Sentience and sensation.

When animals are used in a biomedical research activity that may result in more than mild or momentary pain or distress, humanity, federal regulations and common sense direct us to use the least sentient species that can fulfill the aims of the research. The use of a less-sentient species is in line with the concept of Replacement, one of the well-known 3Rs of laboratory animal use. But what is a less-sentient species? Is a chimpanzee less sentient than a human; is a dog less sentient than a chimpanzee; and is a mouse less sentient than a dog? Does 'less sentient' imply that a species is less able to experience pain, is less intelligent or has less self-awareness? This essay will explore some of the relationships between sentience, pain and vertebrate phylogeny.