Apparently the native people of St Kilda had developed a genetically inherited elongated big toe that let the men cling more easily to the cracks in the rocks. On one side of the island is the Mistress Stone where marriageable men had to balance on one leg – on the edge of a 300 ft drop – to prove their agility on the rocks and their ability to support a family.
Source: “West Coast” by Kate Muir