Baby Fae
Bailey's use of baboons was somewhat surprising, given their relatively distant evolutionary relationship to humans compared to other primates. The reason came to light when the Times of London published an interview between Bailey and an Australian radio crew. The reporters had been forbidden to ask direct questions about the operation, so they queried Bailey on the issue of why he had chosen a baboon in view of the baboon's evolutionary distance from humans. Bailey replied, "Er, I find that difficult to answer. You see, I don't believe in evolution."6
Ancestry did not cause the rejection. Present immunology and differences in genetics caused it.
UCD might prove useful in helping to familiarize a doctor with similarities and differences between diverse life forms, but this is not an indication that UCD caused these differences and similarities. I can organize words alphabetically, but that has no bearing on how the words actually originated.
Common ancestry does not necessarily make rejection less likely. Take blood transfusion. A close relative will not necessarily be a better donor candidate than an unrelated stranger. What matters here is the characteristics of what is donated, not how closely related the donor actually is to the recipient.
You might also point out the role of common descent in picking out suitable test subjects for certain medical or clinical experiments and trials.