Theories of the Origin of Life.

Organic evolution

Organic evolution is a gradual change in the genetic composition of organisms in a population during successive generations leading to formation of new species from pre-existing species.

Forces/pressures leading to organic evolution

1. Primary forces

Are the ones which must be there for new species to be formed from pre-existing species. Thus, if absent no organic evolution takes place.

These forces include:

1. Mutation
2. Gene recombination
3. Natural selection

NB: Natural selection must be present with either one of the two forces (mutation and or gene recombination)

2. Secondary forces

These are forces that modify rate of organic evolution i.e. if present, rate of evolution of the species are faster, but if absent the rate is slower.

These include:

1. Gene flow
2. Genetic drift
3. Breeding
4. Adaptive radiation/geographic isolation

Theories of origin of life

a. Special creation

Species are immutable (not changing).

Life was created by a supernatural power at a particular time i.e. God made living things once upon a time and whatever is existing today is a result of reproduction. If God wants a new species he just says BE and there it is.

Strength of the theory:

• Faith: believing and accepting this with no evidence.

Weakness of the theory:

• Cannot be proved or disapproved by science as science goes with experiments and observation.

b. Spontaneous generation

This theory was common in ancient Chinese, Babylonian and Egyptians.

• Nature passes from lifeless to animals in an unbroken sequence.
• Particles of matter contained an active principle which could produce a living organism under favourable conditions. This active principle was present in fertilized eggs, seed, sunlight, wheat, decaying meat, natural forces and decaying earth, mud.
• Van Helmont (15^th century) did an experiment which gave rise to mice in 3 weeks; the raw materials were a dirty shirt, wheat grains and a dark cupboard. The active principle was thought to be human sweat.

Strength of the theory:

• Life arises from non-living matter on a number of separate occasions.

Weakness of the theory:

• In the experiments, there were no controls, in which each variable could systematically be eliminated.

c. Cosmozoan theory (Panspermia theory)

There has been an extra-terrestrial origin i.e. life arose on this planet from somewhere else. Life could have arisen once or several times at different times and on several parts of the universe.

Strength of the theory:

The sightings of UFOs, cave drawings of rocket like objects and 'spacemen' and reports of encounters with aliens provide the background for this.

Weakness of the theory:

• The theory does not talk about the origin of life but perpetuation of it.

d. Steady state

• Life has no origin.
• This theory asserts that the Earth had no origin, has always been able to support life, has changed remarkably little, if at all and that species had no origin.
• This theory proposes that species never originated, they have always existed and that in the history of species the only alternatives are for its numbers to vary, or for it to become extinct.

e. Biochemical evolution theory

The biochemical evolution theory, also known as the naturalistic theory, proposes that life on Earth originated from simple chemical compounds under specific physical and chemical conditions. According to this theory, life arose through a process of chemical evolution, where simple molecules like amino acids, sugars, and nucleotides were formed from basic elements like hydrogen, oxygen, nitrogen, and carbon. These simple molecules eventually combined to form more complex compounds, which were crucial for the development of the first living organisms.

Strengths of biochemical evolution theory:

1. Experimental testing — The theory is based on scientific principles and can be tested through experiments. For instance, laboratory experiments (like the Miller-Urey experiment) have successfully demonstrated the formation of amino acids and other organic molecules under conditions that simulate the early Earth.
2. Emphasis on amino acids and proteins — The theory correctly identifies amino acids and proteins as the fundamental molecules for life, acknowledging their critical role in the formation of living organisms.
3. Promotion of critical thinking — The theory encourages scientific inquiry and the development of inquisitive minds, as it challenges researchers to explore the origins of life using chemical and physical principles.

Weaknesses of biochemical evolution theory:

1. Transition from complex organic molecules to living organisms — While the theory explains how simple molecules could form complex organic compounds, it fails to adequately explain the transition from complex organic molecules to living organisms. Specifically, the origin of self-replication, metabolism, and cellular structures that define life remains unclear.
2. Incomplete understanding of the first cells — The process by which coacervates evolved into fully functioning, self-replicating cells is not well understood, and this remains a major gap in the theory.
3. Alternative theories — Some scientists propose alternative theories of life's origin, such as the RNA World Hypothesis, which suggests that life may have started with RNA molecules capable of self-replication, before the evolution of DNA and proteins.