Abstract: In terms of the theme of synthetic theory of evolution, biologists are divided into two schools, the defenders and the challengers. The defenders aim to solve abnormal problems by amending and protecting, so as to defend the legitimacy of the synthetic theory of evolution. However, the challengers hope to construct extended evolution theory to replace the synthetic theory of evolution. Therefore, defense and challenge constitute two different evolutionary paths of the synthetic theory of evolution, showing a trend of dual evolution.