A recent article in the Economist discusses the problem of deciding which geographic locations are actually countries or diplomatic states, and which ones are something less. As the article points out, it's pretty hard to do. You can't just buy some property by the highway, declare your independence from the motherland and enforce a toll at your diplomatic border. There is a process of recognition, etc., and even then there is no clear path to national identity.
The reason people care is that people like having an identity. Identities provide purpose and project meaning. We collect identities like crazy. By the time we're adults, we've accrued and shed and reacquired at least twenty.
Go ahead and count. I'll wait.
A major identity that everyone covets is professional. We grow up anticipating a label of doctor, astronaut, athlete, teacher, star, president and (for the lucky and blessed) scientist.
For many scientists, the specific identity is easily assembled: theoretical physicist, planetary geologist, paleobotanist. But for those sucked into the confluence of certain interdisciplinary fields, things can get tricky. To be in a kingdom and phylum isn't good enough anymore. You need a genus and species. But the taxonomy is fluid, and it's easy to get drowned.
For example, a lot of people get paid to study the brain. Most go through a schooling program with one of these names: psychology, molecular/cell biology, neuroscience, medicine (neurology and psychiatry), or bioengineering. All of these are linguistically distinct and have very different applications and pay grades, but the research itself overlaps to the extent that one project could involve all of those fields at once (like studying A-beta protein aggregates). In brain-machine interface research, all of the brain's biological and medical being suddenly meshes with computational, materials and electrical engineering. There is no one name for someone doing that work, but a number of listings in DSM-IV for those who have multiple identities.
So what is the result? In some cases, it can lead to comically confusing academic divisions. Mostly, it means that the idea of a subfield has become so convoluted and subdivided that it doesn't really matter anymore. A scientist in this situation is a singular being living under a broad tent. They are researchers whose identities are defined by the specific projects of the moment. Those projects could change at any time, thus changing the researcher's identity. The definition of a Renaissance Man becomes redefined. No longer is he the man that does everything; he's the man who can be anything, one thing at a time.
