Stop picturing little green men in your mind whenever you talk about aliens because, according to Simon Conway Morris, a leading evolutionary biologist from the University of Cambridge, if aliens exist or we ever encountered them, they would look a lot like humans.
— Sparkonit (from the book The Runes of Evolution)
It has always bothered me that aliens in popular culture media more often than not are humanoid. This never made sense to me. Simon Conway Morris argues that similar conditions would result in a similar fauna on an alien planet, so the alpha predator that would eventually emerge and become sentient would be humanoid.
65 million years ago the Chicxulub asteroid effectively wiped out a majority of the fauna on earth. In particular, the entire dinosaur population did not survive. Scientists speculate that at that time dinosaurs like velociraptors may have been hunting in packs and coordinating their actions. Let’s assume for a minute that the asteroid didn’t hit the earth that day and missed it, and another one didn’t come in the next 65 million years, a quite possible scenario.
Velociraptors would have had millions of years to further hone their hunting skills. Perhaps they might have learned to use tools, first sticks of wood, sharpened at the end, as primitive daggers and later spears. It’s easy to imagine that they would have developed sufficient intelligence to make tools. After all, they had claws with opposable thumbs.
Mammals would never have dominated the earth, and primates may never have evolved superior intelligence. In that world, there would now be the descendants of those tool-making velociraptors as the alpha predators. Sorry, they would look lizard-like, not humanoid.
So, changing one minor detail about our planet’s history by diverting a chance asteroid encounter, a pivotal series of events would not have happened, and the likelihood of humanoid aliens would be minimized.