Sergi's initial contribution was to oppose the use of the
cephalic index to model population ancestry, arguing that over all
cranial morphology was more useful. However, Sergi's major theoretical achievement was his model of human ancestry, fully articulated in his books
Human Variation () and
The Mediterranean Race (1901), in which he argued that the earliest European peoples arose from original populations in the
Horn of Africa, and were related to
Hamitic peoples. This primal "Eurafrican race" split into three main groups, the
Hamites, the
Mediterranean race and the north European
Nordic race. Semitic people were closely related to Mediterraneans but constituted a distinct "Afroasian" group. The four great branches of the Mediterranean stock were the
Libyans or
Berbers, the
Ligurians, the
Pelasgians and the
Iberians.
Ancient Egyptians were considered by Sergi as a branch of the Hamitic race. According to Sergi the Mediterranean race, the "greatest race in the world", was responsible for the great civilisations of ancient times, including those of
Egypt,
Carthage,
Greece and
Rome. These Mediterranean peoples were quite distinct from the peoples of northern Europe. Sergi argued that the Mediterraneans were more creative and imaginative than other peoples, which explained their ancient cultural and intellectual achievements, but that they were by nature volatile and unstable. In his book
The Decline of the Latin Nations he argued that Northern Europeans had developed stoicism, tenacity and self-discipline due to the cold climate, and so were better adapted to succeed in modern civic cultures and economies.
Anti-Nordicism These theories were developed in opposition to
Nordicism, the claim that the Nordic race was of pure
Aryan stock and naturally superior to other Europeans. Sergi ridiculed Nordicists who claimed that the leading Greeks and Romans were of Nordic background and argued that the Germanic invasions at the end of the Roman Empire had produced "delinquency, vagabondage and ferocity". Sergi believed that the Aryans were originally "Eurasiatic" barbarians who migrated from the
Hindu Kush into Europe. He argued that the Italians had originally spoken a
Hamitic language until the Aryan (
Indo-European)
Italic language spread across the country. Some Aryan influence was detectable in Northern Italy, but, racially speaking, Italians were unaffected by Aryan migrants. Sergi expanded on those theories in later publications. Despite his denigration of Aryans and emphasis on Mediterranean racial identity, he denied that he was motivated by national pride, asserting that his works had the "goal of establishing the veracity of the facts without racial prejudice, without diminishing the value of one human type in order to exalt another one." His last book,
The Britons (1936), sought to trace the rise of the
British Empire to the Mediterranean component of the British population. ==Theory of emotions==