Is it an 'essential?'

Our small group is going through the book "The Reason for God: Belief in an Age of Skepticism" by Timothy Keller. The chapter we discussed last night was on the topic of Science vs Religion, and the idea that 'Science has disproved Christianity.' The two main topics in this chapter were on the Origins of Life and Miracles. Keller proposes that whatever one believes in the Origins of Life isn't one of the 'core essentials' of Christian belief. Therefore, if someone is considering Christianity, they shouldn't get hung up on the differences of opinion on this topic. On the surface, this makes a whole lot of sense, and I initially agreed with it. But after giving it more thought, I'm not so sure. I woke up this morning with the question,  "If we Evolved, why did Jesus have to come and die?" and it has been bothering me all day.

Here's the disconnect I see:

The reason that Jesus had to come and die was because humanity is Fallen. The common understanding/belief about this is that humanity at one point experienced perfection, and chose to disobey God, thus ending that perfect life. Christ came to pay the penalty for that disobedience and restore humanity to that perfection.

If we Evolved from some primordial lifeform, at what point did we attain a soul, and at which point did we become Fallen, thus requiring Christ's sacrifice? Also, who was Adam? If he was the first 'homo sapien,' what differentiated him from his predecessor, and why has humanity suffered because of him? And if, hypothetically speaking, he had a brother, were his children free from that Fallen condition? Romans chapter 5 talks about Death/Sin entering the world through Adam and makes a comparison to the Salvation that entered the world through Jesus, "For if, because of one man's trespass, death reigned through that one man, much more will those who receive the abundance of grace and the free gift of righteousness reign in life through the one man Jesus Christ."

I am trying to rectify the Evolutionary process with verses like this which refer back to a single point of failure. If 'Adam' was just another step in the Evolutionary process, what made him so special that the rest of Humanity would suffer because of his action?

Maybe belief in our Origins is one of the 'core essentials' of Christianity....I'm still not entirely sure, but it is definitely something that is giving me much thought. I would appreciate any input you might have.

(For the record, I have spent a LOT of time over the years studying the topic of Creationism/Evolution, and I have concluded that the literal interpretation of the Bible (aka God spoke everything into existence in just six 24-hr periods) makes the most sense.)