Scientists have studied twins since the 1870s, when Francis Galton began using them to separate the effects of heredity from environment. Because identical twins share nearly all their genes, comparing them with fraternal twins and the wider population helps researchers judge how much a trait is shaped by genes and how much by upbringing. Galton, a eugenicist, promoted twins as natural experiments, and in the 1920s German researchers used the identical and fraternal distinction to classify traits for race science. Later, a Nazi-era twin researcher's student, Josef Mengele, carried out experiments on twins at Auschwitz. Modern twin registries and NASA's 2015 study of astronaut Scott Kelly, compared with his twin Mark on Earth, continue the approach, which now comes with strict ethical rules.

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.