The author also asks what would have been in the minds of those who saw these hairy girls. Europeans of the 16th century still inhabited a pre-scientific world, where natural events were pregnant with meaning and open to all kinds of interpretation. Every individual was significant as part of a planned, coherent universe. As a result, there was intense interest in freaks and monsters - what did they mean? Were the hairy girls a warning of divine displeasure with a sinful age, a sign of impending apocalypse? Or perhaps they had been conceived while their mother was lying on a bearskin rug?

What emerges most clearly from this book is the 16th century's capacity for wonder - suspended between the pre-modern and modern worlds, they were surrounded by the unknown, in the as yet uncharted areas of the world beyond Europe and the workings of their own bodies. In such a world of unknowns, hybridity was dangerous as well as fascinating. The Gonzales sisters blurred the accepted boundaries between one thing and another. Were they civilised people or wild savages, courtiers or domestic pets?

Wiesner-Hanks follows the sisters' story wherever it leads: to the writings of Martin Luther, the prophecies of Nostradamus and the fashion for the monarch to be followed by a retinue of dwarves. These digressions, paired with speculations about the girls' thoughts and actions, could easily seem tenuous or contrived, but an eye for gripping details and a formidable grasp of the material make it work. She highlights the unknowns in the story: women disappear from the records after marriage, a medical student leaves out the most gruesome details of an autopsy and a non-hairy Gonzales brother is mentioned at his birth, then never again. The fact that these details are lost to us is itself evidence, which she uses to speak for the voiceless as well as for history's great men.