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Introduction

Research of the MIT team focuses on the environmental, ecological and genetic factors that lead to the evolution of complex life. On Earth, at least 30 different lineages have achieved some level of multicellularity. But organisms with differentiated cells have evolved only six times: fungi; red algae; brown algae; twice in the green algae, including plants; and animals. How such complexity arose is a compelling issue for the NASA Astrobiology Institute for several reasons:

1. Our first indication of life beyond earth is likely to come from the atmospheric composition of an extra-solar planet. Interpreting these results will require understanding how atmospheres evolve in response to complex life. This increases the importance of understanding the history of Earth’s atmosphere and how it has evolved in response to life, particularly complex life.
2. By probing temporal and developmental relationships between environmental, genetic and ecological factors associated with the evolution of complex life on Earth, we can productively examine global metabolism.
3. The spatial and environmental distributions of complex, multicellular organisms are much more restricted than those of microorganisms. Accordingly, multicellular organisms are more sensitive indicators of the relative importance of environmental, genetic/developmental, and ecological factors in the origin and establishment of evolutionary novelties.

The MIT team’s unifying intellectual focus on the requirements for development and evolution of complex multicellularity is motivated by such questions as: What combination of genetic, environmental and ecological factors led to the emergence of complex multicellularity on Earth? What conditions allow a planet to become habitable by complex organisms? What genetic and developmental innovations were required to assemble complex organisms? How were the new niches constructed? We will pursue these questions under the following five themes:

1. Molecular paleobiology: We employ studies of biomarkers, the role of O2 in sterol biosynthesis, genomic and phylogenetic studies to elucidate the context of early eumetazoan evolution, relationships to unicellular ancestors, and the development of the gut and sensory systems.
2. Metabolic networks from single cells to ecosystems: We investigate environment and ecosystem-dependent metabolic transitions important for the development of multicellularity and the impact of O2 on biochemical networks and trophic structures.
3. Global metabolism: We are developing new geological and geochemical datasets to asses the controls on, and responses to, rising oceanic and atmospheric pO2 and the transitions between the major redox stages of Earth history.
4. Field Investigations: We are investigating the environmental context of early animal and plant evolution, through geological, paleontological and geochronologic studies of rocks in Oman, China, Namibia, Spain and Australia.
5. Astrobiological Exploration: we are studying Earth analogs for Martian environments of astrobiological interest and model the evolution of Earth’s albedo as a function of the advance of multicellular life.