Anatomie, alimentation et éthologie comparées : humains, autres primates, mammifères

Il est souvent affirmé qu’Homo sapiens possède le même système digestif que les autres grands singes. Il est aussi affirmé qu’il possède une morphologie plus proche de celle des animaux herbivores que de celle des animaux carnivores. Il est par ailleurs parfois affirmé que les autres grands singes sont quasi exclusivement végétariens.
On retrouve notamment ces affirmations dans les vidéos très fortement médiatisées de Gary Yourofsky ou d’Irène Grosjean.
Qu’en est-il vraiment ?

1. Comparaison humain/autres animaux : alimentation
2. Comparaisons musculo-squeletiques
3.
Comportement alimentaire des primates


Comparaison humain/autres animaux : alimentation

Les humains ont évolué pour métaboliser mieux les lipides, les chimpanzés ont évolué pour métaboliser mieux les glucides :

Comparative analyses of chromatin landscape in white adipose tissue suggest humans may have less beigeing potential than other primates
Smain-Lenz et al.
Genome biology and evolution, 2019
https://www.biorxiv.org/content/biorxiv/early/2019/01/18/524868.full.pdf

Taken together, these results suggest that humans shut down regions of the genome to accommodate a high fat diet while chimpanzees open regions of the genome to accommodate a high sugar diet.

Une comparaison générale de l’acidité de l’estomac de plusieurs dizaines d’animaux, dont il ressort que l’estomac humain est en fait anormalement acide pour un omnivore, son acidité plaçant en fait Homo sapiens quelque part entre les carnivores et les charognards. Autre indice suggérant une part importante du charognage ou de la consommation de proies longtemps après capture dans l’histoire évolutive humaine :

The Evolution of Stomach Acidity and Its Relevance to the Human Microbiome
Deanna E. Beasley et al, 2015
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.013411

Variable responses of human and non-human primate gut microbiomes to a Western diet
Amato et al.
Microbiome, 2015
https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-015-0120-7

Results

Here, we show that the human microbiome reacts differently to a high-protein, high-fat Western diet than that of a model primate, the African green monkey, or vervet (Chlorocebus aethiops sabaeus). Specifically, humans exhibit increased relative abundance of Firmicutes and reduced relative abundance of Prevotella on a Western diet while vervets show the opposite pattern. Predictive metagenomics demonstrate an increased relative abundance of genes associated with carbohydrate metabolism in the microbiome of only humans consuming a Western diet.

Conclusions

These results suggest that the human gut microbiota has unique properties that are a result of changes in human diet and physiology across evolution or that may have contributed to the evolution of human physiology. Therefore, the role of animal models for understanding the relationship between the human gut microbiota and host metabolism must be re-focused.

Cette étude suggère que la surface d’absorption du système digestif humain serait en réalité bien plus petite qu’on ne le pensait, ce qui ne va pas dans le sens d’une importante consommation végétale (avec la réduction globale du volume, la réduction relative très importante du côlon, et les modifications du microbiotes au cours de l’évolution humaine, voir plus bas).

Surface area of the digestive tract – revisited
Helander et Fändricks.
Scandinavian journal of gastroenterology, 2014
https://www.tandfonline.com/doi/abs/10.3109/00365521.2014.898326?journalCode=igas20

Results. Literature review of intubation or radiological methods indicates an oroanal length of ∼5 m, two-third of which refers to the small intestine. However, there is a considerable variation between individuals. The inner diameter of the small intestine averages 2.5 cm and that of the large intestine averages 4.8 cm. The mucosa of the small intestine is enlarged ∼1.6 times by the plicae circulares. Morphometric data obtained by light and electron microscopy of biopsies demonstrate that villi and microvilli together amplify the small intestinal surface area by 60–120 times. Surface amplification due to microvilli in the colon is ∼6.5 times. The mean total mucosal surface of the digestive tract interior averages ∼32 m2, of which about 2 m2 refers to the large intestine. Conclusion. The total area of the human adult gut mucosa is not in the order of tennis lawn, rather is that of half a badminton court.

Le microbiome des humains modernes est très différent de ce qu’il était il y a quelques millions d’années, et très différent de celui des autres primates, plus adapté à une consommation de produits animaux.

