The concept of protein family was conceived at a time when very few protein structures or sequences were known; at that time, primarily small, single-domain proteins such as myoglobin, hemoglobin, and cytochrome c were structurally understood.
O concepto de familia de proteínas concebiuse nun momento en que se coñecían poucas estruturas e secuencias de proteínas; daquela, as que se comprendían estruturalmente eran principalmente pequenas proteínas de dominio único como a mioglobina, hemoglobina, e o citocromo c.