I have never made a big secret of my passion for microbiota biology. The interaction between microbial communities and host organism is definitely one of the best topics to take stock of  the amazing complexity of biological systems. In fact, I have already discussed about some possible applications for theoretical biology in this field, and introduced a couple of bioinformatics methods aimed at metagenomics analyses. Today, I return to this topic to report a brand- new amazing paper on Cell, authored by Julia K. Goodrich and co. from the Ithaca University (New York).

How are human genetics and microbiome composition interlinked? This study proposes a strong genetic determination in the abundance of many microbial taxa in human gut microbiota, after an investigation on more than 1,000 fecal samples from 416 twin pairs (homo- and heterozygotes) living in the UK. Intriguingly, “the most heritable taxon, the family Christensenellaceae, formed a co-occurrence network with other heritable Bacteria and with methanogenic Archaea”, and data prove its strong role in the onset of obesity, suggesting new possible therapeutic applications.

As I skip a well- detailed discussion, letting you insight this paper on Cell’s website, I limit to rattle off a couple of considerations on the *theoretical side*. The interplay between gut microbiota and host genome, even if strongly supported in this work, is not a big novelty. Under an evolutionary point of view, the importance of symbiosis in organisms’ life and adaptation, gave rise, in 2008, to the very debated “hologenome theory of evolution“, that propose the “holobiont” (organism + associated microbial communities) as the subject of selection instead of the mere organism.

Actually, I never focus on genomic evolution only, sensing that, if defined as the change of dynamic and replicating complex systems over generations, evolution cannot be properly studied at genomic level only. In host- microbiota interaction, we appreciate a complete mutual dependency between organisms belonging to very different domains. The microbial community behavior, the immune response, the cell-to-cell communication, epigenomic regulation, protein interactions, and the effects of genetic determination found in microbiome studies, indicate a very complex and multi- level process as determinant in any eukaryote- microbial symbiosis. As we get totally aware about the relation between human genetics and microbiome composition, the open questions are still  in which way, and to which extent, host genome can affect microbial communities, and how much the symbiosis influenced adaptation and evolution of higher eukaryotes.

And this explains fairly well why I am so interested in everything about microbioma. Studying the way how microbes live along with animals and plants, makes a perfect framework to tackle questions of general interest in theoretical biology. As in any study, we can recognize an interplay between complex systems at a different organization level, and to understand the evolution, we need to accept complexity as a fact, and try to understand in which extent any level contribute to adaptation and evolution. Though, differently than other fields, I sense that the microbiome constituted a very effective framework to do this.

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