With respect to medicine, the 19th century was about developing a basic understanding of hygiene. The 20th century was about understanding major diseases and the development of medicines, surgical procedures and analytical technologies to treat them.
Advances in medicine will continue, of course, but the priority for the 21st century, in the developed world at least, is behavior.
If people in developed societies would eat less, consume less alcohol, stop smoking, exercise more and put down their cell phones while driving, it is estimated that health care costs would decline by at least a third. This is not a fool's errand. The decline in smoking over the last 20 years is proof that behavioral patterns, even deeply ingrained ones, can be positively altered. It is not written in stone that people must just keep getting heavier or that texting while driving is so addictive that people are somehow incapable of resisting the urge to drive 70 miles an hour while googling directions to a pizza parlor. Self destructive behaviors can change if the government, corporations and the public are aligned.
Recently Mayor Bloomberg attracted considerable attention with his proposal that New York City ban the sale of super sized drinks. Opinion is divided on this initiative and it may or may not be enacted by the City Council. On the other hand, regardless of the outcome of this particular proposal, the debate about the role of government in encouraging or dictating healthier habits is only getting started.
By the way, for those who think New York City is a less healthy environment in which to live, Mayor Bloomberg points out that city residents enjoy a lifespan that is 2 1/2 years greater than the national average.