Discuss the probability of intelligent life existing elsewhere in the universe.
Space-biology
Fermi Paradox
There could be intelligent life, but that doesn't mean it has evolved or adapted to communicate. Also it's survival of the fittest not the smartest
Drake Equation
References
If there was intelligent life why haven't they contacted us? #
There is a whole equation for estimating the odds of finding life that communicate created by Frank Drake, who helped in founding SETI(Search for Extra-Terrestrial Intelligence)
Another possibility is that the ETI wiped themselves out before they found the need or the curiosity to communicate with other planets
Articles
Chance of other intelligent life existing is 1 in 10,000,000,000,000,000,000,000. Earth is the 1 in 10 Billion Trillion
Adam Frank and Woodruff Sullivan tweaked the equation to not include the length of time alien civilizations lasted.
20% of the known universe is possibly habitable and could have water. This means there is a 20% chance for life to be on one of those planets, that is not necessarily the case with intelligence
Xenomorph 
Humanoid
Humans are narrow in their thinking that aliens would have to be humanoid or bipedal or have a large brain. These characteristics don't define intelligence. Intelligence is "the ability to acquire and apply knowledge and skills". This isn't predominantly defined by the size of the brain or if they have similar adaptations as humans.
click to edit
Entropic Doom
2nd Law Of Thermodynamics
Everything will eventually reach null.
This means that eventually all life will cease to exist because the law states that all energy will disperse and no life will exist once the thermal equilibrium has reached
click to edit
Anthropic Principle
The only reason why we are here and asking these questions is because a certain set of events and things happened that lead to our sapient form
Same applies for aliens there is nothing which should cause them to become sapient and so it would never happen, also certain key events like the wiping out of the dominant species to make way for the new species(Errant Asteroid/Dinosaur Wipeout)