Relaxin family peptide hormones in humans are represented by 7 members: three relaxin-like (RLN) and four insulin-like (INSL) peptides. This subdivision into 2 classes (RLN and INSL) is based primarily on early findings and does not reflect the evolutionary origins or physiological differences between peptides. For example it is known that the genes coding for RLN3 and INSL5 arose from one ancestral gene and INSL3 shares origin with RLN2 and its multiple duplicates (e.g. RLN1 INSL4 INSL6).
