Evolution du cerveau

L’évolution du cerveau humain pose une multitude de questions. Sa chronologie, ses causes, ses facteurs limitants, ses conséquences…
Elle est liée notamment à la controverse « du feu ou de la viande » exposée dans cet article et les suivants, et plus succinctement dans ce thread twitter.
1. Données sur l’évolution du cerveau humain
2. Déterminants de l’évolution du cerveau

Données sur l’évolution du cerveau humain

L’évolution du cerveau est quantitative (un cerveau plus gros) et qualitative (la part relative de ses différentes parties évolue, des aires ou des réseaux différents s’organisent..).
Pour la partie quantitative, au moins deux aspects sont à considérer : la taille absolue du cerveau, et sa taille relative, avec la notion de coefficient d’encéphalisation.
Les méthodes employées sont diverses : mesure directe du volume intracrânien à partir des fossiles retrouvés, inférence de la forme du cerveau à partir des traces laisées à l’intérieur des boites crâniennes, ou mesure de la capacité d’irrigation sanguine de la boite crânienne…

When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants [Texte intégral]
Jeremy DaSilva
Frontiers in ecology and evolution, 2021

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.

The primitive brain of early Homo [PDF]
Ponce de Leon et al.
Science, 2021

Here, we show that the brains of early Homo from Africa and Western Asia (Dmanisi) retained a primitive, great apelike organization of the frontal lobe. By contrast, African Homo younger than 1.5 million years ago, as well as all Southeast Asian Homo erectus, exhibited a more derived, humanlike brain organization. Frontal lobe reorganization, once considered a hallmark of earliest Homo in Africa, thus evolved comparatively late, and long after Homo first dispersed from Africa.

Reconstructing the Neanderthal brain using computational anatomy [Texte intégral]
Koshiyama et al.
Nature scientific reports, 2018

We found that early Homo sapiens had relatively larger cerebellar hemispheres but a smaller occipital region in the cerebrum than Neanderthals long before the time that Neanderthals disappeared. Further, using behavioural and structural imaging data of living humans, the abilities such as cognitive flexibility, attention, the language processing, episodic and working memory capacity were positively correlated with size-adjusted cerebellar volume. As the cerebellar hemispheres are structured as a large array of uniform neural modules, a larger cerebellum may possess a larger capacity for cognitive information processing. Such a neuroanatomical difference in the cerebellum may have caused important differences in cognitive and social abilities between the two species and might have contributed to the replacement of Neanderthals by early Homo sapiens.

Pattern and process in hominin brain size evolution are scale-dependent [PDF]
Du et al.
The Royal Society Publishing, 2018

Our results show that fossil hominin ECV data at the clade level are most consistent with a gradual pattern of ECV increase through time. Understanding how this pattern emerged from processes that operate at lower taxonomic levels is more complicated. Our analyses are consistent with microevolutionary mechanisms as the dominant driver of clade-level change (64 or 88% of change using a more or less speciose taxonomy, respectively), alternating with secondary macroevolutionary mechanisms. This implies changing selective pressures and shifts in the relative importance of different evolutionary processes through time.
Body size, body proportions, and encephalization in a Middle Pleistocene archaic human from northern China [PDF]
Rosenberg et al.
PNAS, 2006
Rosenberg Body mass encephalization 2006
Les créationnistes aussi planchent sur l’évolution du cerveau :
Estimating the statistical significance of hominin encephalization [PDF]
TC Wood.
Journal of creation theology and science, 2016

A paleoneurological survey of Homo erectus endocranial metrics [PDF]
Bruner et al.
Quaternary international, 2015

