If evolution has produced the human being as we know it today, doesn’t that mean Jesus cannot be the perfect sacrifice because He was less evolved (primarily in mental capacity) than the versions of humans that came after Him?
This is an extremely difficult question and truly deserves a much deeper and more thorough answer than I am capable of supplying. While the question seems straightforward, there are basic assumptions buried in it which need to be addressed. The first is that evolution is (as the name implies) a static upward process; that is species are always developing for the better. The only way this can be remotely true is if God is directing the process which would then undermine part of the logic of the question since Christ’s redemptive work is part of the same system. While reading Homer or the Psalms should satisfy anyone that humanity has no greater mental capacity today than it did in Jesus’ time or before, the argument can be made that eventually humanity will be substantially different or a new species might attain rationality and so we should deal with the theological aspects of the question. Such a question also limits the definition of human to one physical characteristic. If we take Genesis 1 & 2 seriously then physical characteristics are not essentially what define a human; rather, humanity is defined by possession of God’s image, and as Jesus possessed this attribute that made him fully human. This means that being human is about being God’s image bearer not about certain mental capacity or certain appearance, humanity might change slightly, but, not at its core because its core transcends a physical dimension. (On a side note it was similar thinking that led some to espouse the theory that Africans were subhuman because they possessed “less evolved characteristics”).
The real problem with this question is that it defines Christ’s work far too narrowly, highlighting one element or metaphor (Christ’s substitution for humanity as found in Hebrews) without considering the rest of Christ’s work. If the only concept of Jesus’ work were a sacrificial death as the perfect human then we might be boxed in slightly and we might have some serious questions about the relationship between Christianity and science. But the New Testament uses several concepts to attempt to describe the work of Jesus on the tree. Among these is the concept of conquering king (John 16:33) and the one who created (Colossians 1:16) and thus restores all things (Romans 8:19-23). God’s ultimate plan goes far beyond merely the salvation of humanity by paying a ransom for sin (though that is certainly part of the plan). God’s plan is to restore creation to the sinless state, and to do so the sinless creator entered the world to begin the transformation. If we understand this, then all of creation, including humanity and whatever might possibly evolve, is saved and restored. (For more on the work of Jesus see N.T. Wright Simply Jesus and Surprised by Hope).
We see this wonderfully illustrated in C.S. Lewis’ Space Trilogy, all of creation (even beyond the bounds of earth) is well aware of what Christ accomplished and how it changed everything. Even the creatures who do not look anything like humans celebrate Christ’s work. The story shows that creation turned a corner in the Incarnation; and that Christ’s redeeming work is truly for all creation including all creatures who bear the image of God, no matter what they look like.
This response is little more than a basic outline, further details can be found in the resources mentioned as well as these:
John Polkinghorn and Nicholas Beale, Questions of Truth which has an excellent bibliography
Denis Alexander, Creation or Evolution: Do We Have to Choose?
Scot McKnight, Adam and the Genome