There is a crow that visits my property and enjoys teasing my cat. He repeatedly alights just outside of Maxi’s lethal range. It seems to me a dangerous game, but he plays it so successfully that half the time my cat doesn’t bother lunging for him anymore. Crows are smart, and not just by bird standards. They have a brain/body mass ratio higher than any great ape other than humans; they rival even us. They recognize themselves in mirrors, thereby demonstrating a level of self-awareness. They make and use tools, such as hooked twigs for snaring larvae from holes in trees. None of that means they are as bright as we are, of course; absolute brain size also counts for something. Yet, they are bright.
High intelligence is rare among animals because it is less useful than one might imagine. Brains aplenty are not a better survival kit than a good set of claws and fleet feet. Primate and corvid level brainpower seems to evolve (when it does at all) as a second-best compensation in creatures lacking those more desirable attributes. The weight/power/wingspan mechanics of flight are a restraining influence on the size of brains in flighted birds, so our avian friends might have peaked with crows and parrots. However, once upon a time there existed close relatives of birds without wings; they had dexterous claws instead.
A bipedal dinosaur called Troodon formosus was about two meters from nose to tail and weighed some 50kg (110 lbs). The troodon is closely related to known feathered dinosaurs, though we don’t know if it sported feathers of its own. The size of the brain case indicates it was pretty bright by dino standards. It might have been able to outwit an opossum (had there been any opossums). Maybe. This is impressive enough to have set paleontologists Dale Russell and R. Seguin back in 1982 thinking about how evolution might have proceeded had that asteroid not killed the troodons and other dinosaurs 65 million years ago. In full expectation, I’m sure, that the popular press would pick up on the story (scientists love the spotlight as much as anybody), in 1982 they published an article in which they described a hypothetical dinosaur with human-level intelligence. Troodon sapiens (pictured below with its ancestor) bears a striking resemblance to ET, but its body type is very human-like. Arguing from the principle of convergence, which is what makes dolphins look like fish even though they aren’t, they concluded there are predictable developments over time in body shapes. A humanoid form, they suggested, has many advantages for an intelligent species and nature therefore would tend to select for it.
Paleontologist and science writer Stephen Jay Gould reacted at once with annoyance. He said that convergence is the exception, not the rule, in evolution. The rule is divergence. Convergence happens only in response to very specific environmental pressures (e.g. a streamlined shape for swimming). No such pressures tie intelligence specifically to a humanoid shape. Humans owe their body form to their peculiar primate ancestry. Accident and chance dominate the evolution of life; if the K-T (Cretaceous-Tertiary) boundary asteroid never had struck, he argued, subsequent lifeforms and the shape of any intelligent ones would be impossible to predict. He added that human-level intelligence arose only once on earth, which suggests it is a low probability event anyway.
Paleontologists on both sides of the issue talked at each other, but as is usual in such debates, no one did much convincing of the other. The debate hasn't ended yet.
I side with Gould on this one, but I do enjoy conjuring the image of a troodon-like dinosauroid on some parallel earth sitting in his study and writing a poem with the refrain, “Quoth the monkey, Nevermore.”