Discover how scientists blend biology, synthetic biology, and astrobiology to speculate on alien life forms, focusing on the shared characteristics that might transcend Earth’s biosphere.
One of the biggest challenges in astrobiology — the study of life in the universe — is understanding the very nature of life itself. For over a century, biologists have recognized that life on Earth is built from essential components like DNA, RNA, and amino acids. Fossil records further reveal that life has followed numerous evolutionary paths, giving rise to a vast diversity of organisms. Yet, evidence also suggests that evolutionary possibilities are not endless; convergence and constraints significantly shape and limit the forms life can take.
Exploring Extraterrestrial Possibilities
This raises intriguing questions for astrobiologists: What might life look like on other planets? Can our knowledge of Earth’s biology help us predict alien life? A team of researchers led by the Santa Fe Institute (SFI) explored these questions in a recent study. By examining case studies from various scientific disciplines, they determined that certain fundamental constraints make some forms of life unlikely to exist.
The research team was led by Ricard Solé, the head of the ICREA-Complex Systems Lab at the Universitat Pompeu Fabra and an External Professor at the Santa Fe Institute (SFI). He was joined by multiple SFI colleagues and researchers from the Institute of Biology at the University of Graz, the Complex Multilayer Networks Lab, the Padua Center for Network Medicine (PCNM), Umeå University, the Massachusetts Institute of Technology (MIT), the Georgia Institute of Technology, the Tokyo Institute of Technology, and the European Centre for Living Technology (ECLT).
The Interstellar Probe Scenario
The team considered what an interstellar probe might find if it landed on an exoplanet and began looking for signs of life. How might such a mission recognize life that evolved in a biosphere different from what exists here on Earth? Assuming physical and chemical pre-conditions are required for life to emerge, the odds would likely be much greater. However, the issue becomes far more complex when one looks beyond evolutionary biology and astrobiology to consider synthetic biology and bioengineering.
Challenges in Detecting and Defining Life
According to Solé and his team, all of these considerations (taken together) come down to one question: can scientists predict what possible living forms of organization exist beyond what we know from Earth’s biosphere? Between not knowing what to look for and the challenge of synthetic biology, said Solé, this presents a major challenge for astrobiologists:
“The big issue is the detection of biosignatures. Detecting exoplanet atmospheres with the proper resolution is becoming a reality and will improve over the following decades. But how do we define a solid criterion to say that a measured chemical composition is connected to life?
“[Synthetic biology] will be a parallel thread in this adventure. Synthetic life can provide profound clues on what to expect and how likely it is under given conditions. To us, synthetic biology is a powerful way to interrogate nature about the possible.”
The Cross-Disciplinary Approach to Understanding Life
To investigate these fundamental questions, the team considered case studies from thermodynamics, computation, genetics, cellular development, brain science, ecology, and evolution. They also consider previous research attempting to model evolution based on convergent evolution (different species independently evolve similar traits or behaviors), natural selection, and the limits imposed by a biosphere. From this, said Solé, they identified certain requirements that all lifeforms exhibit:
“We have looked at the most fundamental level: the logic of life across sales, given several informational, physical, and chemical boundaries that seem to be inescapable. Cells as fundamental units, for example, seem to be an expected attractor in terms of structure: vesicles and micelles are automatically formed and allow for the emergence of discrete units.”
Insights from Historical Predictions and Future Predictions
The authors also point to historical examples where people predicted some complex features of life that biologists later confirmed. A major example is Erwin Schrödinger’s 1944 book What is Life? in which he predicted that genetic material is an aperiodic crystal—a non-repeating structure that still has a precise arrangement—that encodes information that guides the development of an organism. This proposal inspired James Watson and Francis Crick to conduct research that would lead them to discover the structure of DNA in 1953.
However, said Solé, there is also the work of John von Neumann that was years ahead of the molecular biology revolution. He and his team refer to von Neumann’s “universal constructor” concept, a model for a self-replicating machine based on the logic of cellular life and reproduction. “Life could, in principle, adopt very diverse configurations, but we claim that all life forms will share some inevitable features, such as linear information polymers or the presence of parasites,” Solé summarized.
Conclusion: The Ongoing Journey of Astrobiology
In the meantime, he added, much needs to be done before astrobiology can confidently predict what forms life could take in our Universe:
“We propose a set of case studies that cover a broad range of life complexity properties. This provides a well-defined road map to developing the fundamentals. In some cases, such as the inevitability of parasites, the observation is enormously strong, and we have some intuitions about why this happens, but not yet a theoretical argument that is universal. Developing and proving these ideas will require novel connections among diverse fields, from computation and synthetic biology to ecology and evolution.”
The team’s paper, “Fundamental constraints to the logic of living systems,” appeared in Interface Focus (a Royal Society publication).
Adapted from an article originally published on Universe Today.
Reference: “Fundamental constraints to the logic of living systems” by Ricard Solé, Christopher P. Kempes, Bernat Corominas-Murtra, Manlio De Domenico, Artemy Kolchinsky, Michael Lachmann, Eric Libby, Serguei Saavedra, Eric Smith and David Wolpert, 25 October 2024, Interface Focus.
DOI: 10.1098/rsfs.2024.0010
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