Biased Choice of Criteria

In response to Brian Fitzpatrick's post "Response to 'Initial Thoughts'" (2/2/2013):

In reply to one of my posts, Brian brought up the concept that value exists on a sliding scale.  He suggested that the ability to remember one's past gave one value in addition to the preexisting value generated by one's ability to value oneself.  This made me wonder which other qualities can grant value in addition to that basic value shared by all sentient beings (or subjects-of-a-life, to use the lingo).

My initial thoughts included such qualities as the ability to record history (as with written language), a social structure, the ability to create lasting monuments or other physical mementos, and the capacity for rational thought.  However, on second glance I wondered if I might be biased.  The aforementioned qualities are certainly valuable by a human standard, but since this whole argument began with one's ability to value oneself, is it fair to judge the value of other animals by a human standard?  Dolphins, as examples of members of an extremely intelligent nonhuman species, do not typically create lasting structures and do not record their history, yet they are undoubtedly very high on the sliding scale of sentience - irrefutably higher than either beavers or termites, both of which produce rather formidable structures.

I am not sure how to determine, then, which qualities we should give consideration to when deciding how much value to place on any given type of animal.  Some, like Brian's suggestion of memory, seem obvious, but others are not so.  When there is only a slight difference in attributes between one animal and another, what can allow one to differentiate between the values of the two?