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Cited by 177Pleistocene-Era Hominins and ArchaeologyPrimate Behavior and EcologyEvolution and Paleontology Studies

A shift toward birthing relatively large infants early in human evolution.

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DeSilva, Jeremy M.·2011·Proceedings of the National Academy of Sciences
DOI 10.1073/pnas.1003865108PMC PMC3024680
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Abstract

It has long been argued that modern human mothers give birth to proportionately larger babies than apes do. Data presented here from human and chimpanzee infant:mother dyads confirm this assertion: humans give birth to infants approximately 6% of their body mass, compared with approximately 3% for chimpanzees, even though the female body weights of the two species are moderately convergent. Carrying a relatively large infant both pre- and postnatally has important ramifications for birthing strategies, social systems, energetics, and locomotion. However, it is not clear when the shift to birthing large infants occurred over the course of human evolution. Here, known and often conserved relationships between adult brain mass, neonatal brain mass, and neonatal body mass in anthropoids are used to estimate birthweights of extinct hominid taxa. These estimates are resampled with direct measurements of fossil postcrania from female hominids, and also compared with estimates of female body mass to assess when human-like infant:mother mass ratios (IMMRs) evolved. The results of this study suggest that 4.4-Myr-old Ardipithecus possessed IMMRs similar to those found in African apes, indicating that a low IMMR is the primitive condition in hominids. Australopithecus females, in contrast, had significantly heavier infants compared with dimensions of the femoral head (n = 7) and ankle (n = 7) than what is found in chimpanzees, and are estimated to have birthed neonates more than 5% of their body mass. Carrying such proportionately large infants may have limited arboreality in Australopithecus females and may have selected for alloparenting behavior earlier in human evolution than previously thought.

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  • Australopithecus cranial capacities were on average 20% larger than those of late Miocene hominins Sahelanthropus and Ardipithecus or modern chimpanzees, despite having chimpanzee-sized bodies.

    “Australopithecus cranial capacities were on average 20% larger than those of the late Miocene hominins Sahelanthropus and Ardipithecus or modern chimpanzees, despite having chimpanzee-sized bodies (Wolpoff, 1999;Cartmill and Smith, 2009;DeSilva, 2011).”

    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 DeSilva, 2011

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Authors
DeSilva, J. M.
Affiliations
Boston University (US)
Corresponding author
DeSilva, Jeremy M.
ORCID
DeSilva, Jeremy M.
Venue
Proceedings of the National Academy of Sciences
Publisher
National Academy of Sciences
Published
2011-01-03
Volume
108
Issue
3
Pages
1022-1027
ISSN
  • 0027-8424 (ISSN-L)
  • 1091-6490
DOI
10.1073/pnas.1003865108
PMC
PMC3024680
OpenAlex
W2030722242
Cited by
177
References
81
Citations by year
2026: 14 · 2025: 3 · 2024: 4 · 2023: 7 · 2022: 11 · 2021: 11 · 2020: 15 · 2019: 20 · 2018: 5 · 2017: 15 · 2016: 11 · 2015: 12 · 2014: 6 · 2013: 17 · 2012: 21
FWCI
66.79
Type
journal article
Language
en
Open access
Locations
  • Proceedings of the National Academy of Sciences (publishedVersion)
  • PubMed Central (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • Johns Hopkins University
  • Yerkes National Primate Research Center, Emory University
Topics
  • Social Sciences › Anthropology › Pleistocene-Era Hominins and Archaeology
  • Social Sciences › Psychology › Social Psychology › Primate Behavior and Ecology
  • Physical Sciences › Earth and Planetary Sciences › Paleontology › Evolution and Paleontology Studies
Keywords
birth weight, human evolution, chimpanzees, Ardipithecus, Australopithecus, hominid evolution, female body mass, alloparenting, arboreality, locomotion, infant carrying
MeSH terms
Adult, Animals, Birth Weight, Body Weights and Measures, Brain, Biological Evolution, Female, Humans, Infant, Newborn, Organ Size, Hominidae

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