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It was long thought that bacteria multiply by dividing, so that all bacteria have the same genetic make-up. Joshua Lederberg and Edward Tatum demonstrated in 1946 that bacteria's genes can also change in a way similar to that of sexual reproduction seen in more complex organisms. Bacteria can go through a phase in which two bacteria exchange genetic material with one another by passing pieces of DNA across a bridge-like connection. Joshua Lederberg also proved the phenomenon known as transduction, in which DNA is transferred between bacteria via bacteriophages.