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Once life emerges on a planet, what's The next factor in  the \textbf{probability that will evolve into intelligent life?} Depending on Drake equation measures  the exact definition \textbf{probability  of intelligence, life evolving into "intelligent life".} Broadly speaking,  on Earth it intelligent life  has appearedprobably  at least a couple of times (\href{http://en.wikipedia.org/wiki/Cetacean_intelligence}{cetacean intelligence}). Intelligencealso  gives a clear evolutionary advantage and therefore  it might represents a common pathway of life. On life, however we need to remember that  the other hand, following transition from simple lifeforms (microbial life) to animals is a long, complex process. If we follow  the same reasoning used for estimating  $f_l$, the fact we find out  that it took more than 3 billion years for life to evolve from single-celled bacteria to Homo sapiens sapiens. This  might argue for a small value of $f_i$. Overall this term is very uncertain; using Frank Drake optimistic guess one has $f_i = 1$. To communicate with other intelligent life a civilization has to develope some sort of technology. If again we consider Earth's case, this happened for humans but not, for example, for dolphins. The factor \textbf{$f_c$ measures the fraction of civilizations that develop communicative technology}. As intelligence and curiosity seem to go hand-in-hand, it seems conceivable that all intelligent lifeforms might eventually evolve towards a technological, communicative form. $f_c = 1$