Answer
Darwin used the phrase survival of the fittest to reference any species that is most adaptable to its ever-changing environment and therefore lives longer and reproduces. Adaptability and reproduction are the most successful traits that lead to lineage. To discuss whether or not the concept of “survival of the fittest” is compatible with the Bible, we must pick apart the aforementioned premise.
Foremost, evolution is a theory developed within the construct of the “natural sciences.” It is one thing to discuss any kind of survival on natural terms amongst natural things (i.e., trees, dirt, and anything dealing with landscape) and an entirely different matter to apply the same criteria to humans, whom the Bible describes particularly as far more than natural.
The Hebrew word nephesh is used predominantly of humanity (Genesis 2:7; 7:22; Ecclesiastes 3:19). The Bible makes a distinction between what is naturally living only and what is also spiritually living. If we were to apply the idea of “survival of the fittest” to a spiritual context, it would fall short at the very least because it’s a concept out of its element—it’s too small of an idea to swim in the deep waters of defining the full scope of human existence. Evolution dumbs down human capacity, along with undervaluing all of creation.
Second, the idea of “fittest” suggests “better than.” This concept is foreign to Scripture because God measures everyone and everything against the same measuring stick: perfection. His perfection. There is none “fit” except for Him. Anything short of perfect does not compute when compared to the holy nature of God. Missing the mark of perfection is what the Bible calls sin, and every human and every corner of creation is infected with it (Romans 3:23; 8:19–24; 1 John 3:4). Sin at its core has corrupted and continues to rot the natural and spiritual order of things. We are not evolving but devolving. We’re getting worse.
Third, left to our own, without the gloriously reproducing promise made to Abraham's offspring—that God would bring about a family and a righteous people through Christ (Genesis 12:1–3; Galatians 3:16), we reproduce only destruction unless something or someone intervenes. Only God can intervene and bless humanity as we multiply for His sake because, without the gospel, multiplication is not the ally of sinful humanity, but our enemy. The more that the sinful human population expands historically, and from a theological perspective, the more pervasive and destructive sin becomes because we do what is right for us, not what is loving (Judges 21:25). Therefore, we see, for instance, in Genesis 12 that God had to intervene and did so more than once. In this instance, He comes to Abraham and promises him a “seed” of reproduction that will be of a perfect genus. This seed will grow up and crush the enemy and introduce an altogether different reproductive DNA into creation (Genesis 3:15). A perfect one. A healing one. A saving one.
This “seed” promised to Adam and Abraham—and whispered about to many others throughout the Old Testament—became a shout in the person of Jesus (Galatians 3). He gave us a perfect source, and through His lineage and His blood, we enter His perfect family line (Ephesians 1:7–10). It’s a family that lasts forever and is not just natural, but eternal.
We guess we could say that, through the “fitness” of one seed, Jesus, we “survive.”
