I often talk to people who are convinced that that aliens are visiting our planet. They believe in UFOs.  Having thought about it, I've concluded that it's highly unlikely that we're being visited by aliens.

It's not that I don't think there is intelligent life in the universe. Space is big. Very big. And there are trillions of worlds in this universe and so statistically it seems pretty likely there are intelligent beings on other planets. But how close would these beings be?  One of the great misconceptions about evolution is that intelligent life, such as humans, is inevitable.  It's not. In fact, consider this: In the something like 3 billion years that the Earth has existed, humans are the only ecomorph that could have built a civilization.

Let's talk about ecomorphs first.  An ecomorph is a general bodily shape. Pick a time in history and odds are the same ecomorphs will appear.  Eliminate mammals and reptiles from a habitat and eventually you will end up with birds that will fill all the ecomorphs. Hard to believe? It's happened countless times.  New Zealand was once totally dominated by birds who filled in all the common ecomorphs. Mammals and reptiles failed to colonize New Zealand because of its relative isolation. Over time, these birds evolved to form the common ecomorphs (flying predators, land based predators, land based herbivores, etc.).  We think of birds as feathered flying things because that is the one ecomorph that this particular class of animal has successfully dominated.  But take away the mammals and reptiles from say North America, give some time, and you'll end up with herds of large animals that are essentially flightless birds.

Some ecomorphs show up again and again. Vultures, for instance, are on every continent even though genetically they have nothing in common. They are simply two types of birds that evolved to fill that niche (the flying carrion eater). It's really the niche that determines the ecomorph.

Which brings us back to our friends the humans. Humans have a few very unusual traits amongst animals. Traits that are all required in order to have built civilization (as we know it anyway). The first trait is obvious - large brains. Brains, however, are not very advantageous until they get to a certain point. They consume a great deal of energy and thus require a lot of food to power. That energy has to deliver something pretty useful in exchange or the species quickly becomes extinct. A large brain on its own isn't enough. Dolphins have reasonably large brains and they're not likely to be colonizing space any time soon. This brings us to the second particularly unusual trait amongst humans - our arms (not hands, we'll get to that). Consider every animal you can think of in the history of the world. How many can perform the simple duty of reaching back and touching their own backs?  In the 3+ billion years that life of some sort has existed on this planet, only primates have evolved to be able to do that. What a fantastical coincidence that primates happened to be blessed not just with this truly unique ability but also have large brains? And don't kid yourself, the two did not evolve together. These two things were happy coincidence that led to the final and most important and unique trait for humans.

The last and most important trait that is unique to humans and yet required to build a civilization is our hands.  Once again, out of the billions of species of animals that have existed on this planet, only humans have hands this dexterous. Not even our primate cousins can do as much with their hands as we can. Forget our huge brains for a second. Our hands on their own are truly unique. We can make things with our hands. Of course, making things with our hands would mean nothing without our large brains. But having one does not necessarily mean the other would evolve.  Give a gazelle a large brain and it's still lion food. Give it our hands and it's still going to get chowed down too.

In other words, humans aren't just unique for our large brains. There are 3 different wholly unique aspects to humans that in all the history of our planet never evolved as an ecomorph before. The dinosaurs roamed the earth from 300 million years ago to 65 million years ago. Did any of them have the ability to reach behind their heads? Did any of them have hands that could grasp and manipulate anything? Did any of them have particularly large brains? No. The closest you get are the raptors who are probably only as smart as a mid level mammal (despite what Jurassic Park may make you think). And they weren't scratching their backs with their claws.

And consider the unlikely ness that mammals are the dominate species at all. If it weren't for a meteor hitting the earth precisely 65 million years ago there's nothing to say that dinosaurs wouldn't still be masters of this planet and our ancestors still being small rodents on the edge of extinction.

So what does this have to do with aliens? A lot actually. You see, while we can debate all day whether life may exist elsewhere in this galaxy or universe, the real question comes down to what are the odds of intelligent life existing. Even if you manage to get life going in the first place somehow, and even if they somehow manage some sort of sexual reproduction or equivalent, you aren't anywhere close to having intelligent life. And I suspect just getting complex life requires a number of exceedingly unlikely events to occur. And it seems pretty obvious that getting to intelligent life requires a set of remarkable coincidences that are so unique and so unlikely that it's not something we're likely to find on even 1 out of a billion planets that already have complex life.

Which doesn't rule out intelligent life. Like I said, space is big. But that's also the problem. Space is very very big. And so if there is other intelligent life out there, the odds are that it is very very far away.

And if it is really that far, it just doesn't seem likely that they would use their trans-galactic-warp engines to buzz hicks on farms like a bunch of rowdy teens taking out dad's car.  I think the more likely scenario is that intelligent life is simply too far away for us to realistically ever come in contact with. Then again, I could be wrong. And if so, I'll be the first to welcome our hyper-intelligent space ant overlords.