Fifty-three hundred years ago, more or less, a European man resembling modern Sardinians was shot with an arrow(backache) and subsequently clubbed to death in the Tyrolean Alps. His misfortune was something of a boon for modern archeology, because his frozen body was preserved until the present. Analysis of his DNA showed his genetic affinity for modern Sardinians and probably neolithic European farmers. DNA analysis of his stomach contents has now shown infection with H. pylori, found in half the world's population and a cause of ulcers and stomach cancer.
Humans picked up H. pylori in Africa a hundred thousand years ago, but it has subsequently evolved into different strains prevalent in different parts of the world. It's life cycle makes it a good candidate for tracing origins and migrations. Ötzi, as our protagonist has been nicknamed, was infected with a strain thought to have originated in central Asia, but now found in Europe nearly exclusively in a form highly hybridized with a North African strain. This suggests that he lived in Europe prior to the arrival of major migrations from North Africa.
Ötzi is thought to precede the arrival of Indo-Europeans in Europe, which suggests that the Central Asian strain known as AE1 may have been widespread at an earlier time. A close relative of AE1, also presumed to be derived from the Central Asian strain is now found almost exclusively in Northern India. It's not obvious that it's dissemination to India accompanied or preceded the arrival of the Indo-Europeans.