And in The Beginning...
In simple terms, it appears that the Earth formed some 4.5 billion years ago, as a large and very hot lump of rock and molten iron, which we might reasonably assume could not have initially supported life. Despite such a hostile initial environment, we know that life did emerged and so we are left to ponder two basic questions:
What is a living system?
How were living systems created?
We may wish to initially turn to a dictionary to see if there is already a suitable definition. In my dictionary, under the word `life` there are the following eight interpretations:
- A quality manifested in functions such as metabolism, growth, response to stimulation, reproduction by which living organisms are distinguished from dead organisms or inanimate matter
- Living organisms collectively, i.e. plant life
- A living being
- The interval between the birth or inception of an organism and its death
- A biography
- Human activities and relationships, i.e. everyday life
- A manner of living, i.e. country life
- Animation, liveliness
Of the eight definitions, only the first goes some way to describing the attributes that separate the living from the non-living. However, even here there are problems in the details, for example, crystals can grow, computer viruses can reproduce. Clearly, we have an intuitive perception of the difference between living and non-living matter; however, it appears surprisingly difficult to be precise about what the key differences really are. The following list has been suggested as a possible encapsulation of some of the essential features of a living system:
- Self-organised, non-equilibrium system
- Governed by an internal program
- Which can reproduce itself
While possibly providing a starting point for discussion, I am not sure that life can be even remotely analysed in these simple terms. Any examination of the facts about life, as we know it, immediately tells you one thing, life seems to be a very complicated process. Although, the following phased process will undoubtedly be yet another simplifications to those already deeply involved in this subject, it is hopefully still reflective of the issues that have to be taken into consideration:
- Phase-1: Physical chemistry
- Phase-2: Chemical structure and function
- Phase-3: The aggregation of functions
- Phase-4: The aggregation of cells
- Phase-5: The emergence of intelligence & sentience
Phase-1 highlights the dependency of living systems on non-living systems, i.e.
i) Fundamental physics
ii) Molecular chemistry
iii) Active thermodynamic structure
First, we need to understand the establishment of the Earth's earliest ecosystem. This system is inorganic in nature based on the physics of Earth's position within the solar system and the molecular resources at its disposal. However, the Earth has been an active thermodynamic system from the start as it absorbs high-frequency energy from the Sun and radiates low-frequency energy into space. The Earth was never just a lump of rock floating in the empty vacuum of space, in a sense; it was a live birth. We also need to understand the process by which a single cell might have evolved from the non-living chemistry being generated by the Earth's active thermodynamic systems. We know that this process must have taken hundreds of millions of years. However, during this time, in which billions of molecules were created and destroyed, some molecules seem to have started to develop certain functional characteristics that persisted.
Phase-2: Chemical structure and function
Life is complex and possibly alludes to a structure evolved from simpler functions:
i) Functions start to persist by replication
ii) Functions start to adapt to the surroundings
iii) Functions start to react to stimulus
iv) Functions start to become capable of `cause & effect` responses
v) Functions start to retain `memory & recall` of responses
vi) Functions start to become self-organising and self-perpetuating
At first, the definition of life has to be closer to molecular chemistry, but a process that appears to be thermodynamically active from the outset. The chemistry of these systems starts to develop different functions that are capable of reacting to the environment and capable of replicating in the sense that the number of these systems grows. As we introduce increasing levels of differentiation, we come to a point that functions start reacting to stimulus, albeit in a simple `cause & effect` manner. Equally, these responses are being incorporated into the self-perpetuating functional make-up of the structure. Note, this is still molecular chemistry, as we have not as yet even reach the evolutionary level of a single organic cell.
Phase-3: The aggregation of functions
The complexity of life requires functions to be co-ordinated and adaptable:
i) Different functions start to aggregate within symbiotic relationships
ii) Collective functions start to evolve via a form of natural selection
iii) Collective functions develop collective purpose
iv) Collective purpose is greater than the sum of the parts
At some point, molecular chemistry becomes organic chemistry. Individual structural functions combine to create a collective function of the earliest, most primitive cells. Somehow the spark of life has been ignited and life is on its way. However, the process from these earliest single-cell organisms to the first multi-cell organism will take another 2-3 billion years:
Phase-4: The aggregation of cells
The aggregation of function culminates in a viable self-replication structure called a cell. The criteria of what we identify as a living system have been met and appears to only require one additional ingredient - time.
i) Aggregation is accumulative; cells now aggregate in symbiotic relationships
ii) Clusters of cells take on higher specialised functions.
iii) Replication evolves into reproduction
iv) Higher life forms continue to evolve by natural selection
v) The taxonomy of life explodes to fill the growing ecosystem
So, once started, the evolution of life continues to expand and diversify. This process will continue in this fashion for the next billion years or so, with life being driven by the interdepencies of `survive and reproduce`. However, somewhere along the 1 billion years of evolution between Phase-4 and the present-day, a new facet of life starts to emerge.
Phase-5: The Emergence of Sentience
While the process of natural selection is generally understood there are possibly some common misunderstandings. While supporters of `intelligent design` may disagree, there appears to be no evidence that there was an implicit driving force within evolution destined to give rise to increased intelligence and sentience. If so, its appearance may be explained purely in terms of survival benefits, but then again, maybe not.
i) Cluster of cells evolve as a brain function
ii) Life has a degree of intelligence to help it survive
iii) Spatial awareness is relative to self
iv) Self awareness allows anticipations of others
v) Collective groups can increase survival
v) Self awareness leads to sentience
Of course, there is also the theological argument that the nature of intelligence and sentience transcends the description of a physical system. However, we will conclude our speculative process at this point with the statement that scientific observation suggests that intelligent life did appear to evolve from an inorganic thermodynamic system, although it cannot yet explain how the 'genesis' of a cell took place.
Note: Some wider aspects of
evolution are discussed in the link
provided, which covers the first few billion years of relatively
speculative assumptions plus the broad classification of different
evolutionary eras and periods covering the last 2 billion years or
so, where the 'tree of life' appears to have flourished and been
recorded in the fossil record.