How will Aliens look if they are out there?
Are we alone? Who has not asked himself that question. With a universe so big around us (as far as we know it is endless so big doesn't even begin to describe it) there must be about an infinite amount of planets. This means that even when the chance of alien life is really small, it must exist. So lets assume for now that alien life exist, how far away are they? And maybe even more important, will we ever see them? All of these questions are unanswerable as far as I know. Another question that rises when assuming that aliens have to exist is what will they look like? Now this question may sound as unanswerable as the other questions, but maybe this one is easier to discuss. Some major groups can be made from looking at science and movies, I will address those. After that I will try to cover what restrictions lifeforms may have and how that affects the alien appearance. So if you have ever wondered what aliens would look like, read on!
The advanced human appearance:
A lot of movies have aliens attacking earth or when we're lucky come to warn us for some kind of disaster. These movies show us aliens in the flesh and our image of aliens is affacted by these movies. But do these moviemakers give us a realistic image of an alien? The alien look that is used the most is a pale naked beeing with a big head and big dark eyes. This image is derived from humans, some scientists think that if we keep reproducing long enough humans will all begin to look more like each other. Unneccessary features like hair will disappear, the big head comes from us using more of our brain (we are at 40% of our capacity now) and from the fact the brain has always grown during evolution. If we were compared to our early ancestors like the first Homosapiens erectus our skull has a different form because our brains grew bigger. Often these aliens do not have a mouth, this is because it is believed that communicating will be done via telepathy.
Is this alien look realistic? It is possible, but for aliens to get looks like this (some kind of very advanced humans) they would have to live on a planet that is very similar to ours. They have to have looked like us at some point and that isn't very likely. We are adapted to life on earth and of course to evolve life on a planet it probably has to be at least something like our planet, but the chance at a second earth is very slim. So the actual chance of aliens looking like this are rather small I'm afraid.
The aggressive insect appearance:
Next to the advanced human appearance, the aggressive insect appearance is one that is found regularly in modern entertainment. Often the alien race travels around the universe and tries to exhaust the resources of the planets which they encounter like an insect plague. Is this appearance a realistic one? I would say no, first of all it seems unlikely that these kinds of aggressive insects are extremely intelligent as well. Just looking at humans it is clear that the most intelligent among us are not aggressive and usually the more aggressive among us are not the scientists. So agressiveness and high inteligence do not come in one package. And it requires some kind of high intelligence to be able to design technology which makes a race able to travel large distances through space. Secondly, what do all those insect do on their home planet/ship if they cannot fight anything? I don't really see them playing a friendly game of chess or baking cakes. They have huge advanced ships yet they act like mindless insects. On Earth giant insect cannot even exist because of the way they breathe. Insect use small tubes in their chitin armorplates in which the air will flow, and by diffusion the oxygen will reach their cells. Diffusion of air can only go through a couple of layers of cells, so if insect don't evolve lungs they will have to stay this small because becoming bigger will mean thicker cell layers and no oxygen to reach it. So they aliens would have insect appearance but some kind of mammal intestines, it would be unlikely for a creature to evolve this way.
So is the aggressive insect appearance a realistic one? No, the scenario of Earth being attacked by giant insect from outer space is very unlikely. It works great in the movies but has to much problems in reality to be real.
So what will aliens look like?
First of all lets discuss the major form of the aliens starting with how big they will be. On our planet we have huge whales and elephants but also lots of smaller creatures. Humans are somewhere in the middle of all animals when looking at size alone. Will it be possible for intelligent life to be very large? Theoretically this would be possible, but being a lot smaller is possible as well. Being very much smaller then we are would come with some problems regarding to the laws of physics that apply on our planet and would be very unlikely. So as far as size goes it is difficult to say what it will be but it is likely that they would be about the same size as us.
Would they be walking on 2, 4 or even more legs? When we look at our planet humankind is not the only bipedal species that ever existed on earth. Take for example the Tyrannosaurus rex and many other dinosaur species. Almost all larger lifeforms use two or four legs for transport, and nowadays almost all animals have four legs because of the advantage in speed and agility (six legs would make them slower and less agile). So why did we start walking around on two legs? That is only because we started using our hands for making and using tools. So looking at evolution over all the millions of years two or four legs would be the most logical. To be able to build structures and even spaceships the aliens are going to need something like our hands, because building usually requires tools. So aliens will have arms and hands and will probably walk around on two or four legs.
The shape and appearance of the aliens will be influenced by the planet they are from. If they would live on a hostile planet with high temperatures or lots of radiation their skin or would look different or they would need scales or some kind of shell against the high energy particles in the atmosphere. So the size and manner of walking would be like us humans or some kind of animal, but the color or kind of skin/shell is really hard to predict. We know that organisms sometimes are able to live under extreme conditions (Waterbears for example can survive in boiling water) and that makes it even harder to predict what kind of planet the aliens would live on. If they could cope with conditions that we cannot they will look very different from us. On Earth carbon is the main building block of all organisms, it could be the other planet has another element as the main building block, making aliens have an amazing appearance. So many things could be different on their home planet compared to Earth which will influence their appearance.
The shape of the aliens would depend a lot on the characteristics of their home planet. It could be some kind of Earth but it could just as well be completely different. That makes it very hard to predict the appearance of alien life. Some predictions can be made however, they will have arms and hands if they build spaceships and they will probably have two or four legs. The advanced human appearance is the most likely from all of the movies but they will have to have a homeplanet that is very similar to ours. But even if their homeplanet is like ours it doesný mean they will have to look like us. What if the dinosaurs were never extinguished and they would have become intelligent in a couple hundred million years? Then some kind of reptile humanoids would have walked the earth.... The appearance of aliens will unfortunatily always remain a mystery until we actually meet them.