Functionally important traits in animals tend to vary little
from one individual to the next within populations, possibly
because individuals who deviate too much from the mean have lower
fitness. If this is the case, does variance in a trait rise after
it becomes less functionally important? Billet et al. (2012)
investigated this question with the semicircular canals (SC) of the
three-toed sloth (Bradypus variegatus). The authors
proposed that since sloths don't move their heads much, the
functional importance of...