I received a very interesting question via email from Patrick Chan:
According to the theory of evolution, why couldn't future man be materially different from present day or modern man, such that he is no longer distinguishable from modern man (by "materially," I include genetic and biochemical differences which may or may not manifest themselves physically)? As far as I can tell, it's possible according to evolution.
And perhaps as a result of such differences, why couldn't future man differ markedly from modern man in other ways? Maybe future man will have a different psychological makeup and emotional life, for instance, and thus be subject to and experience different temptations, sufferings, etc. than what modern man experiences.
What I'm getting at is that it's possible Christ himself might not share with future man what he shares with modern man. It's possible Christ would no longer be "one of us" in the sense that he would no longer be able to share in future man's "humanity," assuming future man can at least still be considered part of the mammalian species homo sapien. (Of course, if future man is so different that he can no longer be classified as a homo sapien, then that raises other questions.) This would undercut Scripture (e.g. Heb. 2:14-18; 4:15-16).
In other words, if it's possible for man to evolve into something different than he is today -- whether it's only a slight difference or whether it's as jarringly dissimilar as depicted in a movie like 2001: A Space Odyssey (in which man is a different species) -- then what would that make Christ in his incarnation as a man? On the evolutionary tree of life, modern man, and therefore Christ himself since he came as a modern man, could very well be to future man what an ape-man might be to us. Evolutionarily speaking, Christ in his incarnation would be a different being than future man. I'll not mince words: as far as I can tell, it's possible that the evolutionary equivalent of an ape-man might have died for your sins.
My response (addressed to him, since I first wrote it in an email response to him):