Joshua Lederberg discovered that, in a large population of Escherichia coli (E. coli) about 1 in 10 million of the offspring was naturally resistant to the antibiotic streptomycin. When these naturally resistant bacteria were isolated and grown separately, they soon formed a larger population. The entire population so formed was also naturally resistant to streptomycin.
The formation of the large streptomycinresistant population is based on
(1) variations and survival of the fittest
(2) mutations and asexual reproduction
(3) sexual reproduction and no mutations
(4) survival of the fittest and cloning