Lyddeker was prospecting the Siwaliks and collecting numerous fossils of vertebrates preserved in the Museum of Calcutta. Among these fossils was a fragment of a monkey’s jawbone collected in 1879. Close to the gibbon, the geologist named it Paleopithecus sivalensis, then in 1886, he described a canine tooth which resembled that of an orangutan. It was the second fossil of a large anthropoid after the mandible of Dryopithecus. Henceforth, the Siwaliks became the cradle of the origin of Man. This perspective was in line with the deductions of Georges Cuvier who thought it was located somewhere in the Himalayan heights, based on paleoclimatic arguments linked to a rise in sea water on a planetary scale. For the high Himalayan peaks, global warming was to result in the melting of the glaciers and the consequent flooding of the plains by the powerful Himalayan rivers.
1.2.1. The Java erect ape-man, or the missing link, Pithecanthropus
Haeckel’s anthropogeny placed the ancestors of the gibbon in the ancestral lineage of Man and predicted a fossil link that he named Pithecanthropus. Since gibbons and orangutans still live in Southeast Asia, Haeckel located the cradle of humanity between Sumatra, Java and Borneo. The probability of finding fossils of this “missing link” in Asia was therefore supported by this maxilla and canine discovered in sub-Himalayan India. Five years later, in 1891, paleoanthropology made a prodigious leap forward in time thanks to a Dutch doctor. Eugène Dubois (1858–1940) had recently defended his thesis in medicine, in 1884, and was soon appointed lecturer with the chair of Anatomy at the University of Amsterdam in 1886. He was neither an anthropologist nor a paleontologist, but he did intend to devote his free time to researching this Pithecanthropus. In 1887, he decided to leave Amsterdam to settle in Sumatra with his family, and joined the Royal Dutch Indian Army as a doctor.
Human paleontology was not yet a discipline; the Neanderthal skeleton and the Gibraltar skull had still not been described. Dubois went to the island of Java and prospected the ancient formations of a river, the Solo, on a paleontological site called Trinil. Between 1891 and 1892 many fossils were collected with the help of two engineers and some convicts. These fossils included two human molars and a human-like skull cap with a low vault and a strong bulge above the orbits. Subsequently, a perfectly preserved femur of modern appearance was collected about 15 m from the area. The skull base was missing and only the proximity justified the association of the femur and the skull cap. Dating went back to the Middle Pleistocene (500,000 years in 2020). Dubois published a description of the fossils in Java in 1894 (Dubois 1894), comparing the skull cap with a chimpanzee and decided to attribute the fossil to an extinct genus of Hominids, the Pithecanthropus, and to add the femur to define the species as erectus, in other words, the erect ape-man. Cranial capacity was estimated at 900 ml, while that of Homo sapiens is 1,350 ml on average, that of the orangutan is 320–340 ml and that of the gibbon is 82 ml (White 2007). On the strength of his discovery, Dubois traveled around Europe in 1895 to obtain the approval of anatomists. The monograph was read carefully by the most informed authorities, some 20 experts, and the conclusions were more in the realm of opinions, ranging from a giant gibbon to an extinct genus of intermediate hominin between Ape and Man. The Société d’Anthropologie de Paris appreciated the discovery and its implications. In January 1895, Léonce Manouvrier (1850–1927), a specialist in the physiology and anatomy of the human brain, presented his analysis and conclusions (Manouvrier 1895). After seeing the originals, he confirmed his position in 1896 and invited Eugène Dubois to come and present his arguments (Manouvrier 1896). The numerous fossils of vertebrates resembled the most recent species of Siwaliks (2 million to more than 700,000 years old).
If the skull cap was that of a hominin, then the date when Man’s ancestors must have appeared would defy theologians. However, the association of the “modern” femur with a skull and a brain both different from that of a Homo sapiens posed a problem. The discussion revolved around bipedalism, within the framework of the doctrine of the locomotor origins of human anatomy. Indeed, for Dubois, who apparently did not compare the femur of a man with that of a gibbon, the latter was also bipedal:
Certainly it was not to be assumed that the femur of an anthropoid becoming bipedal could be very different from a human femur, the function being the same and the form already approximated by the origin. (Dubois, Le Pithecanthropus erectus et l’origine de l’homme, 1896, author’s translation)
Dubois was of course interested in the brain. In 1897, he published a synthesis on the evolution of the central nervous system, which was taken up and translated by Léonce Manouvrier for the Société d’Anthropologie de Paris:
The central nervous system of animals has increased in complexity and volume as their relationships with the external world have multiplied [...]. Mammals have much larger and more sophisticated brains than all other animals and show to some extent, according to the degree of the order to which they belong, an increasing development. They have acquired this superior organization gradually. Marsh1 and others have shown that the brain dimensions in mammals of the Eocene period are generally smaller than in related forms of the Neo-Tertiary or present day. Placental mammals of all orders in the earliest Eocene terrain have extremely small cranial cavities. In animals belonging to one of these orders, the brain was thinner than the spinal cord, so much so that it could have easily been extracted from the skull through the foramen magnum and the vertebral canal. At the same time, Marsh demonstrates that it was mainly the upper organized parts of the brain, the cerebral hemispheres, which were very poorly developed in these oldest placental mammals, with the result that these forms are even less distant, with regards to this point, from reptiles than recent placental mammals. This progressive development of the brain, in organization and volume, in vertebrates and mainly in mammals, as well as the remarkable volume and complexity in structure that it finally reaches in man, demonstrate that in this organ, the development of function determines the complication of structure and quantity as well. (Dubois, Sur le rapport du poids de l’encéphale avec la grandeur du corps chez les mammifères, 1897, author’s translation)
The complexification of the mammalian encephalon was maintained during the Tertiary era and Man was therefore the last degree of complexity:
No animal of the same size has a brain size comparable to that of man. Anthropoid great apes, whose body weight is equal to that of man, do not even reach 1/3, and dogs with the same weight 1/10, with regard to the brain and the weight of a man. Only the elephant, the largest whales and the Rhytine (Rhytina stelleri)2, an animal that disappeared in the last century, outweigh man in terms of the absolute weight of the brain [...]. For animals whose body weight is minimal: the relative weight of the shrew’s brain is 1/23, the monkey lion 1/26, the Javanese Tupaja 1/41, the mustached bat (Vesperttlio mystacinus) 1/42, while the relative weight of the human brain is 1/46 to 1/45: however, among these, in the shrew and the bat, the brain has a much lower organization. (ibid., author’s translation)
Encephalization was therefore not a question of absolute mass, volume, or weight relative to the body, it was a question of organization and the duration of growth:
Not enough attention is paid to the fact that the brain increases less in weight with age than the rest of the body. In humans it has already reached about the same weight as in adults by the ninth year of life, while the body weight increases more than twice as much. The same can be seen, as Dr. Weber demonstrated, in all mammals; the brain has finished growing much earlier than other parts of the body. (ibid., author’s translation)
Eugène Dubois did not accept criticism and did not allow access to the fossils before 1923. He was nevertheless supported by Léonce Manouvrier, not on an anatomical basis as there was a lack of comparative material, but on the significant mineralization and the proximity of other bones. Following that, the Java collections were enriched and supported the case for