At the turn of the twentieth century staying alive to your sixties was still a lottery. In Britain improvements in sanitation and housing conditions helped but endemic diseases like tuberculosis, cholera and typhoid still killed rich and poor alike. Childbirth was dangerous and often fatal. Polio crippled thousands of children, while more people died in the worldwide flu epidemic of 1919 than were killed in the Great War. The most important medical discovery of the century was Alexander Fleming's discovery of penicillin. Suddenly infections that had killed or debilitated could be cured with a course of pills. This enabled surgeons to pioneer and perfect increasingly complex operations, culminating in the first heart transplant in 1967. Previously while surgeons could perform operations using anaesthetics infections could kill the patient. Antibiotics made it possible for more and more complex operations and worldwide vaccination and immunisation programmes all but eradicated smallpox and polio. Medical research really exploded after the Second World War as scientists discovered more and more about the nature of life itself. The first test tube birth was a calf in 1944, yet within 40 years in vitro fertilisation was a common, if not always successful procedure. Scientists have now successfully cloned a sheep leading to the possibility that human beings may be able to grow duplicates of themselves. The discovery of the DNA helix has resulted in scientists being close to mapping every gene in the human body. Supporters of the Human Genome Project believe that doctors will be able to treat hereditary diseases and pre-dispositions at its very source. Such genetic and bio engineering poses new ethical and moral questions. The explosion in computer and microchip technologies has spurred the development of nanotechnology. In the future tiny microscopic machines may be injected into the bloodstream where they can seek out the source of infections, diseases or cancers and eradicate them. In the past 200 years the average life expectancy of Britons has doubled. In the next 50 it may double again.