Rats on 22.5-hr light:dark cycles have vaginal opening earlier than rats on 26-hr light:dark cycles.

Rats on 22.5-hr light:dark cycles had vaginal opening significantly earlier than rats on 26-hr light:dark cycles. This finding might explain the early menarche in blind girls: Their circadian rhythms, like those of rats on 22.5-hr cycles, might be more rapid than normal. Thus a set number of cycles can occur in a shorter time than usual, allowing puberty to take place early.