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"It is interesting to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, and with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us." (Darwin, 1859)
To illuminate the laws that produce Darwin’s “tangled bank” remains one of biology’s grand challenges, one that requires understanding how differences among forms are selected for and how interdependence among forms is enforced. In natural environments, meeting this challenge is complicated by the fact that selection pressures often vary widely over space and through time. Laboratory evolution experiments with microbial populations offer an attractive alternative by which to study, under controlled conditions, both the dynamic interplay between genotype and phenotype, and the interactions among phenotypes in simple communities. Indeed, because the principal actors in the first 3 billion years of life’s drama were exclusively microbes, we are obliged to use these forms to unlock the secrets of Life’s transitions from simple autocatalytic units to self-organizing, self-replicating, energy transduction systems that range in complexity from single cells to ecosystems. Our team is responding to NAI CAN-7 with a multidisciplinary proposal to address, using experimental and comparative evolutionary genomics, this overarching question: What forces bring about major transitions in the evolution of biocomplexity? Our program of study aims to meet the grand challenge of illuminating and interpreting the laws that produce the “tangled bank” so that we may better understand and appreciate the “grandeur in this view of life.”
The “laws” originally inferred by Darwin were those that give rise to natural selection, which is a consequence of natural variation, inheritance of variation, and the differential reproduction and survivorship of variants according to their fitness. One hundred and fifty years later we now recognize the importance of other factors, in particular chance, whether in the form of genetic drift or historical contingency. Although our knowledge of the mechanism of inheritance is much greater than that of Darwin, it continues to be refined by new insights into what constitutes a gene, how genes interact and how mutation rate itself is subject to natural selection. Significantly, many of these new insights have been opened up by genomics and revealed by members of this team.
Darwin’s grand view was one in which the competitive “Struggle for Life” figured prominently, and indeed, the metaphor of “nature red in tooth and claw” still looms large in the imagination of laymen and scientists alike. However, for decades now it has been recognized that not just competitive but also cooperative interactions are fundamental features of biological systems ranging from enzymes to organelles, cells and societies of cells and organisms.
Our Astrobiology Institute will be organized around five questions related to major transitions in the history of life:
- How do enzymes and metabolic networks evolve?
- How can stress increase biocomplexity?
- How do symbioses arise?
- How does multicellularity evolve?
- How do gene interactions and mutation rate variation constrain evolution of novel traits?
A unifying theme underlying these questions is: how do cooperative vs. competitive interactions play out in driving major transitions that occur when independently replicating entities combine into a larger, more complex whole? We seek general principles that are likely to hold wherever life exists and to collectively affect its degree of complexity. Seeking the answers to these questions falls squarely within Astrobiology, which is the study of the origins, evolution, distribution, and future of life in the universe, and helps to address the first of our discipline’s three principal questions: How does life begin and evolve?