THE FAMILIAR AND PUZZLING WORLD OF ORGANISMS

In the introductory chapter, I said that organisms were paradigms both of living agents and of biological natural kinds. They appear ubiquitously across hierarchically ordered lists of biological entities and are familiar both to common sense and within the biological sciences. When we think about the biological world, organisms leap out at us immediately as the agents of life to such an extent that it is sometimes difficult to envisage life without organisms.

So everybody knows what organisms are. Given all of this, it may seem unwise for me to waste all of our time with a chapter on the question “What is an organism?” But even if organisms are obvious, almost inevitable denizens of our thinking about life, the concept of an organism stands in need of some elucidation. Consider the following three examples and questions that naturally arise about them.

In the early 1990s, a team of biologists led by Myron Smith reported in the journal Nature that they had found that fungus samples of the species Armillaria bulbosa taken over a region of fifteen hectares in Michigan's Upper Peninsula had a very high level of genetic similarity. They used their data to argue that these samples constitute parts of one gigantic fungus. Estimating that the biomass of the fungus, most of which was located underground and connected by rhizomorphs, was more than ten tons, and that the fungus was over 1,500 years old, they concluded their paper by saying that “members of the fungal kingdom should now be recognized as among the oldest and largest organisms on earth.”