Graduate School of Frontier Sciences, The University of Tokyo Department of
Integrated Biosciences

Extant hominin (humans, Homo sapiens) originated as a species of genus Homo about 200 thousand years ago in Africa and dispersed “Out of Africa” about 50 thousand years ago to most of the lands in the globe. This is contrasting to our closest relatives, great apes, who are still restricted to live in tropical forests. Considering evolutionary time scale, it is surprising that humans attained phenotypic differentiation from great apes in only about 6 million years and further continued it among many local groups (Africans, Europeans, Asians, and many more ethnic groups in each and in between) in only about 50 thousand years. While dispersing from forests to savanna to diverse places with various climatic and landscape conditions, humans have experienced radical changes of lifestyle, such as hunting-gathering to agriculture, free-ranging to settlement, a small community to a big city, simple stone tools to complicated technologies. Our lab studies the origin, process, and genomic underpinning of such human phenotypic differentiation and diversification and evolutionary background behind it as humans being primates, mammals, vertebrates, and so on. We particularly focus on 1) sensory and 2) metabolism adaptation.

Sensory systems interface and monitor outer environments. How have sensory systems adapted to the changing habitat and lifestyle in human evolution? We focus on sensors of color vision (opsins) and chemical senses such as olfaction (ORs), umami/sweet (TAS1Rs) and bitter (TAS2Rs) tastes of which the genes are well studied, and their functional assay methods are well developed. We study not only diverse human ethnic groups but also nonhuman primates as references and models. We attend to comparative study of monkeys of Americas and African/Asian monkeys/apes. Tarsiers, lemurs and lorises, the most distant primates from humans, are also important to examine because they could tell us what the ancestral state of primate senses was and what we have lost and gained from the ancestral state. We also go further into fish, such as stickleback, tetras, zebrafish, medaka and guppy to study their opsin genes as a model system to understand evolutionary flexibility of color vision to diverse light environments. We take multi-disciplinary approaches including genomics, population genetics, molecular evolution, functional assays of sensory receptors using cultured cells, field works in Central-South America and Africa, and biochemical assays of odorants.

Lifestyle-related diseases, such as obesity, are common in modern humans and can be considered phenotypic diversity as skin color and height. Susceptibility to lifestyle-related diseases is influenced by a combination of environmental and genetic factors. The genetic polymorphisms that govern this susceptibility may have been shaped by adaptations during the evolutionary history of our species. Humans can maintain body temperature by metabolically producing heat even when the ambient temperature considerably drops. This heat-producing function is thought to have been essential for our ancestors to adapt to cold environments. Furthermore, this function is expected to prevent obesity in modern society because it uses the fat stored in the body as an energy source. We have found evidence that genetic polymorphisms involved in both the heat-producing function and susceptibility to obesity were adaptive in the ancient human populations living in cold regions. On the other hand, this heat-producing function is also associated with energy wastage, which may have been counter-intuitive and maladaptive in lesser cold but more severe hunger. To clarify the natural selection on human energy metabolism systems and the origin of lifestyle-related diseases, we are studying genetic polymorphisms that link adaptation to cold and starvation with susceptibility to lifestyle-related diseases in modern humans using various approaches.