Gut Microbiota Assembly Begins at Birth and Needs to Be Nurtured.

Humans maintain symbiotic relationships with complex microbial communities in their intestinal tracts that are paramount to their host's health and development. Given their importance, it is essential for the host to reliably acquire key members of the gut microbiota and assemble communities that provide benefits during important windows of host development. Epidemiological studies over the last 2 decades have convincingly shown that clinical and nutritional factors that disrupt early-life microbiome assembly predispose humans to infections and chronic noncommunicable diseases. These connections emphasize the importance of understanding host-microbiome assembly on a mechanistic level, the time windows that are most important for host-microbe crosstalk, and the clinical and lifestyle factors that shape and disrupt symbiotic interactions to develop therapeutic and nutritional strategies to prevent noncommunicable diseases. In this article, I will provide an evolutionary and ecological perspective on when and how humans acquire their gut microbiome, the factors that shape the assembly process, and how the process can be disrupted. I will discuss the most important time windows for both microbiome assembly and the microbiome's impact on development of the immune system. Finally, I will discuss how evolutionary and ecological principles inform strategies to support and restore the gut microbiome early in life.