(please excuse the English)

Reducing and confining “life” to a psychophysical phenomenon, whence including only high-cognitive abilities, is a major flaw in common discourse. Human are first and foremost _sentient_ being, much the same as other “inferior” creature, all the way “down” to worms comprising less than 1000 cells, that react spasmodically to light or touch. Ignoring the very basic nature of emotions or feelings can lead to a myopic understanding of other creature’s nature, and ours. As such, it was strongly suggested that our morality is based on the emotional capacity, and the recognition of such innate functions in other creatures might be enough to include them within he realm of our moral and ethical code of conduct. Hence, there are no ”pure” or “externally mandated” criteria where the line should be drawn, since we operate in an ever-shifting sand dune. Our stance keeps changing with culture, with what we, as individuals and as member of a certain group, feel “positively” about.

"The problem may be expressed in the form of a dilemma that can arise for any psychological research that uses animals for the human case. If the animal subjects are not sufficiently like us to produce a model, then the experiments may be pointless [...]. But if the animals are enough like us to provide a model, it may be impossible to justify treating them in ways we would not treat humans. The researchers are caught in a logical trap: in order to defend the usefulness of research the must emphasize the similarities between the animals and the humans, but in order to defend it ethically, they must emphasize the differences. The problem is that one cannot have it both ways."
(James Rachels, "Created from Animals", p.220)