For bacteria to evolve by beneficial mutations one at a time would take much, much longer than three or four billion years, the time that many scientists believe life has existed on earth. ”
कई वैज्ञानिक मानते हैं कि धरती पर जीवन की शुरूआत आज से करीब तीन या चार अरब साल पहले हुई ।