PERSPECTIVES H

uman bodies house trillions of sym-biotic microorganisms. The genes in this human microbiome outnum-ber human genes by 100 to 1, and their study is providing profound insights into human health. But humans are not the only ani-mals with microbiomes, and microbiomes do not just impact health. Recent research is revealing surprising roles for microbiomes in shaping behaviors across many animal taxa—shedding light on how behaviors from diet to social interactions affect the compo-sition of host-associated microbial commu-nities ( 1, 2), and how microbes in turn infl u-ence host behavior in dramatic ways ( 2 – 6)