Most of our conceptions of religious expression are fundamentally based on practices that are biologically human. For instance, religious books or texts require literacy, which in turn requires the development of abstraction coupled with a language–all of which resulted from increased brain size. Congregational worship is reasonable for our species since we are biologically social creatures, and our primate hierarchies form a convenient basis for the worship of a personal God.

What about other creatures, though? If squirrels, dolphins, and owls are spiritually active, how could we tell? Since most outward expressions of human religiosity are based on biologically human traits, it seems that we are largely unqualified to identify non-human spirituality by simple comparative means.

Given that we do not see these obvious parallels between human and non-human spirituality, we are led to one of three conclusions:

1) Spirituality is a result of intelligence (or some other uniquely human biological trait)

2) Non-human spirituality exists with qualities unique to each species/sub-community

3) Humans alone possess a divine spiritual gift (e.g., an immortal soul)

#1 suggests spirituality is a biological peculiarity and likely absent in non-human communities. #3 is a popular religious assumption, implying the dominion of humanity over the biosphere. Given our inability to find non-human spirituality with the comparative method, #1 and #3 are the most commonly believed conclusions; yet the absence of evidence is almost never a strong argument. Perhaps spirituality is uniquely human, but then again perhaps our religious experiences are so narrow that we constantly overlook the signs of spirituality outside of our realm.