The Brain Transplant Argument

[Philo]

Animalism is the thesis that each of us is numerically identical to a human animal (e.g., you are identical to the human animal reading this post right now), and that each of us persists just in case the biological functions that sustain the life of the human animal we are identical to continue. Since the persistence conditions for animals in general are biological and not psychological, according to animalism the continuation of our mental lives is irrelevant to our persistence. This is a minority view among philosophers writing about personal identity.

The following argument, called the Brain Transplant Argument (BTA), has been advanced against animalism (its reconstruction here is taken from Paul Snowdon, "Personal Identity and Brain Transplants"):

(1) It is not absolutely impossible that our brains should be transplanted into new receptacles while retaining their intrinsic functions. (The intrinsic functions are the processes that characteristically occur in the brain, and which are assumed to sustain a mentally endowed subject.)

(2) Amongst the brain’s intrinsic functions is that of sustaining a subject with thoughts, apparent memories, beliefs, (etc.), and so such a rehoused and functioning brain will sustain a subject of experience who has psychological links to the donor subject.

(3) The total system, of which the rehoused brain is a functioning part, is not the self-same animal which donated it.

(4) The resulting subject sustained by (or realized by) this system would be the same subject (or person) which that brain previously sustained.

Do you think that BTA shows that animalism is false?