Final answer:
Studies of proteins at the evolutionary scale focus on the 3D folding patterns and genomic sequences, with protein folding providing robust insights into their evolutionary relationships.
Step-by-step explanation:
The two principal evolutionary scales investigated in studies of proteins are structural evolution, particularly the three-dimensional (3D) folding patterns, and genetic evolution, which looks at the genomic sequences. The study of protein structure has revealed that the folding of proteins provides a more thorough understanding of evolutionary relationships than DNA sequences alone. This is because proteins can maintain similar 3D structures despite having divergent amino acid sequences, as seen with rabbit skeletal muscle actin and bovine ATPase. The fold of a protein is an evolutionarily conserved element that plays a significant role in its functionality, and analyzing protein structures has been crucial for understanding the mechanisms behind disease and for pharmaceutical drug development.