The Internal, External and Extended Microbiomes of Hominins

Abstract

The social structure of primates has recently been shown to influence the composition of their microbiomes. What is less clear is how primate microbiomes might in turn influence their social behavior, either in general or with particular reference to hominins. Here we use a comparative approach to understand how microbiomes of hominins have, or might have, changed since the last common ancestor (LCA) of chimpanzees and humans, roughly six million years ago. We focus on microbiomes associated with social evolution, namely those hosted or influenced by stomachs, intestines, armpits, and food fermentation. In doing so, we highlight the potential influence of microbiomes in hominin evolution while also offering a series of hypotheses and questions with regard to evolution of human stomach acidity, the factors structuring gut microbiomes, the functional consequences of changes in armpit ecology, and whether Homo erectus was engaged in fermentation. We conclude by briefly considering the possibility that hominin social behavior was influenced by prosocial microbes whose fitness was favored by social interactions among individual hominins.

History and Domestication of Saccharomyces cerevisiae in Bread Baking

“…However, it is likely that organized reliance on organisms for fermentation is far older. Amato and colleagues, for example, have recently argued that early hominins likely fermented fruits using yeasts, as early as a million years ago ( Dunn et al, 2020 ). In this context, we suspect that the reliance on yeast for grain fermentation, including that associated with bread making, is much older than current dates based on archaeological samples.…”

Cultures of Fermentation: Living with Microbes

“…In contrast, among humans today, nearly all consumed fermented foods are purposely produced through either spontaneous or selective fermentation, and consumption of fermented foods is a generalized trait shared by most humans, albeit with cultural variation. Studies on taste perception and aversion, moreover, suggest that humans are distinct from most other primates in having a strong preference for the sour flavor of acids produced by fermentation (Dunn et al 2020). Humans clearly have a special relationship with ferments.…”

“…And, when ingested, fermenting microbes act as probiotics and additionally supply prebiotics to the gut microbiome. As such, Dunn argues that fermented foods act as an extended microbiome, an externalization and functional expansion of the metabolic processes carried out within our own bodies (Dunn et al 2020). When fermented foods became a regular component of human diets, however, remains uncertain (Dominy 2015), and it is not clear whether functionalist arguments that human ancestors could metabolize the products of fermented foods (Carrigan et al 2015;Dominy 2004) are sufficient evidence that they did (Milton 2004).…”

Endocrine cross‐talk between the gut microbiome and glial cells in development and disease

“…During mammalian evolution, the gut microbiome co-evolved to adapt to and coexist in a symbiotic relationship to regulate mammalian development and behaviour. 1 This has led to recognition of the microbiome-gut-brain axis. The gut microbiome and the brain communicate mainly via the vagus nerve and blood-borne microbial metabolites.…”

“…The human intestine contains a complex microbial community referred to as the gut microbiome. During mammalian evolution, the gut microbiome co‐evolved to adapt to and coexist in a symbiotic relationship to regulate mammalian development and behaviour 1 . This has led to recognition of the microbiome‐gut‐brain axis.…”