My personal research theme is the exploration of the origin of life.
All organisms on Earth, be it humans, animals, or plants, are composed of cells. Originally, unicellular organisms, which lived solely as a single cell, evolved and diversified through genetic mechanisms, leading to the current ecosystem.
So, how were these unicellular organisms created? Exploring this mystery is the pursuit of the origins of life.
In this article, I will begin by explaining my personal research stance and provide an overview of the chemical evolution theory I base my work on.
I will then delve into two crucial aspects necessary for the establishment of cells through chemical evolution: a self-reinforcing feedback loop and the assurance of dynamic diversity.
I believe these two points are essential because, even before the birth of DNA-carrying cells, mechanisms for reproduction and variation without DNA are necessary. A self-reinforcing feedback loop enables reproduction without DNA. Furthermore, mechanisms to ensure dynamic diversity are needed to form various substances without relying on DNA mutations or combinations.
Later, I will discuss the hypothesis that the formation of the self-reinforcing feedback loop and the mechanism to ensure dynamic diversity leverage the Earth’s water cycle.
Previously, I had posited that the Earth’s water cycle played a significant role in the origins of life, focusing only on the flow of water in its liquid state. However, I recognized challenges in the formation of the feedback loop solely from this perspective.
In this article, I introduce a new hypothesis emphasizing the importance of the water cycle in its gaseous state, where water evaporates from the sea to form clouds that bring rain to the land. This perspective clarifies challenges in feedback loop formation and also highlights the significant effects of the gaseous water cycle in ensuring dynamic diversity.
Having given this extensive introduction, I will now explain in detail.
My Personal Research Perspective
Generally, the exploration of the origins of life focuses on how components like DNA and cell membranes are chemically formed. As I’m not an expert in chemistry or biology, I cannot engage in such detailed research.
However, I view cells as systems. The mechanism leading to the birth of cells is also a system. Therefore, from a systems engineering perspective, I believe it’s possible to analyze how cells operate as systems and under which conditions a system can produce cells.
Of course, I cannot analyze at the level of specific chemical compositions or cellular components, so my personal research focuses on abstract structures and mechanisms.
Chemical Evolution
There are generally two camps: one that believes life came from outer space and the other that believes life originated from non-living chemical substances on Earth. The theory of chemical evolution belongs to the latter.
When there was no life on Earth, only chemical substances existed. It was possible for inorganic chemicals to evolve into organic substances through energies like lightning, surfaces of minerals, and hydrothermal vents.
Organic compounds are the building blocks of life. However, the organic compounds produced in the aforementioned ways are very simple. Constructing a cell, the smallest unit of life, requires vastly more complex groups of organic compounds.
Thus, to progress from simple organic compounds to complex cells, the theory posits that these compounds evolved over time, a process known as chemical evolution.
Primary Locations of Chemical Evolution
Chemical evolution progresses through accumulations of processes where inorganic and organic substances combine or interact under energy influences.
Chemical evolution is believed to have primarily occurred in water bodies like ponds or lakes. By accumulating materials for chemical evolution in ponds or lakes, more frequent chemical reactions can be anticipated.
Moreover, compared to land or air, there are more opportunities for chemicals to mix. Some inorganic and organic compounds can ionize, or exhibit acidic or alkaline properties, enabling diverse chemical reactions.
Given that water is indispensable for biological activity, it is logical to believe that chemical evolution primarily took place in water.
Key Point 1 of Chemical Evolution: Self-Amplifying Feedback Loops
For steady progress in chemical evolution, it’s essential to form a feedback loop that accompanies self-amplification. Even if a few new organic molecules form by chance, if they are not reproduced, these molecules will eventually break down and won’t contribute to evolution.
For instance, if a new organic molecule A is produced, and this promotes the synthesis of other organic molecules, then the chances of molecule A being synthesized again increases. Such feedback can be said to have a self-amplifying nature.
