Recent data suggest that the human body is not such a neatly self-sufficient island after all. It is more like a super-complex ecosystem containing trillions of bacteria and other microorganisms that ...inhabit all our surfaces; skin, mouth, sexual organs, and specially intestines. It has recently become evident that such microbiota, specifically within the gut, can greatly influence many physiological parameters, including cognitive functions, such as learning, memory and decision making processes. Human microbiota is a diverse and dynamic ecosystem, which has evolved in a mutualistic relationship with its host. Ontogenetically, it is vertically inoculated from the mother during birth, established during the first year of life and during lifespan, horizontally transferred among relatives, mates or close community members. This micro-ecosystem serves the host by protecting it against pathogens, metabolizing complex lipids and polysaccharides that otherwise would be inaccessible nutrients, neutralizing drugs and carcinogens, modulating intestinal motility, and making visceral perception possible. It is now evident that the bidirectional signaling between the gastrointestinal tract and the brain, mainly through the vagus nerve, the so called "microbiota-gut-vagus-brain axis," is vital for maintaining homeostasis and it may be also involved in the etiology of several metabolic and mental dysfunctions/disorders. Here we review evidence on the ability of the gut microbiota to communicate with the brain and thus modulate behavior, and also elaborate on the ethological and cultural strategies of human and non-human primates to select, transfer and eliminate microorganisms for selecting the commensal profile.
Animals harbor an extensive, dynamic microbial ecosystem in their gut. Gut microbiota (GM) supposedly modulate various host functions including fecundity, metabolism, immunity, cognition and ...behavior. Starting by analyzing the concept of the holobiont as a unit of selection, we highlight recent findings suggesting an intimate link between GM and animal social behavior. We consider two reciprocal emerging themes: (i) that GM influence host social behavior; and (ii) that social behavior and social structure shape the composition of the GM across individuals. We propose that, throughout a long history of coevolution, GM may have become involved in the modulation of their host's sociality to foster their own transmission, while in turn social organization may have fine-tuned the transmission of beneficial endosymbionts and prevented pathogen infection. We suggest that investigating these reciprocal interactions can advance our understanding of sociality, from healthy and impaired social cognition to the evolution of specific social behaviors and societal structure.
By focusing on the studies of primate behaviour and human neuroscience, we describe how different neurological processes are the base of proximate aspects of social-decision making. We also review ...the fact that distinct aspects of animal behaviour are not under conscious or abstract control and that instead they may be regulated by adaptive 'rules of thumb'. In particular, by describing the microbiota- gut-brain axis we elaborate on suggesting that microbiota has an influence on within-individual aspects of social decision making and in particular facilitating social interactions. Finally, we present comparative evidence of the role of microorganisms as modifiers of aspects of kinship, reproduction and group-members' recognition, suggesting how microbiota also has an influence on between individual aspects of decision making, which are themselves primary aspects of cooperation. In summary, we propose that modern socioeconomic choice theories may still benefit from alternative theoretical frameworks that consider the human being as a complex organism, with intrinsic constraints and capacities product of its evolutionary history, and not just as an exclusively-cognitive decision maker acting independently of its closest partners and commensals: its microbiota.
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