Document (#43407)

Author

DeSilva, J.M.
Traniello, J.F.A.
Claxton, A.G.
Fannin, L.D.

Title

When and why did human brains decrease in size? : a new change-point analysis and insights from brain evolution in ants

Source

Frontiers in ecology and evolution, 22 October 2021 [https://www.frontiersin.org/articles/10.3389/fevo.2021.742639/full]

Year

2021

Abstract

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.

Content

Vgl.: https://doi.org/10.3389/fevo.2021.742639.

Footnote

Vgl. auch: Rötzer, F.: Warum schrumpft das Gehirn des Menschen seit ein paar Tausend Jahren? Unter: https://krass-und-konkret.de/wissenschaft-technik/warum-schrumpft-das-gehirn-des-menschen-seit-ein-paar-tausend-jahren/. "... seit einigen tausend Jahren - manche sagen seit 10.000 Jahren -, also nach dem Beginn der Landwirtschaft, der Sesshaftigkeit und der Stadtgründungen sowie der Erfindung der Schrift schrumpfte das menschliche Gehirn überraschenderweise wieder. ... Allgemein wird davon ausgegangen, dass mit den ersten Werkzeugen und vor allem beginnend mit der Erfindung der Schrift kognitive Funktionen, vor allem das Gedächtnis externalisiert wurden, allerdings um den Preis, neue Kapazitäten entwickeln zu müssen, beispielsweise Lesen und Schreiben. Gedächtnis beinhaltet individuelle Erfahrungen, aber auch kollektives Wissen, an dem alle Mitglieder einer Gemeinschaft mitwirken und in das das Wissen sowie die Erfahrungen der Vorfahren eingeschrieben sind. Im digitalen Zeitalter ist die Externalisierung und Entlastung der Gehirne noch sehr viel weitgehender, weil etwa mit KI nicht nur Wissensinhalte, sondern auch kognitive Fähigkeiten wie das Suchen, Sammeln, Analysieren und Auswerten von Informationen zur Entscheidungsfindung externalisiert werden, während die externalisierten Gehirne wie das Internet kollektiv in Echtzeit lernen und sich erweitern. Über Neuimplantate könnten schließlich Menschen direkt an die externalisierten Gehirne angeschlossen werden, aber auch direkt ihre kognitiven Kapazitäten erweitern, indem Prothesen, neue Sensoren oder Maschinen/Roboter auch in der Ferne in den ergänzten Körper der Gehirne aufgenommen werden.
Die Wissenschaftler sehen diese Entwicklungen im Hintergrund, wollen aber über einen Vergleich mit der Hirnentwicklung bei Ameisen erklären, warum heutige Menschen kleinere Gehirne als ihre Vorfahren vor 100.000 Jahren entwickelt haben. Der Rückgang der Gehirngröße könnte, so die Hypothese, "aus der Externalisierung von Wissen und den Vorteilen der Entscheidungsfindung auf Gruppenebene resultieren, was zum Teil auf das Aufkommen sozialer Systeme der verteilten Kognition und der Speicherung und Weitergabe von Informationen zurückzuführen ist"."

Field

Kognitionswissenschaft

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