Do scientists consider elementary evolutionary material?

According to the synthetic theory of evolution (neo-Darwinism), any transformation always affects the genotype. Selection works with phenotypes, selecting those that are best suited to the environment. The phenotype is based on the genotype (DNA). But selection must, in fact, be given the opportunity to select. In other words, the variability of those genes is necessary, on the basis of which different variants of the phenotype are obtained. Mutations are responsible for gene variability or variability. Mutations should not be understood as DNA damage. In essence, they are neutral (occasionally only harmful or only useful ones appear) and acquire their color of “harmful” or “useful” in different living conditions of the organism.
For example, a mutation in the Agouti gene in hamsters results in a version of the gene that makes the animal’s color lighter. In wooded areas, this is clearly a deleterious mutation that reduces fitness. Due to their light color, hamsters are easier to spot in the forest. But this mutation will be useful for those who live in desert areas. Because of this mutation, the original population of brown hamsters was once divided into sandy and forest hamsters. Since there were several variants of the gene and, as a result, different phenotypic effects, the selection had material with which to work and select those individuals that turned out to be the most successful in terms of reproduction in specific conditions.
Answer: mutational variability.