The hybrids were bred again with deer mice, and the type of burrows those "backcross" offspring made show the inheritance patterns of the behaviours - and strong hints of how many genetic changes are required to modify it.

BBC: Mouse burrowing 'in their genes'

The team carried out a preliminary genetic analysis of the backcross mice, and showed that the propensity to dig long burrows is actually due to changes in three genetic regions, with a fourth region controlling the escape route behaviour.

BBC: Mouse burrowing 'in their genes'