In the light of the principle, a number of other topics deserve renewed attention. Below, four of them are briefly touched: Fermi's question, the anthropic principle, extraterrestrial intelligence and panspermia.
The famous question posed by Enrico Fermi in an informal conversation during a lunch at Los Alamos, in the summer of 1950 [see later account by Eric M. Jones (1985)], became central in the discussion of the existence of extraterrestrial civilizations (e.g., Newman and Sagan 1981). ``-- Where is everybody?'', asked Fermi, talking about extraterrestrial life. The answer to Fermi's question is plain and uninteresting: ``-- They are where they belong to''. Yet they are, states the extraterrestrial life principle.
The anthropic principle (see, for example, Barrow and Tipler 1988), which certainly with justice should be dubbed the masterpiece of human arrogance, is thus irrelevant since the human ecology is but one amongst many.
The search for extraterrestrial intelligence (e.g., the SETI project, see http://seti.planetary.org/) is strengthened by the principle. But an eventual absence of contact with extraterrestrial civilizations should not be confused with their non-existence. Establishing contact with alien populations is not a prerogative of intelligent life but of a given cultural and social characteristic of intelligent life (e.g., mercantilism, in the case of mankind, as a driving force for contact between distinct societies on Earth in the XV and XVI century).
Finally, it is important to remark that the acceptance, or the eventual empirical verification, of the so-called panspermia paradigm (see electronic links to this and related issues in http://www.panspermia.org/ ) makes the extraterrestrial life principle obvious.
Acknowledgment -- I would like to thank Dr. André K.T. Assis for comments and suggestions on a earlier version of the manuscript.
References