proc. R. Soc. B.

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The high energetic costs of building and maintaining large brains are thought to constrain encephalization. The 'expensive-tissue hypothesis' (ETH) proposes that primates (especially humans) overcame this constraint through reduction of another metabolically expensive tissue, the gastrointestinal tract. Small guts characterize animals specializing on easily digestible diets. Thus, the hypothesis may be tested via the relationship between brain size and diet quality. Platyrrhine primates present an interesting test case, as they are more variably encephalized than other extant primate clades (excluding Hominoidea). We find a high degree of phylogenetic signal in the data for diet quality, endocranial volume and body size. Controlling for phylogenetic effects, we find no significant correlation between relative diet quality and relative endocranial volume. Thus, diet quality fails to account for differences in platyrrhine encephalization. One taxon, in particular, Brachyteles, violates predictions made by ETH in having a large brain and low-quality diet. Dietary reconstructions of stem platyrrhines further indicate that a relatively high-quality diet was probably in place prior to increases in encephalization. Therefore, it is unlikely that a shift in diet quality was a primary constraint release for encephalization in platyrrhines and, by extrapolation, humans.

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In defense of the Expensive Tissue Hypothesis

Cited by 45 publications

References 0 publications

The Expensive Brain: A framework for explaining evolutionary changes in brain size

The Expensive Brain: A framework for explaining evolutionary changes in brain size

The Energetics of Encephalization in Early Hominids

Dietary quality and encephalization in platyrrhine primates

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