The scientists were able to replicate the gene variation in mice which also needed less sleep.

Maybe it's this enzyme, that vitamin, this hormone influenced by that gene variation, too much or too little.

With very little gene variation within the species, healthy reproduction becomes increasingly difficult, and offspring are more likely to have problems resulting from inbreeding.

Several clock gene variations have been associated with an elevated risk of developing mood disorders.

Gene variations believed to be linked to television viewing are also found in people who are less educated and those with a higher body mass index.