Dr Boyd showed that when punishers were introduced to the mix, even if they started in only one group, their strategyspread rapidly through the population.
While hand washing and covering sneezes are parts of a larger strategy to prevent the spread of influenza, influenza vaccine continues to be the best way to protect against the disease.
President Bush's Proliferation Security Initiative is an example of a global strategy for dealing with the spread of chemical, biological and nuclear weapons and missile-related materiel and technology.
About a year ago, economic forecasters claiming insight into Fed deliberations spread the word that the central bank had devised a methodical exit strategy to unwind its balance sheet.