The Expensive-Tissue Hypothesis

Aiello, Leslie C.; Wheeler, Peter

doi:10.5040/9781474220095.ch-001

Cited by 52 publications

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“…This phenomenon has also been recognized in hominid evolution, where it is known as the "expensive tissue hypothesis" (Aiello and Wheeler 1995). Here, while selection has favored larger body size and brain in humans by hypermorphic extension of the growth period, the trade-off to evolve metabolically hungry brain tissue is the reduction of the size of the gut, the lower jaw, and teeth.…”

Section: Heterochrony and Developmental Trade-offsmentioning

confidence: 98%

Heterochrony: the Evolution of Development

2012

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Heterochrony can be defined as change to the timing or rate of development relative to the ancestor. Because organisms generally change in shape as well as increase in size during their development, any variation to the duration of growth or to the rate of growth of different parts of the organism can cause morphological changes in the descendant form. Heterochrony takes the form of both increased and decreased degrees of development, known as "peramorphosis" and "paedomorphosis," respectively. These are the morphological consequences of the operation of processes that change the duration of the period of an individual's growth, either starting or stopping it earlier or later than in the ancestor, or by extending or contracting the period of growth. Heterochrony operates both intra-and interspecifically and is the source of much intraspecific variation. It is often also the cause of sexual dimorphism. Selection of a sequence of species with a specific heterochronic trait can produce evolutionary trends in the form of pera-or paedomorphoclines. Many different life history traits arise from the operation of heterochronic processes, and these may sometimes be the targets of selection rather than morphological features themselves. It has been suggested that some significant steps in evolution, such as the evolution of vertebrates, were engendered by heterochrony. Human evolution was fuelled by heterochrony, with some traits, such as a large brain, being peramorphic, whereas others, such as reduced jaw size, are paedomorphic.

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Section: Heterochrony and Developmental Trade-offsmentioning

confidence: 98%

Heterochrony: the Evolution of Development

2012

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“…The human brain, in particular, has come to cost ∼20% of the total body resting metabolic rate, even though it represents only 2% of total body mass (M BD ), whereas, in other primates, the brain consumes a lower percentage of the body resting metabolic rate of approximately 9% (17). Even though a greater relative brain size in mammals has recently been found not to correlate with a smaller relative size of the digestive tract or other expensive organs (19), as predicted by the expensive-tissue hypothesis (10), increases in absolute brain size are expected to have direct metabolic consequences. The trend toward a larger brain size in primate evolution (20), particularly in the hominin lineage, has thus presumably occurred in the face of limitations imposed by the increasing metabolic cost of larger brains.…”

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confidence: 97%

“…The brain is the third most energy-expensive organ in the human body, ranking in total organ metabolic cost below only skeletal muscle and liver (9). Accordingly, several studies have suggested that the main constraints to increasing primate brain size in evolution are metabolic in nature (10)(11)(12)(13)(14)(15)(16)(17)(18). The human brain, in particular, has come to cost ∼20% of the total body resting metabolic rate, even though it represents only 2% of total body mass (M BD ), whereas, in other primates, the brain consumes a lower percentage of the body resting metabolic rate of approximately 9% (17).…”

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confidence: 99%

Metabolic constraint imposes tradeoff between body size and number of brain neurons in human evolution

Fonseca-Azevedo

Herculano‐Houzel

2012

Proc. Natl. Acad. Sci. U.S.A.

160

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Despite a general trend for larger mammals to have larger brains, humans are the primates with the largest brain and number of neurons, but not the largest body mass. Why are great apes, the largest primates, not also those endowed with the largest brains? Recently, we showed that the energetic cost of the brain is a linear function of its numbers of neurons. Here we show that metabolic limitations that result from the number of hours available for feeding and the low caloric yield of raw foods impose a tradeoff between body size and number of brain neurons, which explains the small brain size of great apes compared with their large body size. This limitation was probably overcome in Homo erectus with the shift to a cooked diet. Absent the requirement to spend most available hours of the day feeding, the combination of newly freed time and a large number of brain neurons affordable on a cooked diet may thus have been a major positive driving force to the rapid increased in brain size in human evolution.encephalization | expensive tissue hypothesis | brain metabolism T he human brain is a linearly scaled-up primate brain in its relationship between brain size and number of neurons (1), having evolved while being subjected to the same cellular scaling rules that apply to primates as a whole (2, 3), including great apes (4). With the largest brain among primates, humans thus have the largest number of neurons among these and possibly all mammals (5), a number that we estimate to be close to three times larger than in gorillas and orangutans, owners of the next largest brains among extant primates (4). We are not outstanding primates, on the contrary, in body size: gorillas can grow to be three times larger than humans. This discrepancy between body and brain size led to the predominant view that encephalization (that is, a larger brain size than expected for body size) is the main characteristic that sets humans apart from other primates and mammals as a whole (6). Although a relatively large brain compared with body size is expected to bring cognitive advantages (6), and despite the well-documented evidence for an increase in brain size during human evolution (7), there is still no consensus on what mechanisms or reasons led to brain enlargement in the Homo lineage.Why are the largest primates not those endowed with the largest brains as well? Rather than evidence that humans are an exception among primates, we consider this disparity to be a clue that, in primate evolution, developing a very large body and a very large brain have been mutually excluding strategies, probably because of metabolic reasons (4, 8). The brain is the third most energy-expensive organ in the human body, ranking in total organ metabolic cost below only skeletal muscle and liver (9). Accordingly, several studies have suggested that the main constraints to increasing primate brain size in evolution are metabolic in nature (10-18). The human brain, in particular, has come to cost ∼20% of the total body resting metabolic rate, even though it ...

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“…Given that larger bodies and brains are both metabolically expensive [1,2], and longer periods of lactation require greater calories per reproductive event for mothers [3], modern apes require a high-quality diet, and most meet this demand with ripe fruit in rainforests. Chimpanzees feed more on ripe fruits than do frugivorous (fruit-eating) monkeys sharing the same forest, and their diets are of higher quality than those of frugivorous monkeys when measured for carbohydrates, fibre and antifeedants [4,5].…”

Section: Introductionmentioning

confidence: 99%

Chimpanzee fauna isotopes provide new interpretations of fossil ape and hominin ecologies

Nelson

2013

Proc. R. Soc. B.

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Carbon and oxygen stable isotopes within modern and fossil tooth enamel record the aspects of an animal's diet and habitat use. This investigation reports the first isotopic analyses of enamel from a large chimpanzee community and associated fauna, thus providing a means of comparing fossil ape and early hominin palaeoecologies with those of a modern ape. Within Kibale National Park forest, oxygen isotopes differentiate primate niches, allowing for the first isotopic reconstructions of degree of frugivory versus folivory as well as use of arboreal versus terrestrial resources. In a comparison of modern and fossil community isotopic profiles, results indicate that Sivapithecus, a Miocene ape from Pakistan, fed in the forest canopy, as do chimpanzees, but inhabited a forest with less continuous canopy or fed more on leaves. Ardipithecus, an early hominin from Ethiopia, fed both arboreally and terrestrially in a more open habitat than inhabited by chimpanzees.

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The Expensive-Tissue Hypothesis

Cited by 52 publications

References 0 publications

Heterochrony: the Evolution of Development

Heterochrony: the Evolution of Development

Metabolic constraint imposes tradeoff between body size and number of brain neurons in human evolution

Chimpanzee fauna isotopes provide new interpretations of fossil ape and hominin ecologies

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