Racial groups and human species
As a proponent of polygenism, Broca rejected the monogenistic approach that all humans have a common ancestor. Instead he viewed human racial groups as coming from different origins. Like most of the proponents on either side, he viewed each racial group as having a place on a 'barbarism' to 'civilization' progression. He saw European colonization of other territories as justified by its being an attempt to civilize the barbaric populations. In his 1859 work On the Phenomenon of Hybridity in the Genus Homo, he argued that it was reasonable to view humanity as composed of independent racial groups – such as Australian, Caucasian, Mongolian, Malayan, Ethiopian, and American. He saw each racial group as its own species, connected to a geographic location. All together, these different species were part of the single genus homo. Per the standard of the time, Broca would also refer to the Caucasian racial group as white, and to the Ethiopian racial group as Negro. In his writings, Broca's use of the word race was narrower than how it is used today. Broca considered Celts, Gauls, Greeks, Persians and Arabs to be distinct races that were part of the Caucasian racial group. Races within each group had specific physical characteristics that distinguished them from other racial groups. Like his work in anatomy, Broca emphasized that his conclusions rested on empirical evidence, rather than a priori reasoning. He thought that the distinct geographic location of each racial group was one of the main problems with the monogenists argument for common ancestry:There was even, no necessity to insist upon the difficulty, or greater geographical impossibility of the dispersion of so many races proceeding from a common origin, nor to remark that before the remote and the almost recent migrations of Europeans, each natural group of human races occupied upon our planet a region characterized by a special fauna; that no American animal was found either in Australia nor in the ancient continent, and where men of a new type were discovered, there were only found animals belonging to species, then to general, and sometimes to zoological orders, without analogues in other regions of the globe. Broca also felt that there was not enough evidence for the theory that appearance of different races could be changed by the qualities of the environments that they lived in. Broca saw the physical characteristic of Jews being the same as those portrayed in the Egyptian paintings from the 2,500 B.C., even though, by 1850 A.D. that population had spread to different locations with vastly different environments. He pointed out that his opponents were unable to provide similar long-term comparisons.
Broca, influenced by previous work of Samuel George Morton, used the concept of hybridity as his primary argument against monogenism, and that it was flawed to see all of humanity as a single species. Different racial groups' ability to reproduce with each was not sufficient to prove that idea. Under Broca's view on hybridity, the result of a reproduction between two different races could fall into four categories: 1) The resulting offspring are infertile; 2) Where the resulting offspring are infertile when they reproduce between themselves but are sometimes successful when they reproduce with the parent groups; 3) Known as paragenesic, where the offspring's descendants are able reproduce within themselves and with parents, but the success of the reproduction lowers with every generation until it ends; and 4) Known as eugenesic, where a successful reproduction can continue indefinitely, between the intermix descendants and with the parent group.
Looking at historical population figures, Broca concluded that the population of France was an example of a eugenesic mixed race, resulting from intermixing of Cimbri, Celtic, Germanic and Northern races within the Caucasian group. On the other hand, the thought that observations and population data from different regions of Africa, Southeast Asia, and North and South America, showed a significant decrease in physical and intellectual abilities of mixed groups when compared to the different races that they originated from. Concluding that intermixed descendants of different racial groups could only be Paragenesic.I am far from advancing these suppositions as demonstrated truths. I have studied and analysed all documents within my reach; but I cannot be responsible for facts not ascertained by myself, and which are too much in opposition to generally received opinions to be admitted without strict investigation... Until we obtain further particulars we can only reason upon the known facts; but these, it must be admitted, are so numerous and so authentic as to constitute if not a rigorous definitive demonstration, at least a strong presumption of the doctrines of polygenists.
On the Phenomenon of Hybridity was published the same year as Darwin's presentation of the theory of evolution in the On the Origin of Species. At that time, Broca thought of each racial group was independently created by nature. He was against slavery and disturbed by extinction of native populations caused by colonization. Broca thought that monogenism was often used to justify such actions, when it was argued that, if all races were of a single origin then "the lower status of non-Caucasians" was caused by how their race acted following creation. He wrote: The difference of origin by no means implicates the subordination of races. It, on the contrary, implicates the idea that each race of men has originated in a determined region, as it were, as the crown of the fauna of that region; and if it were permitted to guess at the intention of nature, we might be led to suppose that she has assigned a distinct inheritance to each race, because, despite all that has been said of the cosmopolitism of man, the inviolability of the domain of certain races is determined by their climate.
Broca is known for making contributions towards anthropometry—the scientific approach to measurements of human physical features. He developed numerous instruments and data points that were the basis of current methods of medical and archeological craniometry. Specifically, cranial points like glabella and inion and instruments like craniograph and stereograph. Unlike Morton, who believed that a subject's brain size was the main indicator of intelligence, Broca thought that there were other factors that were more important. These included prognathic facial angles, with closer to right angles indicating higher intelligence, and the cephalic index relationship between the brain's length and width, that was directly proportional with intelligence, with the most intelligent European group being 'long headed', while the least intelligent Negro group being 'short headed'. He thought that the most important aspect, was the relative size between the frontal and rear areas of the brain, with Caucasians having a larger frontal area than Negroes. Broca eventually came to the conclusion that larger skulls were not associated with higher intelligence, but still believed brain size was important in some aspects such as social progress, material security, and education. He compared cranial capacity of different types of Parisian skulls. In doing so he found that the average oldest Parisian skull was smaller than a modern, wealthier Parisian skull and that both were bigger than the average skull from a poor Parisian's grave. Aside from his approaches to craniometry, Broca made other contributions to anthropometry, such as developing field work scales and measuring techniques for classifying eye, skin, and hair color, designed to resist water and sunlight damage.
