Doom sells.  Always has, always will.  One of the greatest purveyors of doom was Dr. Paul Ehrlich, who died last week at age 93.  In 1968, Ehrlich wrote his famous screed ‘The Population Bomb,’ which became one of the most influential books of the 20th century.Doom sells.  Always has, always will.  One of the greatest purveyors of doom was Dr. Paul Ehrlich, who died last week at age 93.  In 1968, Ehrlich wrote his famous screed ‘The Population Bomb,’ which became one of the most influential books of the 20th century.