Thomas Kuhn stated that the vast majority of scientific research is conducted within the confines of a paradigm. Paradigms include not only theories but also methods, instruments, concrete examples, sanctioned texts, and, most importantly for our purposes, subsidiary assumptions. They are invaluable tools for scientific research, facilitating the construction of hypotheses, design of experiments, and interpretation of results. According to Kuhn, however, paradigms may also hinder the exploration of nature, blinding researchers to important possibilities by discouraging certain avenues of investigation and biasing the ways in which data are interpreted. As a consequence, important scientific discoveries may be delayed for years.
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| All life on Earth (that we know of) has a similar DNA-based chemistry Credit: NASA |
Kuhn used examples from astronomy to illustrate how paradigms can blind scientists to new discoveries. Similar cases can be found in biology, such as the discovery of Archaea, a new variety of familiar microbial life that revolutionized biological taxonomy. In hindsight, it is clear that there were signs that some prokaryotes are fundamentally different from others, despite their remarkable similarities in cellmorphology. But because biologists were working under the prokaryote-eukaryote paradigm, which used cellular morphology as the guiding principle for understanding taxonomic relations, these signs went unrecognized. Indeed, what are now understood to be telling chemical differences in the membranes of Archaea and Eubacteria were interpreted as mere adaptations of familiar “bacteria” to extreme environments. Microbiologists had unwittingly stumbled upon a new kind of microbe, but failed to recognize it because they were working under the prokaryote-eukaryote paradigm, which denied that such microorganisms exist.
The lesson should be clear. Because microbiologists are working under a paradigm that says there is only one form of life on Earth today, it is unlikely that they would recognize the significance of traces of an alternative form of microbial life even if they encountered them.
While we don’t know how different life could be from life as we know it, there are good reasons for thinking that life on Earth could have been at least modestly different in its molecular architecture and building blocks. A dedicated search for shadow microbes ought to be seriously considered. The obvious place to begin is with known puzzling phenomena, such as desert varnish, that are difficult to explain in terms of familiar life and yet also difficult to explain in terms of abiotic processes.
The discovery of a shadow microbial biosphere would be philosophically and scientifically important. It is clear that familiar Earth life has a common origin, and hence represents a single example of life. Logically speaking, one cannot generalize on the basis of a single example. If we are to achieve a satisfactory understanding of the general nature of life, we need examples of unfamiliar forms of life.
