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With Darwin's information Lombroso began to apply the research of other scholars. Lombroso studied the works of Francis Galton and his thinking on human heredity. Galton believed that over many years a subject's character and talents would revert to that of the average population. He used the average as a means of measuring the intellectual and mediocrity of the population. Galton wanted to understand the workings of human hereditary processes to see if he could tamper with them to increase the good traits over the bad. .
With the information gathered from both subjects Lombroso began a study of his own. Lombroso began studying the bodies of renowned criminals unlike the studies conducted by the criminologist who believed in the classical school. Lombroso examinations of his subjects matched the bodies to his theories. Measuring the heads of the living and executed criminals against the skulls of apes and prehistoric humans to what he considered as primitive people. This research was based much information and on many factors, from epilepsy to the circumference of the brain. With this information he developed the theory of the born criminal. One group of people he studies he named the atavist. These so called atavist were throwbacks to primitive man and this was the cause for there criminal behavior. The atavist theory rejected Darwin's theory of evolution to a degree by implying that while most people evolve, some devolve becoming primitive. Additional he noted that there were physical marks and or characteristics that could be an indicator that an individual was atavistic. These marks were called stigmata and they were abnormal skulls sizes, hawk like noses, large jaws and cheek bones, and fleshy lips. .
His research indicated that the crimes that were being committed by these individuals, was due to their biological makeup, beyond the control of the individual. Lombroso concluded that in any population, there are a small percentage of people that were likely to exhibit primitive instincts.