Rudolph Virchow, the 19th-century German neuroscientist, physician and political activist, came of age with two dramatic events--a typhoid outbreak in 1847 and the failed revolutions of 1848. Out of those experiences came two insights for him: first, that the spread of disease has much to do with appalling living conditions, and second, that those in power have enormous means to subjugate the powerless. As Virchow summarized in his famous epigram, "Physicians are the natural attorneys of the poor."

Physicians (and biomedical scientists) are advocates of the underprivileged because poverty and poor health tend to go hand in hand. Poverty means bad or insufficient food, unhealthy living conditions and endless other factors that lead to illness. Yet it is not merely that poor people tend to be unhealthy while everyone else is well. When you examine socioeconomic status (SES), a composite measure that includes income, occupation, education and housing conditions, it becomes clear that, starting with the wealthiest stratum of society, every step downward in SES correlates with poorer health.