John L. Ingraham - Kin: How We Came to Know Our Microbe Relatives

Were fascinated by our origins. The worlds vastly disparate religions share a common fascination with our and all lifes beginnings. Both DNA testing and internet databases are available to search for ones relations, ancestors, and ethnic origins. We and our ancestors have often seemed driven to know where we came from as individuals and as a species. Relatively recently, some of these most primal questions have been definitively answered: we have come to discover our collective origins, at least in broad outline, and to recognize our remarkable kinship to microbes.

Modern biology has constructed a new scientific origin tale with an impact equivalent to cosmologys big bang theory. The components are the newly established relationships among living things. Assembled, they make a clear and dramatic statement: we are all kin. From the smallest bacterium to the largest blue whale, we are all fellow members of the same inclusive family of life. We are connected by common and traceable inheritance that leads back to this familys microbial beginnings.

Since Charles Darwin, biologists have suspected that we descended through a single, branching pathway of life, but now its been unequivocally established. As we might anticipate, parts of the pathway have some unusual twists and turns. This common legacy of living things, which has been established with certainty only during the past forty-odd years, has gone largely unnoticed, or at least underappreciated, by those of us who arent biologists. We still dont know where were going and can only guess about how it all began, but now we do know with certainty where we and our fellow living creatures came from; to whom we are related and how closely.

This research establishes much more than lifes singularity. It displays the relative closeness of the relationships among various organisms as well as their genetic interconnections. It tells how we acquired individual components of our cells: how our proteins evolved by assembling component parts from disparate sources, and how some of our essential cellular functions were acquired directly from microbes.

The new origin tale reminds us, as wed already learned from traditional studies and from observing nature, that were most closely related to other animals. As W. Ford Doolittle noted, before this achievement, we would still find it easy to tell birds from bees, or distinguish any bird or bee from broccoli, brewers yeast, or bacteria. But we would have no strong basis for deciding as we have that all birds and bees are closer kin to yeast than to broccoli. Now we know that our relationship extends to all of them. We share common ancestors with plants. Most surprisingly, perhaps, new discoveries not only firmly establish that we are descendants of microbes, they explain our connections to them. The most basic, life-sustaining activities of the cells comprising our bodies, including those that enable us to digest our food and derive metabolic energy from it, evolved in microbes. More fundamentally, we store our life instructions and pass them on to our progeny along the route pioneered by microbes. We werent the venues for developing these fundamental bases of our being; we acquired them through inheritance from our distant microbial relatives.

Perhaps an even greater impact of these studies is the revelation that such things are knowable, that a question of such profundity may be answered by ordinary laboratory experiments, some seemingly mundane and tedious. Might other biological conundrums be similarly penetrable? Certainly the discovery of a totally new class of organism, the archaea, in 1977 came as a major surprise. These newcomers (to us) are unique among living things, as different genetically, biochemically, and evolutionarily from other microbes as they are from us. The novelty of their discovery is unparalleled in the history of modern biologyequivalent only to Anton van Leeuwenhoeks amazement upon discovering a world of microorganisms on the glass beneath his homemade, handheld microscope in the seventeenth century.