Technical Abstract: Trappins are a family of small secretary host-defense peptides that have many functions. Most members exhibit antiprotease and antimicrobial activities, while others influence inflammation, immunity and the promotion of tissue repair. Considered to be important guardians of mucosal surfaces, trappins possess an N-terminal transglutaminase substrate (TGS) domain and a C-terminal whey acidic protein (WAP) four-disulphide core (WFDC) domain. The numbers and compositions of trappin genes vary among eutherian mammalian species. While there is a single trappin-2 gene in human and sheep, no trappin gene was found in mouse and rat. By contrast, multiple duplicated trappin paralogs were found in pig, cattle, guinea pig, armadillo and Afrotherian species (elephant, tenrec, and hyrax). Trappin duplication events appear to have occurred independently in these mammalian lineages over a long time period, suggesting their potential roles in species formation and animal domestication. Recent duplication and accelerated evolution of trappin genes in pig, cattle and armadillo demonstrate that mammalian genomes have the capability to form trappin multigenes to acquire antimicrobial activities for niche-specific pathogens.