I came across a very interesting series of articles at macroevolution.net by a Dr. Eugene McCarthy with a PhD in genetics. He specializes in cross-species hybridization (he has a book on avian examples), and he makes a thought-provoking argument that because humans share so many traits uncharacteristic of the great apes and that many of these traits are similar to those of a particular non-primate mammal that the traits are best explained by an extremely unlikely hybridization event. It sounds more than a little “monkey-fish-frog” (or man-bear-pig, if you get that reference), but even if the conclusion seems absurd, the evidence he brings up is compelling, the unlikelihood of a successful hybrid stabilization event notwithstanding.
There are many things about this theory (along with the reactions to it) that are engaging. One is the following angle: How well does Dr. McCarthy’s evidence support considering the human genome as a intentional incorporation of specific pieces of non-primate DNA into the basic ape architecture in a way that required specific knowledge of the architecture? That is, how much does it resemble a deliberate engineering effort? (Aside: Some groups might be more supportive of pig-chimp theory if it declared that "all men are pigs" at the exclusion of the female gender.)
With all the evidence that McCarthy trots out, it seems like a wonder that humans are considered so closely related to apes. Think of the paleontological primacy of bone structure and how it is undermined by marsupial phylogeny. Based on bone structure alone, it would be impossible to realize how different many marsupials are from their convergently evolved placental counterparts. Dr. McCarthy has begun to question the assumptions of paleontology (if it's really old it must be something like a lizard) and whether some dinosaurs should be considered to be much more like mammals than reptiles. (And how long did it take for paleontology to accept the idea that some dinosaur creatures could be more avian than reptilian?)