If a self-amplifying feedback loop is established, newly formed organic molecules can be expected to be produced continuously.
Considering the complexity of the components and cells themselves, numerous such feedback loops need to form.
Starting from the formation of feedback loops for basic, simple organic molecules, and using that as a foundation, feedback loops for slightly more complex organic molecules form, and this process repeats.
Key Point 2 of Chemical Evolution: Ensuring Dynamic Diversity
Believing in chemical evolution implies that complex aggregates of organic molecules capable of forming cells automatically arise from simple organic molecules. In this process, it’s essential to try out many combinations of organic molecules.
Moreover, it’s not enough just to find the right combinations; these combinations must also form the aforementioned feedback loops. If an organic molecule forms but doesn’t create a feedback loop due to the surrounding environment, it might be produced once and then vanish.
In waters containing the same substances at the same concentration, chemical evolution might saturate and stop. To break this saturation, new types of substances need to be introduced regularly.
Considering this, environments testing diverse combinations of organic molecules are essential for chemical evolution. Evolution needs not only a stable environment but also environments that change over time. Thus, a mechanism ensuring constant dynamic diversity is considered necessary.
Mechanism 1 Supporting Chemical Evolution: Liquid Water Circulation
In a single water source, chemical evolution might saturate and halt. By occasionally exchanging organic molecules between different water environments, the saturation state of chemical evolution can be disrupted, allowing continuous evolution.
A typical example of such exchanges is river flow. Organic materials move between water sources, flowing from upstream ponds to downstream ones, and eventually into the ocean. This ensures dynamic diversity and the synthesis of new combinations of organic molecules.
However, self-amplifying feedback loops don’t form in this process. Rivers just flow downstream. Organic molecules formed downstream don’t influence upstream ponds.
While there are rare phenomena like backflows in rivers or tidal fluctuations that make water flow loop-like, they occur in very limited locations.
If exchanges of organic molecules only occur through the flow of liquid water, even if newly formed organic molecules are beneficial, reinforcing their production is challenging. This makes ascending the evolutionary ladder difficult.
Mechanism 2 Supporting Chemical Evolution: Gaseous Water Circulation
Thus, focusing not only on the flow of liquid water but also on gaseous water, namely water vapor and cloud movement, can resolve this issue.
Light organic molecules produced in downstream waters can drift into the air, ride on water vapor to become clouds, be carried by winds, and fall as rain into upstream ponds, forming a feedback loop.
In today’s clouds, countless bacteria are present. Before the advent of life, when bacteria weren’t present, clouds probably contained numerous organic molecules.
When seawater evaporates, dissolved inorganic and organic materials can’t remain in the vapor. However, many of these materials, including bacteria, can drift in the air. The components of bacteria, which are smaller organic molecules, can certainly move through the air.
Riding on the upward currents of water vapor and winds, entering clouds, and then falling on land with rain is imaginable.
Inside the Clouds
There’s a famous experiment, the Miller experiment, that confirmed organic molecules can be produced from inorganic materials. By repeatedly applying electric currents in an apparatus containing inorganic precursors to amino acids, amino acids were produced.
This experiment indicates the potential for organic molecules to be synthesized inside clouds by lightning. Furthermore, if we consider that more complex organic molecules were synthesized and feedback from the sea to the land via clouds, not only in ponds or lakes but also in clouds, chemical evolution might have been progressing.
Patterns of Organic Matter Movement
When organic materials mix in ponds or water, there are three patterns.
The first pattern is when water containing organic matter mixes entirely.
For instance, if ponds nearby connect due to increased water from rain, the organic materials in each pond will mix. I call this pattern “Conjunction.”
The second is a pattern where only specific parts of the organic matter move to another body of water.
This is represented by the flow of a river. Typically, in ponds or lakes, lighter organic matter accumulates at the top, while heavier ones either float in the water or settle at the bottom. From such a pond, organic matter moving out following a river would primarily consist of lighter ones. I refer to this selective movement pattern as “Communication.”
