Researchers from the University of Leicester in the UK have identified nearly 80 genes that are linked to a preference for either 'morningness' or 'eveningness' in flies (
Drosophila melanogaster) - most of these genes can also be found in mammals, too.
You'd think that these genes are directly related to the species "biological clock", but instead they are involved in a range of molecular pathways. These molecular processes aren't just delayed in the 'night owl' flies - they were entirely different.
One research referred to this behaviour as the 'pinball theory' in the sense that "Once a gene expression is delayed, a completely different cascade of molecular events is carried, similar to the ball in a pinball machine that takes a different route in each run. The end point might be similar, but the different molecular routes result in a different journey time."
Source: http://journal.frontiersin.org/article/10.3389/fneur.2015.00100
