The N=2 of Life

Lana Sinapayen

We humans only know one example of Life: all known organisms on Earth are thought to be the descendants of one species. One origin of Life. As scientists, we must find this extremely vexing: a science with a sample size of N=1 is only exploring an extremely limited area of the space of possibles. We could sequence the genome of every known organism in the past and present, learn everything about how DNA and environment lead to an organism’s behavior, and still only know but a fraction of what Life is really possible. What unfathomable variations of Life make up the rest of the space of possibles?

We might find the N=2 of Life in 3 ways:
1.Detecting it elsewhere in the universe,
2.Discovering it right here on Earth
3.Building and evolving it in a computer simulation.

Where will we first find N=2?

Astrobiology looks for measures that would help with the first endeavor. I am especially focused on “agnostic biosignatures”, clues that life exists in a region of space (“biosignature”) and that are independent of the type of life (“agnostic”).

It is excessively unlikely that Life on Earth succeeded at its first try. More plausible is the idea that it took several attempts across time and physical space before at least one early form of Life managed to multiply at a scale that protected it from complete extinction.
What about the other attempts? They might have all become extinct, or some could have survived to this day; it is even possible that, in present times, new early forms of Life are continuing to regularly emerge and disappear.
If any of those “other Lifes” were currently around, how would we detect them? If looking for Life in space is like looking for a needle in a haystack, detecting this “Shadow Biosphere” might be more like looking for a needle in a stack of pins.

In both the case of space biosignatures and the case of shadow biosignatures, we cannot rely on assumptions based on the Life we know: this would only allow us to detect organisms that are similar to the ones we know. While those discoveries would still be tremendously exciting, their impact on our understanding of what is possible would be limited. That is why I am much more interested in unconventional definitions of Life that have fewer assumptions than usual. There is no consensus across scientific fields about a single definition of Life. Many definitions are given as a list of rules that a system must satisfy to be considered alive, but all such rules turn out to have exceptions. “Life” is a radial category, with a number of conditions that might or might not be satisfied by actual living organisms. Given the number of known exceptions, the existence of a number of unknown exceptions would not be that surprising. Computer simulations are a good tool to explore exotic scenarios and, to an extent, separate the possible from the impossible.

Artificial Life is a scientific field focused on understanding the principles governing living organisms, by emulating those principles in artificial substrates. Those substrates can be physical, chemical, or even biological and cultural, and of course they can also be computer generated. In this part of my research, I simulate groups of organisms that follow some of the rules of Life while being free from others. While the field of Artificial Life as a whole has not yet produced an artificial system broadly recognized as “alive”, even the pure emulation of an existing organism would provide us with a springboard to test more divergent forms of Life.

So where will N=2 be first detected? In space? Right here on Earth, in a deep ocean or under a rock in someone’s garden? Or in a computer? My personal belief is that if we are unable to define even existing Life in a way that allows us to replicate it artificially, if we are unable to even say whether other types of Life exist on Earth or not, finding Life in space seems almost impossible. But given all these unknowns, it is asserting that there is just one Life in the whole universe that appears to be a leap of faith.