Most research on the origins of life on Earth assumes a single initiating event some four billion years ago. Debate rages as to the form and location of life's origins – but what if life evolved several times, resulting in the diversity around us? The possibility has been raised in a paper published in the Journal of Molecular Evolution, along with some of the implications that might stem from taking the idea seriously.
Professor Chris Kempes and Professor David Krakauer of the Sante Fe Institute think we need to consider what is really meant by life and its origins. This question is already touched on in discussions about whether things like viruses and prions are actually alive, but Kempes and Krakauer want to look at it more broadly still.
The authors argue that most scientists have focused too much on the individual organism, ignoring the ecosystem on which it depends. However, if a virus is considered not to be alive because it cannot replicate without a cell to take control of, what does that say about other organisms that can't live without the conditions that support them, such as obligate parasites?
Perhaps, Kempes and Krakauer suggest, we should see life/non-life as a spectrum rather than a binary division.
Within this framework, certain developments may be seen as; “A new form of life, not just an adaptation,” Krakauer said in a statement.
Kempes added; “Human culture lives on the material of minds, much like multicellular organisms live on the material of single-celled organisms.” On this basis, complex ecosystems like forests or coral reefs could be seen as new forms of life, rather than ways for existing life to organize itself.
“Like all information-processing systems, adaptive systems possess a nested hierarchy of levels, a level of function optimization (e.g., fitness maximization), a level of constraints (e.g., energy requirements), and a level of materials (e.g., DNA or RNA genome and cells),” the paper notes.
Even when it comes to more traditional definitions of life, the authors point to a previous paper that they say "convincingly" suggested; “There could be many paths from an abiotic to biotic Earth with various potential bottlenecks, convergences, and branching points.”
This is in contrast to a more traditional view of life as similar to a fire, with a single ignition point that was passed on, potentially spreading and dying back but never being completely extinguished.
Considering the meaning (or, at least, definition) of life in this way could be important if we want to find it beyond the Earth. As the paper asks; “How can we be sure that we have found life if it is materially different from life on Earth, and by extension, how do we verify that an environment is truly lifeless, for example, in a sample of ice from Enceladus?” could also make us think more broadly about; “The range of possibilities for the origin and maintenance of life.”