deletions | additions       diff --git a/Intelligent Life.tex b/Intelligent Life.tex  index e820ecf..458253d 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".} life"}.  Intelligence gives a clear evolutionary advantage and therefore it might represents may represent  a common pathway of life. Broadly speaking 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 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. \begin{quote}  $f_c \sim 1$ \end{quote}  Putting these factors into the Drake equation above we get   \begin{quote}  $N \approx \, \frac{1}{4}\, f_i \, L $.   \end{quote}  This states that the number of communicative civilizations in our Galaxy is just the product of the chance of emergence of intelligent life times the average lifetime of a civilization's communicative phase. It seems hard to be able to put strong theoretical constraints on both these factors. However However,  one can turn the problem around, and in the next and last final  post of this series I will show how the current search for radio signals from extraterrestrial intelligence can be used to put some important constrains constraints  on the two factors $f_i$ and $L$, and how these informations this information  can be used to makesome  bold predictions about the future of humankind. %Note this is basically the same result that Frank Drake obtained in 1961! The difference is that this has been %obtained only making assumptions on the factors $f_i$,$f_l$ and $f_c$, since the other terms in the equation %are now established.