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> Bacteria play a role in every activity in the body, as the microbiome is studied and the influences the bacteria create is recognized:
> 
> https://www.quantamagazine.org/should-evolution-treat-our-microbes-as-part-of-us-20181120/
> 
> “'We’ve underestimated the potential contribution of microbes to traits we’ve been studying for decades or centuries,” said Kevin Theis, a microbiologist at Wayne State University who studies the paste-making microbes of the hyena. “If the genes for these important traits are actually in the microbiome and not the animal itself, then we need to take a systems-level approach and look at the host-microbe system as a whole.”
> 
> "Look closely enough at any plant or animal and you will discover a riot of bacteria, fungi and viruses forming a complex and interconnected ecosystem. A recent explosion of research reveals how deeply we rely on our microbial patterns to keep our bodies functioning, raising profound questions about what it means to be an individual.
> 
> ***
> 
> "Some biologists are calling for a radical upgrade of evolutionary theory, arguing that prevailing ideas, developed from the study of bigger, more easily understood organisms, don’t fit nicely into this new world. Others contend that existing theory just needs to be applied more carefully. All agree that the micro and macro worlds are inescapably interdependent, and that biologists must explore the frontier of their interconnections.
> 
> ***
> 
> "Holobionts and hologenomes are “incontrovertible realities of nature,” wrote Theis and his colleagues in the journal mSystems. Hologenomes contain vastly more genes than the host genome alone, and since at least a fraction of the microbial genes have significant bearing on the survival and reproduction of the host, we need to consider the hologenome as a possible unit of selection if we want to understand the evolution of the holobiont.
> 
> ***
> 
> "Proponents of this hologenomic concept of evolution argue that if there is a fidelity across generations between hosts and microbes, then the holobiont embodies a coming together of numerous, disparate evolutionary lineages into a singular being, a coalition of many that contributes to the functional integrity of the whole. Only when considering the holobiont as a single entity capable of being shaped as a unit by natural selection can we make sense of its complexities.
> 
> ***
> 
> "Typically, human babies not born by cesarean section acquire their mother’s vaginal microbes en route to the outside world. Mom’s microbes also rub off on a baby through close contact and breastfeeding. Although eventually the microbial community changes as the child moves more freely through the world, these early microbes play an outsize role in immune system development.
> 
> ***
> 
> "Strassmann argues that focusing solely on what’s happening in the holobiont misses much of the microbes’ story. Many host-associated microbes spend significant chunks of their lives outside their host, in an environment where they’re subject to very different selection pressures. The holobiont idea, she says, puts blinders on our understanding of the evolution of these microbes, focusing attention on the host environment and neglecting other habitats that could shape a microbe’s character.
> 
> "Critics of holobiont-centered theories are not discounting the importance of studying the interconnections between microbes and hosts, but they think the holobiont framework is almost always misleading. They envision the holobiont as an ecological community, not an evolutionary individual. The knowledge that symbiotic relationships with microbes are important “doesn’t mean we have to completely forget what we know about how evolution and natural selection operate,” Strassmann said."
> 
> Comment: the article continues with debate about the meaning of this approach as if offers a new avenue to thinking about evolution. What occurs to me is we can see a new role for bacteria which have persisted since the beginning of life  and perhaps this is the reason why they have remained so active in the process of evolving. They take new roles to play at all  stages. They create immediate adaptations, for example, in digestion, but it is certainly obvious they do not design  giant changes.