Negrescence is a word with a Latin origin and describes "a process of becoming black". It can also refer to having a dark complexion.
In 1885, John Beddoe compiled an index of negrescence to analyze the population of the British Isles. Beddoe used the physical descriptions of a population of 13,000 males to compile his index. He gave one point to a male with red or blonde hair. He gave one point to men with dark hair as well. A black haired male was given two points. If the male had brown or chestnut colored, hair, they were considered neutral. He created a "Map Showing Distribution of Negrescence in Britain". This map was recreated and published by R. H. Hodgkin in 1935. It shows that the hair color of men in western Scotland, Wales and Ireland was darker than the hair color of males in eastern England and eastern Scotland.
This analysis was used to support Beddoe's theory that the Irish had the physical characteristics of the indigenous, aboriginal people of the British Isles.
Professor William E. Cross, Jr. of the City University of New York's Graduate Center included a "theory of Nigrescence" in his groundbreaking book Shades of Black: Diversity in African American Identity published in 1991.