Horizontal gene transfer
Horizontal gene transfer was first observed in 1928, in Frederick Griffith's experiment: showing that virulence was able to pass from virulent to non-virulent strains of "Streptococcus pneumoniae", Griffith demonstrated that genetic information can be horizontally transferred between bacteria via a mechanism known as transformation. Similar observations in the 1940s and 1950s showed evidence that conjugation and transduction are additional mechanisms of horizontal gene transfer.