Rapid changes in the gut microbiome during human evolution.
Andrew H. Moellera & al., 2014.
http://www.pnas.org/lookup/doi/10.1073/pnas.1419136111

Relative to the microbiomes of wild apes, human microbiomes have lost ancestral microbial diversity while becoming specialized for animal-based diet

Il est parfois affirmé que les lions ont un système digestif très court, de seulement 2m.
Ce n’est pas vrai. La longueur absolue du système digestif des lions est proche de celle des humains. En revanche, la longueur du corps d’un lion est à peu près deux fois celle d’un humain, donc un ratio longueur des intestins/longueur du corps plus faible chez le lion (ce qui semble normal pour un carnivore pur).
Aspects of Carcass Digestibility by African Lions (Panthera leo Linnaeus, 1758) under Captive Conditions
Y. Smith et al.

Pakistan Journal of Biological Sciences, 2006.
https://scialert.net/fulltextmobile/?doi=pjbs.2006.2149.2152

Smith et al. 2003 panthera leo intestine length

Les intestins humains diffèrent significativement des intestins des autres primates, notamment dans le volume relatif de l’intestin grêle (beaucoup plus grand chez sapiens) et dans le volume relatif du côlon (beaucoup plus petit chez sapiens), laissant entendre une adaptation à une alimentation sensiblement plus carnée. Du fait d’un volume global plus faible du système digestif dans son ensemble (voir plus bas), en réalité, le volume global du côlon humain rapporté au volume du corps entier est environ 4 fois plus faible :

Nutritional Characteristics of Wild Primate Foods: Do the Diets of Our Closest Living Relatives Have Lessons for Us?
Katharine Milton, 1999
http://linkinghub.elsevier.com/retrieve/pii/S0899900799000787
http://www.direct-ms.org/wp-content/uploads/2018/01/primaten.pdf
Milton 1999 compared guts

 

Selon cette étude, il semble difficile d’affirmer que la longueur des intestins humains soit plus proche de celle des herbivores que de celle des carnivores. En réalité, elle semble assez similaire à celle du chien, et pas très éloignée de celle du chat :

Human adaptations to meat eating. 
Henneberg, M., Sarafis, V., & Mathers, K., 1998.
https://sci-hub.tw/https://link.springer.com/article/10.1007/BF02436507

Henneberg 1998 human adaptations meat length

Le volume relatif des intestins humains est nettement plus faible que celui des autres primates. Cela laisse supposer une adaptation à une alimentation beaucoup plus riche.

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

Proportion comparée des organes primates et humains

On sait depuis longtemps que la longueur de l’intestin n’est qu’une donnée relative, qui ne peut avoir qu’un caractère indicatif.

Des variations de longueur de l’intestin
Block, 1904
https://www.persee.fr/doc/bmsap_0037-8984_1904_num_5_1_7864

Block 1904 longueur intestins


Comparaisons musculo-squeletiques

Chimpanzee super strength and human skeletal muscle evolution
O’Neil et al.
PNAS 2017
https://www.pnas.org/content/pnas/114/28/7343.full.pdf

Since at least the 1920s, it has been reported that common chim-panzees (Pantroglodytes) differ from humans in being capable of exceptional feats of “super strength” both in the wild and in captive environments. A mix of anecdotal and more controlled studies provides some support for this view; however, a critical review of available data suggests that chimpanzee mass-specific muscular performance is a more modest 1.5 times greater than humans on average […] Computer simulations of species-specific whole-muscle models indicate that maximum dynamic force and power output is 1.35 times higher in a chimpanzee muscle than a human muscle of similar size. […] . We propose that the hominin lineage experienced a decline in maximum dynamic force and power output during the past 7–8 million years in response to selection for repetitive, low-cost contractile behavior.

Le lancer particulièrement efficace de projectiles n’est pas qu’une simple compétence humaine, c’est aussi le résultat d’un ensemble d’adaptations anatomiques.

Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo
Roach et al.
Nature, 2013
https://www.nature.com/articles/nature12267

Here we use experimental studies of humans throwing projectiles to show that our throwing capabilities largely result from several derived anatomical features that enable elastic energy storage and release at the shoulder. These features first appear together approximately 2 million years ago in the species Homo erectus. Taking into consideration archaeological evidence suggesting that hunting activity intensified around this time9, we conclude that selection for throwing as a means to hunt probably had an important role in the evolution of the genus Homo.

