As far as the less hours of light thing goes it's difficult to tell, exactly, due to other environmental factors, BUT...
In my last two germination cycles I went from a high male count to a high female count. The 2 things that were different were my lighting schedule and genetics.
I rarely grow the same genetics twice, so I'll leave this part out of the equation, but, it very well could be a deciding factor in regular (not feminized) seeds.
My lighting (6500K T5s ONLY), however, went from the standard 18/6 (high males)to this 12/1 schedule I'm now using (high females). I can't say with any confidence that lighting IS the cause of the higher female counts but it seems to have made a difference at this point in time. I'll know more over the next couple years as I germinate more seeds under this, new to me, lighting schedule.
Sex, in cannabis, is not 100% predetermined by genetics. The proof, IMO, is hermaphrodism and nearly any cannabis plants ability to go into survival mode and change sex/throw nanners. It is a truly rare thing to find a female cannabis plant that refuses to throw nanners, IMO.
farmergiles said:
The environment when the plants are young seems to make a difference to the m/f ratio.
do a search for "epigenetics" for your answer chris.