The third pattern is selective yet broadly diffuses in multiple directions.
For example, volatile organic compounds can spread around on the wind or even move long distances on clouds. Although there are limitations based on wind direction and distance, it allows for a broader range of movement than river flow. I propose to call this pattern “Broadcast.”
Network Effects in Chemical Evolution
Due to the movement of organic matter in forms like Conjunction, Communication, and Broadcast, even if chemical evolution becomes saturated at various watering places on Earth, new organic matter can intrude, prompting further chemical evolution.
Especially with just Conjunction or Communication, the range of ponds or puddles for exchange becomes limited. However, when considering movement by Broadcast, the range of organic matter movement and new combinations potentially skyrocket.
There’s a concept known as the “network effect.” It’s a general principle where, like in social media, as the number of players in a network increases, the effect of their interactions expands not merely additively but multiplicatively or exponentially.
For instance, with just three people — A, B, and C — you only have AB, AC, and BC as combinations. Add D, and you get AD, BD, and CD, totaling six patterns. Add E and it becomes ten patterns, and with F, fifteen patterns. As more players join, the number of relationships between them grows exponentially, resulting in a network effect.
The Broadcast in chemical evolution indeed triggers this network effect.
It’s undeniable that organic matter has continuously moved through the countless ponds, lakes, and oceans on Earth, including by Broadcast. The combinations of these would have been virtually innumerable.
This increased the opportunities for new combinations of organic matter, likely making it easier to find enhanced feedback loops.
The Big Picture of Chemical Evolution: The Earth-wide Process of Cell Formation
I believe that chemical evolution progressed in this manner, utilizing the Earth’s entire topography and the circulation of both liquid and gaseous water. This achieves the dynamic diversity I emphasized.
Within this context, the self-enhancing feedback loop I highlighted was likely formed. Especially considering the possible use of gaseous circulation in addition to the liquid one for the movement of organic matter, this carries significant meaning for the formation of this feedback loop.
Thus, step by step, in the ever-diverse environment of Earth with its self-reinforcing feedback loops gradually forming, chemical evolution proceeded. This paints a picture where life’s birth was a process that slowly unfolded, making use of the entirety of our mother planet, Earth.
I believe that through the vast accumulation of this process, complex organic substances formed.
During this process, sugars that stored energy likely appeared, as did lipids that also stored energy and possibly provided a membrane that could encapsulate the organic soup.
Furthermore, proteins formed from amino acids, RNA from nucleic acids, and they likely developed some form of self-preservation or self-repair function. As these capabilities evolved, the precursor to self-replicating DNA would have emerged.
Through chemical evolution, organic matter evolved intricately. Materials for cells assembled, and eventually, with everything required packaged inside a membrane, a cell was born.
In Conclusion
In this article, I have not discussed the order in which these specific intracellular structures originated. Such studies are indeed the research topics that specialists have been working on for a long time.
Instead, I have outlined my hypothesis on how diversity and feedback, essential for chemical evolution, can be ensured through specific mechanisms.
What I find appealing about this hypothesis is the idea that, when considering that chemical evolution progressed while gradually forming feedback loops and solidifying its foundation, by the time the first cell appeared, the surrounding environment was conducive to its survival.
If we think of scenarios where cells suddenly arrived from space or materials instantaneously assembled into complex structures resulting in the emergence of cells, even if their initial appearance was miraculous, explaining how these cells managed to survive thereafter becomes challenging.
Of course, we cannot observe the ancient Earth environment with our own eyes, so any hypothesis we propose remains speculative.
However, by combining the current knowledge and insights, it is possible to describe a more probable mechanism. I am pursuing my research with this aim, focusing on the external mechanisms in the origins of life.
Reference:
The results of my past personal research on the origin of my life are summarized in the following preprint paper. It outlines the ecosystem structure I envisioned, and the interdisciplinary strategy to unravel the mystery of the origin of life.