Depuis Homo erectus, les humains possèdent des membre inférieurs beaucoup plus longs et droits que ceux de leurs cousins primates. Associée à de meilleurs capacités de respiration durant la course et à de meilleures capacités de sudation et de régulation thermique, cette évolution fait d’eux de redoutables coureurs d’endurance.
Pour l’ensemble des adaptations humaines à la course d’endurance, voir cette page.

Ici, les auteurs insistent sur les évolutions qu’ils attribuent à la maîtrise du feu, mais l’allongement des membres inférieurs est bien visible sur l’une de leurs illustrations :

Human Adaptation to the Control of Fire
Richard Wrangham & Rachel Carmody
Evolutionnary anthropology, 2010
https://dash.harvard.edu/bitstream/handle/1/8944723/human_adaptation_to_the_control.pdf?sequence=1

Wrangham Carmody 2010


Comportement alimentaire des primates

New Observations of Meat Eating and Sharing in Wild Bonobos (Pan paniscus) at Iyema, Lomako Forest Reserve, Democratic Republic of the Congo
Wakefield et al.
Folia primatologica, 2019
https://www.karger.com/Article/Abstract/496026

This report contributes to a growing body of data suggesting that wild bonobos consume meat at higher rates than previously thought, female control of carcasses is frequent but not exclusive, and meat sharing in bonobos is primarily passive but not without aggression.

Les macaques ne laissent pas leur part de viande aux chiens. Ils ont une prédilection pour le rat. A tel point que dans les plantations de palmiers, une étude suggère que leur effet régulateur sur les rats est supérieur à leurs nuisances sur les végétaux.

Macaques can contribute to greener practices in oil palm plantations when used as biological pest control
Holtzner et al.
Current biology, 2019
https://www.sciencedirect.com/science/article/pii/S0960982219311716

wild macaques have the potential to act as biological pest control by feeding on plantation rats, the major pest for oil palm crops, with each macaque group estimated to reduce rat populations by about 3,000 individuals per year

Des chimpanzés sont capables de voler leur proie à des prédateurs de taille moyenne à grande. Cela renforce l’idée que les préhumains et premiers représentants du genre Homo étaient capables de faire de même.

Wild chimpanzees deprived a leopard of its kill: Implications for the origin of hominin confrontational scavenging
Nakamura et al.
Journal of human evolution, 2019
https://www.sciencedirect.com/science/article/pii/S0047248418303658

Chimpanzees do scavenge meat, although rarely, but no previous evidence of confrontational scavenging has hitherto emerged. Thus, it was assumed that they are averse to confrontation with even leopard-sized predators. However, in the observed case the chimpanzees frequently emitted waa barks, which indicated that they were aware of the leopard’s presence but they nevertheless continued to eat the scavenged meat. In addition, we compiled and reviewed 49 cases of chimpanzee encounters with animal carcasses in the Mahale Mountains of Tanzania in 1980–2017. Chimpanzees scavenged meat in 36.7% of these cases, and tended to eat the meat when it was fresh or if the animal species was usually hunted by chimpanzees. However, no evidence indicated that carcasses were avoided when leopard involvement was likely. These results suggest that chimpanzee-sized hominins could potentially confront and deprive leopard-size carnivores of meat.

Les chimpanzés mangent leurs jeunes proies en commençant par la cervelle, qui est la partie nutritionnellement la plus prisée.

Meat Eating by Wild Chimpanzees (Pan troglodytes schweinfurthii): Effects of Prey Age on Carcass Consumption Sequence
Ian C. Gilby & Daniel Wawrzyniak
International journal of primatology, 2018
https://link.springer.com/article/10.1007/s10764-018-0019-9

Overall, the head was significantly more likely to be targeted first than either the torso (including viscera) or appendages. This result was driven by subadult prey, 91% of which were eaten head-first, probably because their skulls were relatively easy for chimpanzees to break with a single bite.

Mammals consumed by bonobos (Pan paniscus): new data from the Iyondji forest, Tshuapa, Democratic Republic of the Congo
Sakamaki et al.
Primates, 2016
https://link.springer.com/content/pdf/10.1007%2Fs10329-016-0529-z.pdf

We found evidence thatIyondji bonobos consumed duikers (Cephalophus dorsalis,C. monticola) and diurnal monkeys (Cercopithecus asca-nius), which is notable because only anomalures (Anoma-lurusspp.) are consumed by bonobos in Wamba, a long-term study site established in 1973, located in an areaadjacent to Iyondji.

