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Cited by 474Animal Behavior and ReproductionPrimate Behavior and EcologyEvolution and Paleontology Studies

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

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Isler, Karin, van Schaik, Carel P.·2009·Journal of Human Evolution
DOI 10.1016/j.jhevol.2009.04.009
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Abstract

To explain variation in relative brain size among homoiothermic vertebrates, we propose the Expensive Brain hypothesis as a unifying explanatory framework. It claims that the costs of a relatively large brain must be met by any combination of increased total energy turnover or reduced energy allocation to another expensive function such as digestion, locomotion, or production (growth and reproduction). Focusing on the energetic costs of brain enlargement, a comparative analysis of the largest mammalian sample assembled to date shows that an increase in brain size leads to larger neonates among all mammals and a longer period of immaturity among monotokous precocial species, but not among the polytokous altricial ones, who instead reduce their litter size. Relatively large brained mammals, altricial and precocial, also show reduced annual fertility rates as compared to their smaller brained relatives, but allomaternal energy inputs allow some cooperatively breeding altricial carnivores to produce even more offspring in a shorter time despite having a relatively large brain. Thus, the Expensive Brain framework explains why brain size is linked to life history pace in some, but not all mammalian lineages. This framework encompasses other hypotheses of energetic constraints on brain size variation and is also compatible with the Brain Malnutrition Risk hypothesis, but the absence of a mammal-wide correlation between brain size and immature period argues against the Needing-to-Learn explanation for slower development among large brained mammals.

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Crossref · 10.1016/j.jhevol.2009.04.009

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  • Increased brain size in socially complex species may be associated with reduced brain operation costs.

    “Therefore, increased brain size in socially complex species may be associated with reduced brain operation costs, contrasting with the assumption that increased brain size increases metabolic costs (Aiello and Wheeler, 1995;Isler and van Schaik, 2009).”

    From When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants (2021) · cites this paper as Isler and van Schaik, 2009

  • An accelerated metabolic rate in the hominin lineage would be consistent with humans' high rate of reproduction and large brains relative to other apes.

    “An accelerated metabolic rate in the hominin lineage would be consistent with humans’ high rate of reproduction (7) and large brains (9, 11) relative to other apes.”

    From Metabolic adaptation for low energy throughput in orangutans. (2010) · cites this paper as [11]

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Authors
Isler, K., & van Schaik, C. P.
Affiliations
University of Zurich (CH)
Corresponding author
Isler, Karin
ORCID
Isler, Karin
Venue
Journal of Human Evolution
Publisher
Elsevier BV
Published
2009-10
Volume
57
Issue
4
Pages
392-400
ISSN
0047-2484 (ISSN-L)
DOI
10.1016/j.jhevol.2009.04.009
OpenAlex
W2061008199
Cited by
474
References
72
Citations by year
2026: 33 · 2025: 33 · 2024: 26 · 2023: 32 · 2022: 38 · 2021: 33 · 2020: 36 · 2019: 26 · 2018: 27 · 2017: 28 · 2016: 38 · 2015: 25 · 2014: 24 · 2013: 12 · 2012: 27
FWCI
21.19
Type
journal article
Language
en
Open access
Licence
Locations
  • Journal of Human Evolution (publishedVersion)
  • PubMed (publishedVersion)
  • Zurich Open Repository and Archive (University of Zurich) (acceptedVersion, other-oa)
  • Zurich Open Repository and Archive (University of Zurich) (submittedVersion, other-oa)
  • Zurich Open Repository and Archive (University of Zurich)
Topics
  • Life Sciences › Agricultural and Biological Sciences › Ecology, Evolution, Behavior and Systematics › Animal Behavior and Reproduction
  • Social Sciences › Psychology › Social Psychology › Primate Behavior and Ecology
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Evolution and Paleontology Studies
Keywords
brain size evolution, energy allocation, precociality, altriciality, litter size, fertility rate, allomaternal care, cooperative breeding, developmental delay, vertebrate brain evolution
MeSH terms
Aging, Animals, Brain, Breeding, Biological Evolution, Female, Growth, Humans, Learning, Litter Size, Male, Mammals, Organ Size, Phylogeny, Primates, Least-Squares Analysis, Malnutrition

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