When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants
Human brain size nearly quadrupled in the six million years since Homo last shared a common ancestor with chimpanzees, but human brains are thought to have decreased in volume since the end of the last Ice Age. The timing and reason for this decrease is enigmatic. Here we use change-point analysis t...
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| Format: | Article |
| Language: | English |
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Frontiers Media S.A.
2021-10-01
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| Series: | Frontiers in Ecology and Evolution |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/fevo.2021.742639/full |
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| author | Jeremy M. DeSilva Jeremy M. DeSilva James F. A. Traniello James F. A. Traniello Alexander G. Claxton Alexander G. Claxton Alexander G. Claxton Luke D. Fannin Luke D. Fannin |
| author_facet | Jeremy M. DeSilva Jeremy M. DeSilva James F. A. Traniello James F. A. Traniello Alexander G. Claxton Alexander G. Claxton Alexander G. Claxton Luke D. Fannin Luke D. Fannin |
| author_sort | Jeremy M. DeSilva |
| collection | DOAJ |
| description | Human brain size nearly quadrupled in the six million years since Homo last shared a common ancestor with chimpanzees, but human brains are thought to have decreased in volume since the end of the last Ice Age. The timing and reason for this decrease is enigmatic. Here we use change-point analysis to estimate the timing of changes in the rate of hominin brain evolution. We find that hominin brains experienced positive rate changes at 2.1 and 1.5 million years ago, coincident with the early evolution of Homo and technological innovations evident in the archeological record. But we also find that human brain size reduction was surprisingly recent, occurring in the last 3,000 years. Our dating does not support hypotheses concerning brain size reduction as a by-product of body size reduction, a result of a shift to an agricultural diet, or a consequence of self-domestication. We suggest our analysis supports the hypothesis that the recent decrease in brain size may instead result from the externalization of knowledge and advantages of group-level decision-making due in part to the advent of social systems of distributed cognition and the storage and sharing of information. Humans live in social groups in which multiple brains contribute to the emergence of collective intelligence. Although difficult to study in the deep history of Homo, the impacts of group size, social organization, collective intelligence and other potential selective forces on brain evolution can be elucidated using ants as models. The remarkable ecological diversity of ants and their species richness encompasses forms convergent in aspects of human sociality, including large group size, agrarian life histories, division of labor, and collective cognition. Ants provide a wide range of social systems to generate and test hypotheses concerning brain size enlargement or reduction and aid in interpreting patterns of brain evolution identified in humans. Although humans and ants represent very different routes in social and cognitive evolution, the insights ants offer can broadly inform us of the selective forces that influence brain size. |
| first_indexed | 2024-12-21T02:00:04Z |
| format | Article |
| id | doaj.art-1d912b51c1c241a3a96d21f2e38735a0 |
| institution | Directory Open Access Journal |
| issn | 2296-701X |
| language | English |
| last_indexed | 2024-12-21T02:00:04Z |
| publishDate | 2021-10-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Ecology and Evolution |
| spelling | doaj.art-1d912b51c1c241a3a96d21f2e38735a02022-12-21T19:19:39ZengFrontiers Media S.A.Frontiers in Ecology and Evolution2296-701X2021-10-01910.3389/fevo.2021.742639742639When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in AntsJeremy M. DeSilva0Jeremy M. DeSilva1James F. A. Traniello2James F. A. Traniello3Alexander G. Claxton4Alexander G. Claxton5Alexander G. Claxton6Luke D. Fannin7Luke D. Fannin8Department of Anthropology, Dartmouth College, Hanover, NH, United StatesEcology, Evolution, Environment, and Society, Dartmouth College, Hanover, NH, United StatesDepartment of Biology, Boston University, Boston, MA, United StatesGraduate Program in Neuroscience, Boston University, Boston, MA, United StatesDepartment of Anthropology, Boston University, Boston, MA, United StatesDepartment of Evolution, Ecology, and Organismal Biology, The Ohio State University, Columbus, OH, United StatesDepartment of Anatomy and Cell Biology, Oklahoma State University Center for Health Sciences, Tulsa, OK, United StatesDepartment of Anthropology, Dartmouth College, Hanover, NH, United StatesEcology, Evolution, Environment, and Society, Dartmouth College, Hanover, NH, United StatesHuman brain size nearly quadrupled in the six million years since Homo last shared a common ancestor with chimpanzees, but human brains are thought to have decreased in volume since the end of the last Ice Age. The timing and reason for this decrease is enigmatic. Here we use change-point analysis to estimate the timing of changes in the rate of hominin brain evolution. We find that hominin brains experienced positive rate changes at 2.1 and 1.5 million years ago, coincident with the early evolution of Homo and technological innovations evident in the archeological record. But we also find that human brain size reduction was surprisingly recent, occurring in the last 3,000 years. Our dating does not support hypotheses concerning brain size reduction as a by-product of body size reduction, a result of a shift to an agricultural diet, or a consequence of self-domestication. We suggest our analysis supports the hypothesis that the recent decrease in brain size may instead result from the externalization of knowledge and advantages of group-level decision-making due in part to the advent of social systems of distributed cognition and the storage and sharing of information. Humans live in social groups in which multiple brains contribute to the emergence of collective intelligence. Although difficult to study in the deep history of Homo, the impacts of group size, social organization, collective intelligence and other potential selective forces on brain evolution can be elucidated using ants as models. The remarkable ecological diversity of ants and their species richness encompasses forms convergent in aspects of human sociality, including large group size, agrarian life histories, division of labor, and collective cognition. Ants provide a wide range of social systems to generate and test hypotheses concerning brain size enlargement or reduction and aid in interpreting patterns of brain evolution identified in humans. Although humans and ants represent very different routes in social and cognitive evolution, the insights ants offer can broadly inform us of the selective forces that influence brain size.https://www.frontiersin.org/articles/10.3389/fevo.2021.742639/fullbrainevolutionanthomininHolocene |
| spellingShingle | Jeremy M. DeSilva Jeremy M. DeSilva James F. A. Traniello James F. A. Traniello Alexander G. Claxton Alexander G. Claxton Alexander G. Claxton Luke D. Fannin Luke D. Fannin When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants Frontiers in Ecology and Evolution brain evolution ant hominin Holocene |
| title | When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants |
| title_full | When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants |
| title_fullStr | When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants |
| title_full_unstemmed | When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants |
| title_short | When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants |
| title_sort | when and why did human brains decrease in size a new change point analysis and insights from brain evolution in ants |
| topic | brain evolution ant hominin Holocene |
| url | https://www.frontiersin.org/articles/10.3389/fevo.2021.742639/full |
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