Hutus and Tutsis are the two main ethnic groups in Rwanda. They are most known in the West because of their roles in the Rwandan genocide of 1994, in which Hutu extremists massacred more than 800,000 Tutsis and Hutu moderates. It is believed that the differences in skin tone can determine whether a person is Hutu or Tutsi. However, because the races regularly mixed, this is not a reliable guide.
Tutsis are typically thought of as lighter skinned than those of Hutu decent. Many descriptions of Tutsis include that they have light brown skin like Ethiopians, Eritreans and other ethnic groups from farther north in Africa. Many scholars believe Tutsis are a separate ethnic group that migrated to Rwanda, most likely from the North. Once they settled in Rwanda, however, Tutsis and Hutus regularly mixed, and the names "Hutu" and "Tutsi" became shorthand for social class as much as ethnic background. Hutus who moved into dominant positions in society (positions usually occupied by the Tutsi elite) were considered to be Tutsis, while Tutsis who settled down to farm were considered to be Hutus. The modern understanding of Tutsis as purely light skinned is also deeply rooted in racist colonial doctrines that sought to justify the Tutsi dominance of Rwanda on the grounds of their greater "whiteness." In modern Rwanda, it is not possible to reliably tell someone's Tutsi background from their skin tone.
The Hutu, as a settled group that existed in Rwanda before the arrival of the Tutsi, are generally considered to be darker skinned, with tones resembling the very dark browns of other Central Africans. Just as with Tutsis, this characteristic is not a reliable guide to the ethnic origin of any individual Rwandan, but it may reflect some residual genetics from a time before the arrival of the Tutsi in the area.
Anthropologists have come up with long lists of characteristics dividing Hutu and Tutsi. All of them are subject to serious academic debate. Broadly speaking, Tutsis are said to have higher cheekbones, larger skulls and longer necks than Hutus. There may also be genetic differences. Some studies have found that there are a lower proportion of people with sickle cell anemia among the Tutsis. Since this protects from malaria, the presence of a sickle cell gene usually indicates that a group has lived in a malarial area for some time. This would suggest that the Hutu arrived from a less-malarial area within their recent history.