r*

In the moments before beginning his informal gathering of searchers for extraterrestrial intelligence in late November 1961, host astronomer Frank Drake, who had convened the conference to promote his programme Project Ozma that monitored a pair of nearby, sun-like stars for radio signals, dashed off his probabilistic conjecture, the eponymous equation proposed to estimate the number of communicative civilisations in the galaxy.  While subject to criticism for the speculative and unknowable nature of many of the factors, it is nonetheless a useful heuristic from the individual whom would go on to champion the conversion of the Arecibo site to a radio telescope and entrench SETI in the popular imagination: Whereas N is the number of alien civilisations within our current light cone derived from the rate of stellar formation multipled by the fraction hosting exoplanets, by the average in the Goldie Locks Zone, times the fraction that develop and sustain life long enough to develop a technology detectable by other distant civilisations and finally the length of time such civilisations stick around.  Through research and observation, the incidence of some factors can be arrived at, but other parameters are very much androcentric and do not account for colonization and the rise and fall of successive dominant life forms.