And why not? It's an area where it may be possible to tie a can to the tail of an examiner who has not carefully thought out responses. (Yeah. I know sophisticated defense attacks are uncommon, but we prepare by anticipating the worst.) Of the two issues, uniqueness and permanence, uniqueness is the most vulnerable. Permanence, barring trauma, is implied by what's known of skin development. It's not a total scientific lock, but an attack on permanence sounds desperate. And, of course, uniqueness is the "core value" of latent print comparison.L.J.Steele wrote:Are you still getting legal challenges to uniqueness and permanence?
I think that, no matter which answer might be given to this question, aside from seeing that it is something the jury can handle (not c.), the answer has to be consistent with the other testimony about the conclusion. There is no true answer that can demonstrate proof that for some arbitrarily sized area of skin, there is no other area of skin that can make a usable impression that cannot be differentiated. Even the "good" answer, d), makes use of an unprovable statement of impossibility.
The point is not so much about absolute uniqueness but about how all that is known and has been observed about friction ridge skin makes very strong conclusions possible. When you get into this sort of questioning, I think it's important to avoid leading to an admission that uniqueness is presumed, rather than proven, and having that used in a chain of argument designed to poison the conclusion in the minds of the jurors.
My answer, which presumes I might not get to talk about the details of ridge formation in other answers:
e) From medical research, we know the ridges form while an embryo is in the womb and that they form as emerging pores line up in particular ways in response to changing pressures in the tissues. These studies suggest that there are so many variations in how this may happen in an individual that identifiable differences will always be present. This is supported by an enormous number of observations over many, many years. And because the formation of friction ridges is complete before birth, there is no known way for these formations to reform over time. This is also supported by both incidental observations and specific studies.
I stay well within what is known and make no unprovable absolute claims, and I set up the basis for a high level of confidence in my conclusion.