The taxonomic debate on the phylogenetic coherence ofHomo erectus as a widespread intercontinental species is constantly put forward, without major agreements. Differences between the African and Asian fossil record as well as differences between the Chinese and Indonesian groups (or even within these two regions) have frequently been used to propose splitting taxonomical alternatives. In this paper, we analyze the endocranial variation of African and Asian specimens belonging to the hypodigm of H. erectus sensu lato, to assess whether or not these groups can be characterized in terms of traditional endocranialmetrics. According to the basic endocast proportions, the three geographic groups largely overlap in their phenotypic distribution and morphological patterns. The morphological affinity or differences among the specimens are largely based on brain size. As already evidenced by using other cranial features, traditional paleoneurological metrics cannot distinguish possible independent groups or trends within theAfro-Asiatic H. erectus hypodigm. Endocranial features and variability are discussed as to provide a general perspective on the paleoneurological traits of this taxon.
Brain ontogeny and life history in Pleistocene hominins [PDF]
Jean-Jacques Hublin et al.
The Royal Society Publishing, 2015
There is a consensus that Australopithecus endocasts show signs of brain reorganization and depart from the sulcal patterns found in apes, despite their ape-like endocranial volumes. It is therefore possible that brain reorganization in australopiths and its cognitive consequences underlie the subsequent brain expansion in the genus Homo. Furthermore, if supported by further investigations, the protracted pattern of brain development in A. afarensis would confirm that one cannot simply contrast a primitive ‘ape-pattern’ to a ‘human-pattern’.
Hublin 2015 évolution du cerveau

[Hominisation par la chasse]

How humans evolved large brains: comparative evidence [PDF]
Isler & Van Schaik
Evolutionary anthropology, 2014

In conclusion, the archeological evidence for big-game hunting or scavenging at an early stage in the evolution of the genus Homo points towards a major role of cooperative hunting, which led to male food sharing, as a trigger of the remarkable increase in hominin brain size. Provisioning and babysitting by post-reproductive females and communal nursing among breeding females may have pre- or postdated this change in lifestyle, but from the comparative evidence61 we suspect that female help on its own would not have allowed for the evolution of the uniquely human combination of traits that arose between 2.5 and 2
million years ago.

Scaling of brain and body weight within modern and fossil hominids:
implications for the Flores specimen [PDF]
P. Thomas Schoenemann, John S. Allen, 2006
The relationship between encephalization quotient (EQ) and body weight is found to be consistently negative within all hominid species
Suggère une première augmentation significative de l’encéphalisation avant -1,8Ma suivie d’un plateau, puis d’une seconde augmentation significative entre -600 et -150ka. L’une initiée par le passage à l’alimentation carnée, l’autre permise par le feu ?
Body mass and encephalization in pleistocene Homo [Abstract]
Ruff et al.
Nature, 1997

On the basis of an analysis of 163 individuals, body mass in Pleistocene Homo averaged significantly (about 10%) larger than a representative sample of living humans. Relative to body mass, brain mass in late archaic H. sapiens (Neanderthals) was slightly smaller than in early ‘anatomically modern’ humans, but the major increase in encephalization within Homo occurred earlier during the Middle Pleistocene (600–150 thousand years before present (kyr BP)), preceded by a long period of stasis extending through the Early Pleistocene (1,800 kyr BP).

Déterminants de l’évolution du cerveau

Evolution of the Human Brain: the key roles of DHA (omega-3 fatty acid) and Δ6-desaturase gene
Didier Majou
Oilseeds and fat crops and lipids, 2018

Cliquer pour accéder à ocl170035.pdf

How scientists perceive the evolutionary origin of human traits: Results of a survey study

Hanna Tuomisto et al.
Ecology and evolution, 2018
https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.3887

The hypotheses proposing that encephalization was triggered by improved nutrition also received intermediate popularity scores, whether achieved by cooking or by increased consumption of fish or meat (all three with credibility scores in the range 2.61–2.77).

The evolutionary roles of nutrition selection and dietary quality in the human brain size and encephalization
Roberto Carlos Burini, William R. Leonard
Nutrire, 2018

https://nutrirejournal.biomedcentral.com/articles/10.1186/s41110-018-0078-x

In addition to the energetic benefits associated with greater meat consumption, it appears that such a dietary shift would have also provided increased levels of key fatty acids necessary for supporting the rapid hominid brain evolution [60].

Half of human brain composition is fat, and 20% of its dry weight is long-chain polyunsaturated fatty acids (LCPUFAs). Consequently, improvements in consumption of dietary fat were a necessary condition for promoting encephalization [61, 62].

