The SMAD proteins are homologs of both the drosophila protein, mothers against decapentaplegic (MAD) and the C. elegans protein SMA. The name is a combination of the two. During Drosophila research, it was found that a mutation in the gene, MAD, in the mother, repressed the gene, decapentaplegic, in the embryo. The phrase "Mothers against" was added since mothers often form organizations opposing various issues e.g. Mothers Against Drunk Driving or (MADD).
^Watanabe TK, Suzuki M, Omori Y, Hishigaki H, Horie M, Kanemoto N, Fujiwara T, Nakamura Y, Takahashi E (June 1997). "Cloning and characterization of a novel member of the human Mad gene family (MADH6)". Genomics42 (3): 446–51. doi:10.1006/geno.1997.4753. PMID9205116.