In a new study published on Thursday in the journal PLOS Genetics, researchers used artificially bred fruit flies to examine the role of genes in the sleep process, reports Newsweek.

“This study is an important step toward solving one of the biggest mysteries in biology: the need to sleep,” lead study author Susan Harbison, an investigator in the Laboratory of Systems Genetics at the National Heart, Lung, and Blood Institute (NHLBI), said in a statement. “The involvement of highly diverse biological processes in sleep duration may help explain why the purpose of sleep has been so elusive.”

Harbison and her colleagues analyzed 13 generations of wild fruit flies—some of which they bred to sleep up to 18 hours each day, while others were bred to sleep only three hours each day. When the researchers examined genetic data among the two groups, they found 126 variations in 80 candidate genes that researchers believe are associated with sleep.