Horizontal Gene Transfer (HGT)—the movement of genetic material between unicellular or multicellular organisms other than by the transmission of DNA from parent to offspring—has long been recognized as a primary driver of evolution in bacteria. Recently, however, researchers have found evidence of HGT in eukaryotes, including plants and animals. For example, certain species of whiteflies have acquired a plant gene that allows them to neutralize toxins produced by the plants they eat. This discovery suggests that HGT may be a more significant factor in eukaryotic evolution than previously thought, providing a shortcut for acquiring complex traits that would otherwise take millions of years to develop through random mutation. Some evolutionary biologists warn that while HGT can be beneficial, it also complicates our ability to reconstruct the tree of life, as genetic lineages can cross and merge in ways that traditional models of vertical descent cannot account for.