A genomic study of Puerto Rico's Africanized honey bees - which are more docile than other so-called "killer bees" - reveals that they retain most of the genetic traits of their African honey bee ancestors, but that a few regions of their DNA have become more like those of European honey bees. According to the researchers, these changes likely contributed to the bees' rapid evolution toward gentleness in Puerto Rico, a change that occurred within 30 years.