The Genetics study focused on bees: specifically, the gene that renders worker bees sterile. In evolutionary terms, reproduction is everything, and an animal that cannot reproduce might as well have never lived at all. A gene that causes infertility, the study says, could only have evolved if genes are selfish, as a sterile bee increases the chances of its fertile sister bees passing on their shared genetic material at the expense of ever reproducing itself. By helping the hive as a whole to pass on its genes in general, the sterile bees make the ultimate evolutionary sacrifice, in service to their genes.