Dr Irengbam Mohendra Singh
This column is a continuing story about human search for non-god origin of life on Earth.It’s a scientific problem.Many scientists have been seeking the origin of life on Earth for ages, but so far no concrete evidence has been found. There are a few theories. The search is hardly any story connected with temples, mosques and churches. It’s a cosmological story. Religions rely on spiritual teachings that are all anodynefor non-scientific mind. Because of lack of evidence scientists do not accept them.
It’s now generally agreed that all life today evolved by a common descent from a single primitive lifeform, UCA (see below). Until the end of the 19th century, almost everyone believed that gods created the Earth and life on it. Any counterargument was considered bogus and the person proposing the idea an ‘untouchable’ atheist.Today, we live in a world that would have been unrecognisable to our 19th-century ancestors whose life was entirely god-bound.
The religious and philosophical thinking that god-created life is no longer true. The truth can only be denied by an abandonment of reason.Since the last century, afew scientists took upon themselves to figure out how life could have come out on Earth without gods’ help. In the West, some people havetried to create the Genesis moment with experiments in their laboratory, to create brand-new lifeform from scratch. None was successful.
On the other hand, modern scientists have been able to create the “building blocks of life”- amino acids from organic chemicals.It began with Russian Oparin (1924) and English Haldane (1929),who independently formed the hypothesis that young Earth, following exposure to various form of energy including lightning and radiation, had a reducing atmosphere that was conducive to form basic compounds. These compounds gathered in a small warm ‘soup’ and continued to react with themselves. Over time, they produced more and more complex molecules, eventually evolving into the first lifeform.
American Prof Melvin Calvin, winner of the Nobel Prize in Chemistry, wrote a book: Chemical Evolution and the Origin of Life in 1969, outliningthe idea that before life began there must have been a process of chemical change. As it is knownthat organic molecules were made relatively easily out of inorganic pieces, it’s more likely then, life sprang out of chemicals.
Most scientists are now confident that science will trace the birth of life on Earth, especially after Urey-Miller’s classic lab-experiment in 1952, to create the building blocks of life.They could demonstrate that most amino acids that arechemical constituents of proteins, found in all living organisms, can be synthesised from inorganic compounds under conditions intended to replicate those of the young Earth. The primordial soup theory has now a firm following in scientific circles since its inception in 1924,but the exact nature of how non-living chemicals changed into living things remains unanswered, though it’s put to ‘abiogenesis’.
Abiogenesis, or informally the origin of life, is the natural process by which simple organic matter arises from non-living matter. The transition from non-living to living entities was not a single event, but a gradual process of increasing complexity that involved molecular self-replication, self-assembly, autocatalysis and cell membranes. It has two theories: (1) protein-world or metabolism theory and (2) RNA- world or genetic theory. The relationship between the two is really like chicken and egg relationship.
Historically, only in late 19th century,scientists began to think about the origin of life afterDarwin’s publication of ‘On the Origin of Species’ in 1859.Darwin hypothesised how the vast diversity of life could have arisen from a single common ancestor instead of each of the different species being created by God. He explained how all the species were descended from a primordial organism that lived millions of years ago, known as the “last universal common ancestor” (UCA). But his theory of evolution said nothing about how the first organism came into being.
It was only in the early 1950s, scientists had moved away from the long-standing assumption that life was a gift from gods. The iconic 1952 experiment of Stanley-Miller convinced everyone that life possibly formed spontaneously and naturally on early Earth. By this time, many biological molecules including sugars, fats, proteins, and nucleic acids such as deoxyribonucleic acid (DNA) were discovered. That DNA carries our genes shocked the 1950s biologists.
There are two main theories about the origin of life: (1) metabolism or protein-world hypothesisie spontaneous formation of simple molecules and (2) genetics hypothesis or RNA- world hypothesisie genetic molecules can replicate and multiply themselves.
