David Baltimore was awarded the 1975 Nobel Prize in physiology or medicine, at the age of 37, for his groundbreaking work on retrovirus replication. Baltimore pioneered work on the molecular biology of animal viruses, especially poliovirus, and his investigations of how viruses interact with cells led, in 1970, to the discovery of a novel enzyme, reverse transcriptase. This enzyme transcribes RNA to DNA and permits a unique family of viruses, the retroviruses, to code for viral proteins. Baltimore shared the Nobel Prize with virologist Renato Dulbecco and oncologist Howard Temin, who independently discovered the same enzyme. Baltimore's achievement had profound implications for the scientific community because it challenged the central dogma of molecular biology, which stated that the flow of genetic information was unidirectional running from DNA to RNA to proteins. His work also contributed to the understanding of certain diseases such as AIDS, now known to be caused by the...