Henry Gee. The Accidental Species: Misunderstandings of Human Evolution. University of Chicago Press, 2013.
Popular media usually portray evolution, particularly human evolution as a sort of ladder of continuous sequence, starting with amoeba and ending with someone like Carl Sagan. Human being want to believe that they are the chosen species, the aim of evolution and that everything and everyone else are just steps on the way or rungs on the ladder. Gee calls this world view “human exceptionalism”
This is not, as Nature editor Henry Gee argues, the case; the tree of life is a vastly complicated bush, no one branch of which is any more important overall than the others. Much of evolution is contingent, including the evolution of human beings. Human evolution is also a bush rather than a ladder leading to us. There is no royal road to greater and greater intelligence, whatever that might actually mean. For much of human history there were several different human groups on earth (whether you should call them species, sub-species or just deep ethnicities is a moot point), and Gee suspects some other hominins (or otherly humans if you prefer) might still have been around even into historical times.
If that is the case, I would suspect they would have to be quite distant relatives, for the genetic evidence of significant interbreeding between our majority ancestors (homo sapiens sapiens, or as they may have been known to other humans “the baby faces”) and groups like the Neanderthals or the mysterious Denisovans, suggests that these were sufficiently like us for there to be little chance for them not to have become largely assimilated into the general population, though there may be isolated groups with much higher than average Neanderthal or other ancestry. If such otherly human groups exist, Gee suspects they will come as a complete surprise and not be anything on cryptozoologists’ wish lists.
Human exceptionalism makes both underestimate and humanise other creatures, and to make it difficult to work out what constitutes intelligence. We might be overrating complex brains, and he suggests that the creatures most mentally similar to us on earth are not chimpanzees but crows! He also argues that our tests of self-awareness, such as the ability to recognise oneself in a mirror show how we privilege human senses such as sight over, say, smell or feel. Similar privileging affects how we envision language, maybe dogs exchange gossip through smell, and how would we know otherwise.
He suggests that if we ever met real aliens they would not be vast cool intelligences, but rather similar to ourselves and crows “liars, cheats, hoodlums and swindlers … also friendly, sociable, sympathetic and above all talkative ...” – Peter Rogerson.