deletions | additions       diff --git a/Intelligent Life.tex b/Intelligent Life.tex  index b12d76e..788c10d 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 may represent 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 argue  for a small value of $f_i$, though it is very hard to come up with a precise number. It seems plausible that $f_i<<1$, meaning that even if life is widespread, intelligent life might be very 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 a large fraction of intelligent lifeforms might eventually evolve towards a technological, communicative form.