The term "pain" needs to be defined more precisely -- everyone is either using different definitions or definitions so vague as to be useless. On one hand, you have autonomous biological responses to trauma, which could be construed as "pain" but which have no requirement for intelligence, consciousness, or awareness in the definition. On the other hand, you have the definitions of "pain" that depend on some level of high functioning consciousness, therefore requiring a significant amount of higher brain function. All animals fall somewhere in the spectrum between the two, largely as a function of central nervous system development.
Any medical expert will tell you that a fetus exhibits the former type of "pain" response very early on. At the same time, anyone that knows anything about human CNS development can also tell you that the latter type of "pain" does not fully develop in humans until one or two years *after* birth. A human is born with negligible higher brain function, so it would be hard ascribe much in the way of high-level perception of pain unless one grants that level of perception to most living critters.
It will be hard to have a meaningful conversation with the medical community until everyone agrees on a more rigorous definition of "pain" for the sake of discussion. Technically, all the doctors you disagree with may be absolutely correct if one accepts their definition of pain, generating all heat and no light until these differences are resolved.
Thanks for the clarification. However, I remain confused. The definition of higher level functioning version of pain seems tautological and at odds with commonsense observations. The definition of higher functioning definition of pain suggests that one and two year olds do not feel pain. This on the face of it is absurd as any parent with a teething baby well knows. Also what does "fully developed" mean? A baby's hand is a hand, but it obviously is less developed than an adult's. Does this mean that it is not a hand?
Moreover, if there are two definitions and one is more objectively measurable than the other, shouldn't we go with the more measurable, at least until we can arrive at a less arbitrary definition?
Clearly there are some tricky definitional issues here - but IMHO Dr. Derbyshire's review article remains highly problematic and his policy conclusions clearly questionable and necessarily dictated by his very definition of pain.