Things I don't understand episode 2000: Why in comparing humans & other animals the null hypothesis people always use (and thus try to disprove) is that humans ≠ animals

Well, this is something I just do not understand.  I am sure others out there have thought about this more than I have.  Just read this article: Considering the Humanity of Nonhumans - NYTimes.com discussing humans vs. non human animals.  And there is this extensive discussion in there about whether animals have self awareness, and whether they deserve legal rights, and such.  All very interesting I think.

But one part I do not understand.  It is very clear that humans and other animals have many homologous features.  It is very clear that humans are more closely related to some animals (e.g., primates) than to others.  For many comparative studies of animals, if one wants to claim that some animal has a feature that is different from it's close relatives, it is frequently up to the person proposing such a difference to disprove the null hypothesis that the close relatives are the same.  This is the case when studying molecular processes, cell structures, physiology, genome structure, and so on.

Yet, there are a few biological features regarding humans for which it seems the null hypothesis everyone is forced to work with is the reverse.  In these cases the null hypothesis is that we (i.e., humans) are unique and those who wish to claim that humans and other animals are similar / the same have to disprove the null hypothesis.  This seems, well, awkward, at best.  Basically, for some features - especially those that relate to intelligence and behavior  -  if one wants to claim that they are not unique one has to disprove the null.  And yet, for all other features, the null hypothesis is that humans are not unique and those wanting to show uniqueness are forced to disprove this.  On the one hand, I get this.  There are many reasons why one might want to treat "humans are unique" in regards to intelligence and behavior - as the null hypothesis.  But on the other hand - this seems exceptionally anthropocentric and has almost certainly prevented us from discovering and understanding certain behaviors and intelligence-related issues in non human animals.  How do we as a community decided which null hypothesis to use for each phenotype?

Anyway - there it is.  Something I do not understand.