It seems like most people don't know that DDT was developed during World War 2 to protect soldiers from lice and fleas. After the war it was used to kill other insects that caused people to die. So, many lives were saved and the African population increased greatly. But there was an unknown price at the time. It took some years before Carson's book came out. It was discovered that many birds were laying thin shelled eggs which got broken in the nest and bird populations were decreasing. DDT residues were found in the food chain as well and nobody knew what the results might be, so. limitations were put on how much could be in the food we ate.