If, as we discussed earlier, physics and thus chemistry is deterministic and therefore, in the right circumstances, life is inevitable, is it possible that within that specific chemosystem any life that emerges will use the same chemical pathways and structures as they are the most efficient in that environment. We know that life could have chosen alternatives to some key chemical elements, yet is doesn’t appear to have done so here on Earth, there must be a reason for that. It is likely that life chose multiple pathways initially, but only the most successful won out.
Within a given chemosystem, the laws of physics and chemistry would likely drive life toward the most efficient pathways and structures, meaning that even if multiple options exist initially, natural selection would favor the best-adapted solutions. This has major implications for understanding the universality of biochemistry and for astrobiology—it suggests that alien life, while perhaps different in some details, would likely follow similar biochemical constraints.
1. Deterministic Chemistry and the Inevitability of Certain Pathways
If physics and chemistry are deterministic, then under the right conditions, life is inevitable because:
- Certain molecules are more stable and more likely to form.
- Some reactions are more efficientand thus selected for.
- The availability of elements in the environment constrains what pathways are possible.
For example, Earth’s life could have used arsenic instead of phosphorus in DNA (as some extremophiles were once hypothesised to do), but phosphorus is vastly more chemically stable and efficient for energy transfer (ATP) and nucleic acid formation. The same applies to:
- Carbon vs. Silicon: Silicon is chemically possible, but it forms rigid, brittle compounds rather than the flexible chains and rings that carbon can form in water-based environments.
- Water vs. Ammonia: Ammonia can dissolve organic molecules, but it is less effective than water due to weaker hydrogen bonding and a lower liquid temperature range.
2. Convergent Biochemistry: The Survival of the Fittest Chemical Pathways
While early life may have experimented with multiple chemical pathways, only the most successful would persist, leading to a kind of convergent evolution at the biochemical level. Some examples:
- Proteins vs. Alternative Catalysts: While life could theoretically use mineral surfaces or ribozymes (RNA catalysts) instead of proteins, proteins allow for much greater structural and functional diversity.
- DNA/RNA vs. Other Genetic Systems: Other self-replicating molecules might have been possible, but DNA and RNA offer stability, error correction, and efficient information storage.
- ATP as an Energy Carrier: There are other potential energy carriers, but ATP is extremely efficient at phosphate group transfer, allowing rapid and reliable energy use.
The fact that life on Earth overwhelmingly settled on one version of each of these key systems suggests that they were the best options avaiable in our chemical environment.
3. Would Life on Other Planets Use the Same Pathways?
If the same physical and chemical rules apply everywhere, then alien life in a similar environment, such as Earth like planets with water and hydrogen based chemistry, would likely converge on similar solutions.
- DNA/RNA or a near-identical alternative for genetic storage.
- Proteins for catalysis and structural functions.
- ATP or a similar phosphate based energy molecule.
- Lipid membranes to create compartmentalisation.
However, in different environments, life might take alternative paths that are still optimised for those conditions.
- In methane seas (like Titan), life might use non-polar solvents and silicon-based molecules instead of water and carbon.
- In high-pressure super-Earth oceans, extreme piezophiles (pressure loving organisms) might have different adaptations in their membranes and enzymes.
But even in these cases, the most efficient chemical pathways in that specific chemical environment would likely dominate, meaning that different forms of life might still show internal convergence within their respective ecosystems.
4. Implications for the Origin of Life and Evolution
- If multiple pathways were tested at the origin of life, it suggests early Earth may have had a diversity of biochemical outcomes, but most were outcompeted by the winning formula.
- If abiogenesis happened more than once on Earth (a theory called the Shadow Biosphere Hypothesis), then lifeforms with fundamamental different biochemistry should have existed at some point. However, we have found no evidence of such alternate life today, suggesting either they were never there, or that they were wiped out by the dominant life form.
- If we ever find alien life, the first question will be – Is it chemically similar to us? If so, that would confirm that certain biochemical signatures dominate biochemistry due to efficiency.
The deterministic nature of physics and chemistry likely means that within any given planetary system, chemistry, and thus life, will be forced to follow the most efficient pathways, just as we see in life here on Earth. Life may have and does experiment with alternative pathways initiially, but it is clear only the most dominant, and thus efficient, biochemical pathways persit, which ultimately may lead to biochemical convergence. This could suggest that while alien life may be different in some ways, it may be unlikely to be wildly different in the basic functions of life, thus, if life emerges from the chemosystem on a given world, it may look chemically similar to the life we find here on Earth.