Certains chimpanzé chassent avec des outils, notamment des femelles, et notamment dans des environnements de savane.

New evidence on the tool-assisted hunting exhibited by chimpanzees (Pan troglodytes verus) in a savannah habitat at Fongoli, Sénégal
Pruetz et al.
Royal Society Open Science, 2015
https://royalsocietypublishing.org/doi/full/10.1098/rsos.140507

Here, we test the hypothesis that sex and age patterns in tool-assisted hunting (n=308 cases) at Fongoli occur and differ from chimpanzees elsewhere, and we compare tool-assisted hunting to the overall hunting pattern. Males accounted for 70% of all captures but hunted with tools less than expected based on their representation on hunting days. Females accounted for most tool-assisted hunting. We propose that social tolerance at Fongoli, along with the tool-assisted hunting method, permits individuals other than adult males to capture and retain control of prey, which is uncommon for chimpanzees. We assert that tool-assisted hunting could have similarly been important for early hominins.

Primate hunting by bonobos at LuiKotale, Salonga National Park
Martin Surbeck & Gottfried Hohmann
Current Biology, 2008
https://www.cell.com/current-biology/fulltext/S0960-9822(08)01117-2?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0960982208011172%3Fshowall%3Dtrue

Chimpanzees (Pan troglodytes) and bonobos (P. paniscus) hunt and consume the meat of various mammals. While chimpanzees frequently hunt in groups for arboreal, group-living monkey species, bonobos are thought to focus on medium-sized terrestrial prey, such as forest antelopes, squirrels and other rodents, which are caught opportunistically by single individuals. The absence of monkey hunting by bonobos is often used to illustrate the divergent evolution of the two Pan species. Here, we present the first information on hunting of diurnal, arboreal and group living primates by wild bonobos.

Selon les

lieux, les chimpanzés peuvent consommer des quantités de viande importante. Les mâles en consomment nettement plus que les femelles.

Chimpanzee Hunting Behavior
The 45 Gombe chimpanzees of the Kasakela community in 1992 consumed over 500 kg of red colobus meat, and their total meat consumption for the year was probably close to 700 kg. The previous year (1991), colobus meat consumption was less than 200 kg, and in 1988, this figure was less than 150 kg (Stanford 1998). Averaged over years, the level of consumption in the 1980s and 1990s seems similar to the estimate of 441 kg of meat per year for the same community in the 1970s (Wrangham and van Zinnicq Bergmann Riss 1990; Stanford 1998).
Boesch and Boesch‐Achermann (2000) estimate that, averaged across the year, male Taı chimpanzees consume 186 g per day, while females consume 25 g per day. Their estimates for Gombe chimpanzees, similarly averaged, are 55 g per day for males and 7 g per day for females. These are similar to estimates made by Stanford (1998) of 70 g per day for males during peak hunting season and by Wrangham (1975) of 22 g averaged over males and females.
Les gorilles consomment des quantités plus ou moins importantes d’insectes.
Intrapopulation differences in ant eating in the mountain gorillas of Bwindi Impenetrable National Park, Uganda
Jessica Ganas & Martha M. Robbins, 2004

Selon cette étude, deux listes sont bien fournies : la liste des primates qui chassent (et qui chassent des mammifères), et la liste de leurs proies, dont font parfois partie… des enfants humains :

Le singe carnivore. La chasse chez les primates non humains.
Jacqueline Ducros, Albert Ducros, 1992.
http://www.persee.fr/doc/bmsap_0037-8984_1992_num_4_3_2320

Ducros 1992 espèces proies des chimpanzés et baboins

Ducros 1992 primates consommant des mammifères

Insectivory by gorillas
Harcourt & Harcourt, 1984
https://www.karger.com/Article/PDF/156184

L’alimentation protéique du Chimpanzé dans son environnement forestier naturel.
Claude Marcel Hladik, Gérard Viroben, 1974
https://hal.archives-ouvertes.fr/file/index/docid/561721/filename/Alimentation_chimp.PDF

Des variations de longueur de l’intestin
Block, 1904
https://www.persee.fr/doc/bmsap_0037-8984_1904_num_5_1_7864