My book How We Do It: The Evolution and Future of Human Reproduction was released by Basic Books on June 11, 2013. In connection with the book, I recently started a regular monthly blog with Psychology Today.
In the tree of life, human evolution is a very unusual case in many ways. If the focus of study is too narrow, it is difficult to avoid special pleading. My long-term research strategy has hence been rooted in the conviction that a wide-ranging approach is essential to identify reliable general principles. Secure interpretation of our biological origins demands comprehensive study of primate evolution from its earliest beginnings. In this spirit, I have conducted sweeping comparisons across primates, covering anatomy of both living and fossil representatives, ecology, behaviour, reproduction and molecular evolution. Study of size relationships (allometric scaling) has been a pervasive theme. A synthetic approach to primate evolution has several benefits. In addition to generating sound general principles, it can reveal relationships that otherwise escape detection. One illustrative example is provided by the endeavour to determine times of divergence in the primate tree, notably the split between humans and chimpanzees. Because of major gaps in the fossil record, estimation of divergence times from earliest known fossil relatives can be seriously misleading. Statistical analysis of the numbers of living and fossil primates in combination with an evolutionary tree based on DNA evidence reveals that divergence times within the primate tree are generally substantially earlier than has often been claimed. In particular, the divergence between humans and chimpanzees — widely held to be around 5 million years ago — in fact appears to be closer to 8 million years ago. Another good example is provided by the close connection between brain size and reproductive biology. Only by examining these features in tandem was it possible to infer that maternal energy resources played a vital part in the evolution of the brain. The "Maternal Energy Hypothesis" is particularly relevant to interpreting the evolution of our own very large brain since we diverged from chimpanzees.
Biographical Sketch:
Several continuing themes in my research originated with my PhD project (1964-67) on behaviour 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 my initial aim was to study their behaviour as a model for inferring adaptations of the earliest primates. While breeding tree-shrews, I discovered a very unusual pattern of maternal behaviour: 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 my long-lasting interest in reproductive biology (particularly maternal behaviour) 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 me 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 I initiated comparative studies of the brain that in turn revealed the pervasive importance of allometric scaling. In my PhD thesis, I 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 my PhD, I 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). I made detailed studies of reproductive biology on their unique breeding colony of mouse lemurs while continuing my broad-based work on primate morphology. During this postdoctoral period, with support from the Royal Society (London), I also conducted my first behavioural/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.
My postdoctoral research was followed by my first university post as Lecturer in Biological Anthropology at University College London (1969-74). In this new post, I 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. I also conducted a second field study of mouse lemurs in Madagascar (1970). During this period at UCL, my interest in allometric scaling grew and I focused in particular on the size of the brain and its parts. My 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 my career, I moved to become Senior Research Fellow at the Wellcome Laboratories, Zoological Society of London (1974-78), where I 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, I 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 behaviour unaffected by sample collection. While applying this to gorillas, I 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). My connection with JWPT (now re-named as the Durrell Wildlife Conservation Trust) strengthened a growing interest in primate conservation biology and led me to focus on the topic of breeding endangered species in captivity.
In 1975, I also spent a semester at Yale University as Visiting Professor in the Department of Anthropology. This allowed me to visit several research centres and museums in the USA to study fossil specimens and develop my 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, I also organised a quantitative radiotelemetric field study of behaviour and ecology of lesser bushbabies in South Africa supported by the Royal Society (1975-77). The fieldwork was mainly conducted by S. Bearder, although I was able to join him for several months in the field. Apart from yielding detailed data on social organization, our observations confirmed my interpretation of the ancestral primate as a small-bodied nocturnal form occupying the fine-branch niche.
From the Zoological Society, I then moved back to University College London for eight years, first as Reader (1978-82) and then as Professor (1982-86) in Biological Anthropology. My 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 my 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, I 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. My interests in fieldwork on primate ecology also continued on a more modest scale during my 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, I was invited to spend 2 months as Senior Visiting Fellow at the Smithsonian Tropical Research Institute, Panama, where I mainly conducted observations on behaviour and ecology of howler monkeys.
In 1986, I 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 behaviour and reproduction. Major collections of primate specimens are also available for quantitative studies. After moving to Zurich, I completed work on an advanced textbook, Primate Origins and Evolution (1990), as a synthetic overview arising from my 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, I later coedited the award-winning Cambridge Encyclopedia of Human Evolution (1993). For the last eight years of my appointment in Zurich, I was a member of the national committee for biology and medicine of the Swiss National Science Foundation.
In September 2001, I took up an appointment at The Field Museum, first as Vice President and then as Provost for Academic Affairs. My responsibilities, with an emphasis on external relationships, were to coordinate research programmes, 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 my administrative appointment, I held a post as curator in Anthropology. After stepping down from my administrative role as Provost in 2006, I became the A. Watson Armour III Curator of Biological Anthropology and have since been able to devote my energies predominantly to research, teaching and publication.
