If it is true that...

The organism runs according to a genetically determined "clock" located in certain cells in a specific area of the brain

Then it must be true that...

Nervous impulses from the retina only have the small privilege of "setting the clock"

If it is true that...

The organism runs according to a genetically determined "clock" located in certain cells in a specific area of the brain

and

Nervous impulses from the retina only have the small privilege of "setting the clock"

Then it must be true that...

The absence of bright light can create a progesterone deficiency and leave estrogen and prolactin unopposed