deletions | additions       diff --git a/Intelligent Life.tex b/Intelligent Life.tex  index f0dbce2..784621b 100644  --- a/Intelligent Life.tex  +++ b/Intelligent Life.tex 
...
The next factor in the Drake equation measures the \textbf{probability of life evolving into "intelligent life".} Intelligence gives a clear evolutionary advantage and therefore it might represents a common pathway of life. Broadly speaking on Earth intelligent life has appeared at least a couple of times (\href{http://en.wikipedia.org/wiki/Cetacean_intelligence}{cetacean intelligence}). However we need to consider that the transition from simple microbial life to complex animals was a very long process. On Earth it took more than 3 billion years for life to evolve from single-celled bacteria to Homo sapiens. Therefore the same reasoning used for estimating $f_l$ might argues for a small value, $f_i<<1$, but value of $f_i$, though  it is very hard to come up with a precise number. It seems plausible that $f_i<<1$, so life is widespread but intelligent life is rare.  Note that this perspective is quite different from the very optimistic view of Frank Drake, who argued that life is very likely to evolve into intelligent life, or that $f_i \sim 1$. To communicate with other intelligent life, a civilization has to develop 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. $f_c = 1$