As far as we know, all complex organisms have an accompanying microbiome of commensurate species, even the most basic ones like marine sponges [1]. Plants nurtu

As far as we know, all complex organisms have an accompanying microbiome of commensurate species, even the most basic ones like marine sponges [1]. Plants nurture these symbionts in their roots while animals do it in their digestive tracts (mostly, both have surface microbes too that do various things too). [1] https://www.nature.com/articles/s41396-020-0591-9 https://www.nature.com/articles/s41396-020-0591-9