His work revealed that the brains of patients with aphasia contained lesions in a particular part of the cortex, in the left frontal region.

Broca's work contributed to the development of physical anthropology, advancing the science of anthropometry,[5] and craniometry, in particular, the now-discredited practice of determining intelligence.

[8] After graduating, Broca undertook an extensive internship, first with the urologist and dermatologist Philippe Ricord (1800–1889) at the Hôpital du Midi, then in 1844 with the psychiatrist François Leuret (1797–1851) at the Bicêtre Hospital.

[19] The Society Anatomique de Paris met every Friday and was chaired by anatomist Jean Cruveilhier, and interned by "the Father of French neurology" Jean-Martin Charcot; both of whom were instrumental in the later discovery of multiple sclerosis.

[20] At its meetings, members would make presentations regarding their scientific findings, which would then be published in the regular bulletin of the society's activities.

[19] He demonstrated that rickets, a disorder that results in weak or soft bones in children, was caused by an interference with ossification due to disruption of nutrition.

[28][n 2] As a surgeon, Broca wrote a detailed review on recently discovered use of chloroform as anesthesia, as well as on his own experiences of using novel pain managing methods during surgery, such as hypnosis and carbon dioxide as a local anesthetics.

[29] Broca used hypnosis during surgical removal of an abscess and received mixed results, as the patient felt pain at the beginning which then went away, and she could not remember anything afterwards.

[n 4] 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.

Broca considered Celts, Gauls, Greeks, Persians and Arabs to be distinct races that were part of the Caucasian racial group.

[44] 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.

[46] 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.

[54] 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.

[55] 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.

[n 7] 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.

[63] Even on a narrower level Broca saw evolution as insufficient explanation for the presence of some traits:Apply Darwin's thinking to the genus Orang (Satyrus) ...

The Darwinists will answer that one day a certain Pithecus was born without a big toe nail, and his descendants have perpetuated this variety ... Let us call this ape ... Prosatyrus I, as it behooves the founder of a dynasty ...

[64]Ultimately, Broca believed that there had to be a process that ran parallel to evolution, to fully explain the origins of, and divergences, between different species.

[66] This area of study began for Broca with the dispute between the proponents of cerebral localization – whose views derived from the phrenology of Franz Joseph Gall – and their opponents led by Pierre Flourens.

However, Gall's former student, Jean-Baptiste Bouillaud, kept the localization of function hypothesis alive (especially with regards to a "language center"), although he rejected much of the remaining phrenological thinking.

[66] Broca's Society of Anthropology of Paris was a place where language was regularly discussed in the context of race and nationality, and it also became a platform for addressing its physiological aspects.

The localization of function controversy became a topic of regular debate when several experts of head and brain anatomy, including Aubertin, joined the society.

[71] He determined that, as predicted, Leborgne did in fact have a lesion in the frontal lobe in one of the cerebral hemispheres, which in this case turned out to be the left.

Although history credits this discovery to Broca, another French neurologist, Marc Dax, had made similar observations a generation earlier.

Based on his work with approximately forty patients and subjects from other papers, Dax presented his findings at an 1836 conference of southern France physicians in Montpellier.

Over 100 years later Nina Dronkers, an American cognitive neuroscientist, obtained permission to re-examine these brains using modern MRI technology.

[79] The brains of many of Broca's aphasic patients are still preserved and available for viewing on a limited basis in the special collections of the Pierre-and-Marie-Curie University (UPMC) in Paris.

[66][70] In 1868 Charles Darwin criticized Broca for believing in the existence of a tailless mutant of the Ceylon junglefowl, described in 1807 by the Dutch aristocrat, zoologist and museum director Coenraad Jacob Temminck.

Comparing then-dominant craniometry-based measures of intelligence, as well as other factors such as relative forearm-to-arm length, he proposed that Negroes were an intermediate form between apes and Europeans.

[55] The evolutionary biologist Stephen Jay Gould criticized Broca and his contemporaries of being engaged in "scientific racism" when conducting their research.