Ah, well consider the following.  Scientists can reverse engineer cell developement to the point where they have determined exactly how cells formed on the primordial Earth.  The one thing they can not account for is how DNA was created on Earth.  Well it turns out that viruses are so small and light that brownian motion of air molecules and vertical wind currents can lift viruses up to the edge of space, at which point the solar wind blows them off into deep spaces.  Therefore there are viruses drifting through space which will eventually reach other planets.   Now consider that the universe began almost nine billion years before our sun.  Therefore there are also some solar systems that are at least 8 billion years older than our solar system.  It is possible for viruses to drift across entire galaxies and inseminate all the planets in the galaxy by the time the Earth cooled enough to support life, and likely also possible to have drifted across the vast reaches of intergalactic space and colonize other galaxies, where the virus would have invaded the proto-cells and allowed for life as we know it to begin.  So, DNA came from space !   Therefore it is likely that much life in the galaxy originated from similar viruses that  spread around and therefore a lot of life in the galaxy has some basic similarities to ours.  We can see that all complex life that evolved from this original DNA that landed on Earth has some great commonalities.  There is always a head at one end which contains sensory organs and feeding apparatus and the eliminator at the other end.  All the life is bilateral, having a right and left sides which are more or less a mirror image of each other.  All animal life has some form of locomotion which is located on the body, behind the head, and the more advanced forms of life have as few limbs as needed to function, as a form of evolutionary efficiency.  One thing to keep in mind is that a carrot has DNA with a seventy percent similarity to human DNA.   Now since much life in the galaxy probably stems from a similar original viral form of DNA then it is reasonable to assume that they would evolve along similar lines, and even if the original DNA was different it appears that the rules of evolution, which are based on maximizing efficiency, will lead to similar results, which is a head with two eyes and two ears and then a torso which normally has four legs, or two legs and two other appendages which could belike arms or wings. This will eventually lead to some beings that walk upright on two legs and have hands with which to manipulate things, which even existed in some dinosaurs.  Eventually evolution will also lead to higher intelligence, just as it has on Earth, in several animal species.   Now also consider that due to all this some intelligent life will have around an eight billion year head start on the human race.  If you consider how much our technoilogy has advanced in only one hundred years then you can see how some technological beings with an eight billion year head start can easily have invented space travel eight billion years ago and spread across the galaxy, and the chance is vanishingly small that it did not happen.  These people would also have the ability to do genetic engineering.   Due to all this it is likely that humanoids, and in fact humans themselves, exist throughout the galaxy.   I made all the conclusions up.  I'm not like Drew, who has to quote some academic losers in order to try to prove some idiotic concept.  Let it appeal to you reasoning instead.