Atavistic form is a historical approach used to explain criminal behaviour, which is based on the biological factors. This explanation was proposed by Lombroso in the 1870s and suggests that some people are born with a criminal personality (e.g. it is innate) that is a throwback to a previous more primitive ancestor. This was based on research that examined the features and measurements of nearly 4,000 criminals, as well as the skulls of 400 dead criminals. Lombroso found that the criminals examined shared a number of common physical characteristics (e.g. sloping brow, pronounced jaw, high cheekbones, large ears) and concluded that these indicated that such people were more primitive in an evolutionary sense. He also said that such individuals were not responsible for their actions, as they could not be blamed for their innate, inherited physiology.