Fruit flies have a pigment in their tiny brains that allows them to tell the difference between night and day, according to new research. Scientists previously understood how six biological pigments called rhodopsins in the eyes of fruit flies allow them to filter light, discern objects and detect temperatures. But the study published in the journal Nature today described how a seventh rhodopsin expressed in the flies' central brains was important in discerning night from day.

Why you should care: The discovery could teach researchers how to deal with degenerative disorders that affect human vision.

Explain the science: Photopigment rhodopsin in human eyes intercept light as the first step in a biological process to actually perceive light. Now that scientists know fruit flies also have a seventh rhodopsin expressed in their brains that works in this light-filtering process, they hope to be able to better understand (and eventually treat) retinitis pigmentosa and other degenerative eye diseases in humans.

How they did it: Researchers disabled the seventh rhodopsin in some fruit flies and discovered that they couldn't adjust to circadian rhythms the way normal fruit flies could, confirming the pigment's role in adjusting to night and day cycles.