Lecture 2: Cellular Basis of Life
Evolution of the cell/Common origin of cellular Life:
The same basic molecular mechanisms govern the lives of both prokaryotes and eukaryotes,
indicating that all present-day cells are descended from a single primordial ancestor. How did this
first cell develop? And how did the complexity and diversity exhibited by present-day cells
evolve?
Several theories have been put forward to try and explain the origin of the first form of cellular
life. Viz:
1. The special creation theory: this theory is supported by most of the world’s religions and
civilisations. This theory states that cellular life was created by a supernatural being at a
particular time.
Since the process of special creation occurred only once and therefore cannot be observed,
this is sufficient to put the concept of special creation outside the framework of scientific
investigation. Science concerns itself only with observable phenomena and as such will
never be able to prove or disprove special creation.
2. Spontaneous generation theory: This theory states that life arose from non-living matter
on numerous occasions by a process of spontaneous generation. Aristotle (384 – 322 BC),
often hailed as the founder of biology believed that life arose spontaneously. Aristotle’s
hypothesis of spontaneous generation assumed that certain particles of matter contained an
active principle which could produce a living organism when conditions were suitable.
This theory was refuted in 1688 by Francesco Redi, an Italian biologist, who by a series of
experiments, showed that life can only arise from pre-existing life, the concept of
biogenesis.
3. Steady state theory: This theory states that cellular life has no origin. This theory proposes
that species have always existed and that in the history of a species, the only alternatives
are for its numbers to vary or for it to become extinct.
4. Cosmozoan theory: This theory does not offer a mechanism to account for the origin of
cellular life but favours the idea that it could have had an extraterrestrial origin. It does not
therefore constitute a theory of origin as such but merely shifts the problem to elsewhere
in the universe. The theory states that life could have arisen once or several times in various
parts of the universe. It’s also called the theory of panspermia. Sightings of UFOs, cave
drawings, provide evidence for this theory.
5. Biochemical evolution theory: This is the most accepted theory by scientists. This theory
postulates that cellular life arose according to chemical and physical laws. The speculation
regarding the formation of the first living cell is as follows
It appears that life first emerged at least 3.8 billion years ago, approximately 750
million years after Earth was formed. How life originated and how the first cell
came into being are matters of speculation, since these events cannot be reproduced
1
Evolution of the cell/Common origin of cellular Life:
The same basic molecular mechanisms govern the lives of both prokaryotes and eukaryotes,
indicating that all present-day cells are descended from a single primordial ancestor. How did this
first cell develop? And how did the complexity and diversity exhibited by present-day cells
evolve?
Several theories have been put forward to try and explain the origin of the first form of cellular
life. Viz:
1. The special creation theory: this theory is supported by most of the world’s religions and
civilisations. This theory states that cellular life was created by a supernatural being at a
particular time.
Since the process of special creation occurred only once and therefore cannot be observed,
this is sufficient to put the concept of special creation outside the framework of scientific
investigation. Science concerns itself only with observable phenomena and as such will
never be able to prove or disprove special creation.
2. Spontaneous generation theory: This theory states that life arose from non-living matter
on numerous occasions by a process of spontaneous generation. Aristotle (384 – 322 BC),
often hailed as the founder of biology believed that life arose spontaneously. Aristotle’s
hypothesis of spontaneous generation assumed that certain particles of matter contained an
active principle which could produce a living organism when conditions were suitable.
This theory was refuted in 1688 by Francesco Redi, an Italian biologist, who by a series of
experiments, showed that life can only arise from pre-existing life, the concept of
biogenesis.
3. Steady state theory: This theory states that cellular life has no origin. This theory proposes
that species have always existed and that in the history of a species, the only alternatives
are for its numbers to vary or for it to become extinct.
4. Cosmozoan theory: This theory does not offer a mechanism to account for the origin of
cellular life but favours the idea that it could have had an extraterrestrial origin. It does not
therefore constitute a theory of origin as such but merely shifts the problem to elsewhere
in the universe. The theory states that life could have arisen once or several times in various
parts of the universe. It’s also called the theory of panspermia. Sightings of UFOs, cave
drawings, provide evidence for this theory.
5. Biochemical evolution theory: This is the most accepted theory by scientists. This theory
postulates that cellular life arose according to chemical and physical laws. The speculation
regarding the formation of the first living cell is as follows
It appears that life first emerged at least 3.8 billion years ago, approximately 750
million years after Earth was formed. How life originated and how the first cell
came into being are matters of speculation, since these events cannot be reproduced
1