Mammalian brain growth is dependent upon sufficient amounts of two LCPUFAs: docosahexaenoic acid (DHA) and arachidonic acid (AA), and it appears that mammals have a limited capacity to synthesize these fatty acids from dietary precursors. Hence, species with higher levels of encephalization would have greater requirements for DHA and AA [62]. Consequently, dietary sources of DHA and AA were likely limiting nutrients that constrained the evolution of larger brain size in many mammalian lineages [63].

Meat and Nicotinamide: A Causal Role in Human Evolution, History, and Demographics
Adrian C Williams, Lisa J Hill
International Journal of Tryptophan Research, 2017
https://journals.sagepub.com/doi/pdf/10.1177/1178646917704661
Control of Fire in the Paleolithic: Evaluating the Cooking Hypothesis
Richard Wrangham, 2017
https://www.journals.uchicago.edu/doi/full/10.1086/692113
Primate brain size is predicted by diet but not sociality

DeCasien et al.
Nature ecology & evolution, 2017
https://www.nature.com/articles/s41559-017-0112

Here, we use a much larger sample of primates, more recent phylogenies, and updated statistical techniques, to show that brain size is predicted by diet, rather than multiple measures of sociality, after controlling for body size and phylogeny. Specifically, frugivores exhibit larger brains than folivores. Our results call into question the current emphasis on social rather than ecological explanations for the evolution of large brains in primates and evoke a range of ecological and developmental hypotheses centred on frugivory, including spatial information storage, extractive foraging and overcoming metabolic constraints.

Mais attention, ce résultat ne peut pas être étendu aux humains, dont le cerveau est trop atypique :

Humans excluded DeCasien 2017

Human Brain Expansion during Evolution Is Independent of Fire Control and Cooking
Alianda M. Cornelio et al.
Frontiers in neurosciences, 2016.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4842772/
https://core.ac.uk/download/pdf/82842463.pdf
Brain size and thermoregulation during the evolution of the genus Homo
Daniel E. Naya et al.
Comparative biochemistry and physiology, 2016
http://evolucion.fcien.edu.uy/daniel/paper66.pdf
Metabolic costs and evolutionnary implications of human brain development
Kuzawa et al.
Proceedings of the national academy of science, 2014
https://pdfs.semanticscholar.org/4a62/09020dcc73a1f6375bc5d24338aa22344f55.pdf
We find that the brain’s metabolic requirements peak in childhood, when it uses glucose at a rate equivalent to 66% of the body’s resting metabolism and 43% of the body’s daily energy requirement, and that brain glucose demand relates inversely to body growth from infancy to puberty. Our findings support the hypothesis that the unusually high costs of human brain development require a compensatory slowing
of childhood body growth.
Docosahexaenoic Acid and Shore-Based Diets in Hominin Encephalization: A Rebuttal
Cunnane et al.
American journal of human biology, 2007
https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajhb.20673
The Critical Role Played by Animal Source Foods in Human (Homo) Evolution
Katharine Milton, 2003
https://academic.oup.com/jn/article/133/11/3886S/4818038

The expensive-tissue hypothesis : the brain and the digestive system in human and primate evolution. Leslie Aiello, Peter Wheeler, 1995.
https://prod-edxapp.edx-cdn.org/assets/courseware/v1/67e06bd5c8a3c7b568a55bf3ee1933ee/c4x/WellesleyX/ANTH_207x/asset/Aiello95_expensivetissue_.pdf

Sur le rôle de l’alimentation dans l’évolution du cerveau, mais ici, plutôt les fruits, et pour les primates non humains (les humains sont exclus parce que la taille de leur cerveau est trop atypique) :
Primate brain size is predicted by diet but not sociality
Alex R. DeCasien et al.

Visuels

Graphique évolution du cerveau et acquisitions culturelles humaines
Bradshaw foundation, 2012, pour le visuel original.
http://bradshawfoundation.com/origins/index.php

Evolution du cerveau et maitrise du feu, d’après Bradshaw Foundation, 2012

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