I think it's more an acknowledgement we don't have good ways of mentally modeling the hopes/dreams/feelings of a completely alien life forms. What would we make of a 5-gendered sulfur dioxide-breathing Frisbee-shaped residents of Gloxnor 7?
Think on this. What if the first intelligent alien species we encounter look approximately like us because they claim to have created us and be us and also claim to be the answer to our origin? Methink this will be "The Great Deception".
This post was edited by O-uknow at September 15, 2018 12:30 PM MDT
Different species in similar environments adapt in similar ways to solve the same problems and is why dolphin look somewhat like fish. Blue skinned humanoids are not so far fetched an idea.
We had an example like that not too long ago here on AM. 2 different Australean species (Kangaroos and Emus) that have evolved over a long time while the interior of australia got drier and drier, with food getting more and more scarce. In response the Emus became very good a running and the Kangaroos lucked out with superelastic sinews so they could 'bounce' and make a great many hops 'for the price of one'. 2 very different solutions to the same problem.
But mostly you are right, species that occupy the same ecological niche tend to resemble eachother. It is called Convergent Evolution.
This post was edited by JakobA the unAmerican. at September 15, 2018 12:31 PM MDT