Protein-world hypothesis posits that four amino acids, namely, glycine (G), alanine (A), aspartic acid (D) and valine (V), the main components of protein were able to pseudo-replicate (artificially inflating the number) before the emergence of genes.
The widely accepted “RNA-world theory” argues that RNA – the molecule that today plays roles in coding, regulating, and expressing genes – elevated itself from the primordial soup of amino acids and cosmic chemicals. It eventually gave rise first to short proteins called peptides and then to single-celled organisms. The theory however, does not explain how the amino acid building blocks were first assembled into the proteins that formed the machinery of all cells. A further big problem that remains unsolved is how cells concentrated all their chemical components inside, enclosed by their cell wall or membrane, and how the cell wall was formed.
Among a few new theories of how prebiotic cells (before the arrival of living cells) evolved, there is one authored by Jeff Errington, British microbiologists, Director of the Centre for Bacteriological Cell Biology, Newcastle University (Cell press. 2013): How did early primordial cells evolve? The study shows a possible replication mechanisms of primitive (prebiotic) cells that could have existed before the explosion of bacterial life on the planet, nearly four billion years ago. Errington says: “Four billion years ago, soon after the planet cooled enough for life to begin, primordial cells may have replicated and divided without protein machinery or cell walls, relying instead on just a flimsy lipid membrane. These primitive cells could have evolved without such crucial structures. While the vast majority of bacteria have cell walls, many bacteria can switch to a wall-free existence called the L-form state, which could mirror the structure of primordial cells.”
The study also reveals how bacteria in this L-form state divide and proliferate by a simple mechanism that does not require any protein-based machinery.”The cell wall is a layered structure surrounding cells that protects them and maintains their shape. It’s present in all known major bacterial lineages, and it was also probably present in the last common ancestor of bacteria. This structure is so important that it is targeted by antibiotics, and many bacteria responsible for infectious diseases can switch to the L-form state to resist antibiotics,” Says Errington.
Errington and his team identified two genetic changes required for L-form growth in bacteria. One of these mutations was necessary for the increased production of fatty acids in the cell membrane, which would be expected to increase the cell’s surface area relative to its volume. Indeed, the researchers found that by artificially increasing cell surface area, they could induce L-form-like shape changes and cell division. The findings suggest that a simple biophysical change—an imbalance between surface area and volume—underlies L-form cell division.
A controversial new theory by a biophysicist Jeremy England, known as ‘Next Darwin’ at Massachusetts Institute of Technology (MIT), US,made waves in 2013.His hypothesis cast the origin of life from inorganic elements was a physical necessity, an outcome of thermodynamics. This was not a freak accident, but followed the laws of physics. As an expansion of Darwin’s theory of primordial soup, he said matter in the warm soup will become energy-efficient when driven by external energy sources as catalysts, like the sun’s photons. It will shuffle and organise themselves into organisms that would eventually lead to the birth of life on Earth.
The latest model of the possible origin of life comes from a press release from the Scripps Research Institute, California. A team of chemists, members of the Centre for Chemical Evolution (CCE), supported by the National Science Foundation (NSF) and the NASA Astrobiology Program, have revealed that key chemical reactions for life may have been possible with ingredients that were likely available on the Earth four billion years ago.
The study focused on a series of chemical reactions known as the citric acid cycle (TCA), which are essential for releasing energy in all living cells. TCA is also known as Kerb’s Cycle, by which living cells produce energy as ATP (cf. author’s article: Scientific discovery of human soul. TSE. August 19 2018). However, there is still a problem. Some chemicals used in the citric acid cycle were likely not present on the early Earth.
So, the new study examines an analogue cycle that could have feasibly functioned with ingredients that were available four billion years ago. The findings could be the first step in understanding how the citric acid cycle developed on Earth, but not the first life.
As in many cases of scientific discoveries, only time and further supportive evidence will tell if there is any truth in their claims. This is hard science.
The writer is based in the UK
Dr Irengbam Mohendra Singh