* Proteins were known to be diverse and complex: Proteins were understood to be the building blocks of cells, with a wide variety of functions, including structural support, enzymatic activity, and signaling. This complexity suggested they were the logical carriers of genetic information.
* Nucleic acids were thought to be too simple: DNA and RNA were known to be relatively simple molecules compared to proteins, with only four different nucleotide building blocks. This led many scientists to believe they couldn't possibly hold the vast amount of information needed to code for all the diversity of life.
* Proteins were the "workhorses" of the cell: Proteins were observed to be directly involved in virtually all cellular processes. It seemed logical that they would also be the key to inheriting and transmitting those processes.
* Early experiments supported this view: Some early experiments, such as those by Frederick Griffith in 1928, suggested that a "transforming principle" could be transferred between bacteria. This principle was later discovered to be DNA, but at the time, the focus was on proteins as the likely candidate.
However, this belief was later overturned by groundbreaking experiments by Avery, MacLeod, and McCarty in 1944. They demonstrated that DNA, not protein, was the transforming principle in Griffith's experiment. This finding, coupled with other evidence, eventually led to the understanding that DNA is the carrier of genetic information.
The initial focus on proteins was understandable given the knowledge of the time, but the discovery of DNA's role in genetics revolutionized our understanding of heredity.
