Ten of amino acid sequences of ras p21 which come from human, fruit fly, yeast, Dictyostelium and virus were collected and analyzed. Data analysis indicates that: 1. the mean duplicate rate of ras p21 is approximately 2.78 x 10(-9) per gene per year for concerted evolution; 2. the mean amino acid replacement of p21 is about 2.23 x 10(-10) per year. It also shows that v-Has and v-Kis were derived from c-H-ras1 and c-K-ras2, respectively, and that c-H-ras1, c-K-ras2 and c-N-ras come from the same ancestor. These result are in accordance with the experimental results reported by other authors. According to the view of Fitch et al., we present here a speculative view for carcinogenesis mechanism the hypothesis for covarions and invarions, by which, the codon 12 or 61 mutated in p21 may be responsible for last one or more steps in carcinogenesis.