My reasoning for the statement that 'intelligent aliens are unlikely' is based on a number of points which I am going to discuss. This is all just a theory of course and a product of my own cognition, but bare with me and let me know what you think.

PREHISTORIC LIFE

The Dinosaurs lived for over 135 million years yet never evolved into anything more than mindless beasts. We have fossils but there's no evidence of them living in buildings or utilizing advanced technology or even basic technology for that matter.

135 million years. We have been around for around 200 thousand years, or so they say. Which is a fraction of what the Dinosaurs inhabited the planet for. That's approximately 0.145% of the time in which they served. So nothing sparked their evolution? Well it did! And that was interaction with each other. Though the evolution they under went never overcame our own.

SURVIVAL OF THE BEST SUITED

The dinosaur kingdom as you had probably guessed, evolved in the same way in which our animal kingdom evolves today.

Evolution is fueled by predator/prey interactions. Prey evolves random flaw which increases Its defense and passes the flaw on. Predator evolves flaw which increases its offense and passes it on. This is the basis of evolution, so what the heck did we have to fight against to evolve into this intelligent being?

Well my answer is a race of species that we had to compete against. That's the only answer is it not? The rival would make a leap of advancement and we would have to also or face extinction. Simple as that. That is until the point of advanced intelligence. Could both species have evolved that or did one have the flaw and the other stole it through reproduction? Or was the intelligence factor just a matter of locked potential.

OUTSIDE INFLUENCE

The above I'm more inclined to believe, but some may argue an influence from an outside source. Which I'm not saying is impossible. If God does indeed exist, then God may well have changed us.

A virus may have infected us and mutated our DNA, strange things may happen.

Or Intelligent Aliens, may have done what God did not. But the fact is I believe these to be unlikely, especially the latter. As I've stated before, all the animals that have lived among us to this very day and the dinosaurs that came before us. Not one of them became or have become intelligent beings, simply because they lack a supreme rival. Ok they have predator and prey influence but not the rival they need to challenge them. Perhaps they also lack the underlying ability anyway. Maybe we did have the mind, but we needed to be challenged into it.

RIVALRY AND THE BATTLE OF THE RACES

I believe our evolutionary phase is over now, but only in the major bodily changes sense of the word. Look around, we only differ now from the past in the clothing we wear. Ok on the whole a bit taller maybe, but we consume different things now, somethings we perhaps shouldn't even be.

It's the evolution of the mind that continues. We continue to fight and strive, to Excel in moving the world forward, technologically, and scientifically, etc.

But what pushes us? Well what has pushed us since we can remember? Rivals!

These rivals are different races, It's why countries have gone to war, It's why we fight to be the world power. Why else do countries have borders? If you believe in the moon landings and the Russian and American space race, what do you think it was for? Fun? The space race was about power, about who was smarter, about which race could achieve greatness through the evolutionary mind.

So it is individual races that fuel our current will to achieve the unthinkable. We push each other to further our mind and evolve our understanding of everything.

AN OUTSIDE RIVAL

So what if our Alien friends had the same potential and a rival to push them? It's unlikely, but maybe It's just what we need.

Imagine this new rival from out of space, challenging our right to this world. That will be the day when Humans stand together, for the first time as a collective species, every man an equal in the others eyes. Ready to take on our new rival, and to push the boundries of our minds as we are forced to evolve or die.

You are not taking into account the incomprehensible size of our universe. Probability favors the existence of other intelligent/sentient beings due the countless billions of planetary bodies in our universe.

Who knows....no matter how impossible it seems you could be right.

I know not, therefore aliens...

I understand what you mean. But in some of the ways you talk about Rivals is the way someone would talk about Enemies. Now i do get your point really and just because you have a Rival doesnt mean they have to be your Enemy. Everything has a challenge not just living things. If you work as a team then youll do things much faster. If Enemies became friends and worked together their is no doubt that we would advance much more faster than actually killing eachother