A Debate: Who Was the Hobbit?

Robert Martin

Several continuing themes in Robert Martin's research originated with his PhD project (1964-67) on behavior and evolution of tree-shrews (Tupaiidae). This was based on research with K. Lorenz and I. Eibl-Eibesfeldt (Max-Planck-Institut, Seewiesen), supervised by N. Tinbergen (University of Oxford). Tree-shrews were then widely thought to be the most primitive living primates and his initial aim was to study their behavior as a model for inferring adaptations of the earliest primates. While breeding tree-shrews, Martin discovered a very unusual pattern of maternal behavior: the infants are kept in a separate nest and the mother suckles them only once every 48 hours during a very brief visit. This finding not only stimulated his long-lasting interest in reproductive biology (particularly maternal behavior) but also revealed a stark contrast with the intensive infant care that typifies primates, suggesting that tree-shrews are not in fact related to them. This led him to re-examine the evidence (largely morphological) for inclusion of tree-shrews in the order Primates. Data on size and structure of the brain had been very influential and so he initiated comparative studies of the brain that in turn revealed the pervasive importance of allometric scaling. In his PhD thesis, Martin concluded that tree-shrews are not close relatives of primates. This conclusion has since been reinforced by several other investigations and tree-shrews are now generally relegated to the separate mammalian order Scandentia. In fact, however, the process of excluding tree-shrews from the order Primates brought the key adaptations of real primates into sharper focus, revealing a very early origin for many key features of human biology. In a recent twist, molecular evidence has indicated that the little-studied colugos (Dermoptera) are the most likely sister group of primates.

Following his PhD, Martin decided to study relatively primitive undoubted primates and obtained a NATO postdoctoral grant (1967-69) to work with J.-J. Petter and A. Petter-Rousseaux (Museum National d'Histoire Naturelle, Brunoy). He made detailed studies of reproductive biology on their unique breeding colony of mouse lemurs while continuing his broad-based work on primate morphology. During this postdoctoral period, with support from the Royal Society (London), Martin also conducted his first behavioral/ecological field study in Madagascar (1968), including original observations on mouse lemurs. Combined field and laboratory observations indicated that mouse lemurs are in fact a suitable model for inferring the ancestral primate condition and that several key adaptations can be traced to a small nocturnal ancestor in the "fine-branch niche" of tropical and subtropical forests.

Martin's postdoctoral research was followed by his first university post as Lecturer in Biological Anthropology at University College London (1969-74). In this new post, Martin continued to work on reproduction of mouse lemurs in a newly founded colony, while simultaneously expanding comparative work on morphology of the skull, brain, postcranial skeleton and reproductive system in primates. He also conducted a second field study of mouse lemurs in Madagascar (1970). During this period at UCL, his interest in allometric scaling grew and he focused in particular on the size of the brain and its parts. Martin's work also expanded to include studies of primate fossils, notably early forms such as Adapis, including study of endocasts of the cranial cavity.

At this point in his career, Martin moved to become Senior Research Fellow at the Wellcome Laboratories, Zoological Society of London (1974-78), where he was responsible for coordinating research on mammalian reproduction. The main projects involved breeding colonies of primates: mouse lemurs, owl monkeys and cottontop tamarins. Owl monkeys are the only nocturnal higher primates and were also of major interest for research on human malaria, so a grant was obtained from the Wellcome Trust to conduct, with A. Dixson, the first detailed study of their reproductive biology. In connection with the projects on primate reproduction, he established a laboratory for hormone radioimmunoassay. This opened up possibilities for conducting hormonal studies on easily-collected urine samples and combining these with studies of behavior unaffected by sample collection. While applying this to gorillas, he initiated a long-standing research connection with the Jersey Wildlife Preservation Trust, becoming Chairman of the Scientific Advisory Committee in 1975 and a Council member in 1978 (both posts held until 2001). His connection with JWPT (now re-named as the Durrell Wildlife Conservation Trust) strengthened a growing interest in primate conservation biology and led him to focus on the topic of breeding endangered species in captivity.

In 1975, Martin also spent a semester at Yale University as Visiting Professor in the Department of Anthropology. This allowed him to visit several research centers and museums in the USA to study fossil specimens and develop his work on comparative morphology. One significant finding confirmed by comparative studies of endocasts of fossil and living primates is that brain size has increased over time in all lineages, so humans are in fact distinguished from other primates by an unusually high rate of brain expansion.


In parallel to other studies, Martin also organized a quantitative radiotelemetric field study of behavior and ecology of lesser bushbabies in South Africa supported by the Royal Society (1975-77). The fieldwork was mainly conducted by S. Bearder, although Martin was able to join him for several months in the field. Apart from yielding detailed data on social organization, their observations confirmed Martin's interpretation of the ancestral primate as a small-bodied nocturnal form occupying the fine-branch niche.

From the Zoological Society, Martin then moved back to University College London for eight years, first as Reader (1978-82) and then as Professor (1982-86) in Biological Anthropology. His primary research became focused on allometric scaling, particularly concerning the brain. A key development was the inference of a link between metabolic rate and brain size in mammals. The realization that this link must be indirect led to his hypothesis, linking brain size to reproductive biology, that resources provided by the mother have a major influence on the evolution of brain size. This "maternal energy hypothesis" was first published in Nature in 1981 and consolidated in the 1982 James Arthur Lecture on the Evolution of the Human Brain (American Museum of Natural History, New York). It also led to a 3-year project grant (1982-85) from the Medical Research Council (London) to investigate quantitative aspects of brain development and associated reproductive features of primates. In 1983, Martin spent a semester as Professeur Associe at the Musee de l'Homme, Paris and used this opportunity to study variation in modern human brain size. Martin's interests in fieldwork on primate ecology also continued on a more modest scale during his second period at UCL. Two study visits were made to Brazil with support from the Royal Society (1980) and the British Council (1982-85). In 1981, Martin was invited to spend 2 months as Senior Visiting Fellow at the Smithsonian Tropical Research Institute, Panama, where he mainly conducted observations on behavior and ecology of howler monkeys.

In 1986, Martin moved to take up the post of Director and Professor at the Anthropological Institute in Zurich and built up a range of research activities. The breeding colony of New World monkeys (Callimico, Callithrix, Cebuella) became an important research resource for work on behavior and reproduction. Major collections of primate specimens are also available for quantitative studies. After moving to Zurich, Martin completed work on an advanced textbook, Primate Origins and Evolution (1990), as a synthetic overview arising from his research. Two chapters cover the sense organs and the brain, which played a pivotal role in primate evolution. Together with S. Bunney, J.S. Jones and D.R. Pilbeam, Martin later coedited the award-winning Cambridge Encyclopedia of Human Evolution (1993). For the last eight years of his appointment in Zurich, Martin was a member of the national committee for biology and medicine of the Swiss National Science Foundation.

In September 2001, Martin took up an appointment at The Field Museum, first as Vice President and then as Provost for Academic Affairs. His responsibilities, with an emphasis on external relationships, were to coordinate research programs, collections management, contributions to higher education and exhibit-related activities with a team of 40 curators and 60 professional staff in Anthropology, Botany, Geology and Zoology. In parallel to his administrative appointment, Martin held a post as curator in Anthropology. After stepping down from his administrative role as Provost in 2006, Martin became the A. Watson Armour III Curator of Biological Anthropology and has since been able to devote his energies predominantly to research, teaching and publication.