I have heard a million times over that because science cannot explain life’s origin then evolution must be wrong. Those who preach this fail to understand one important fact; The logic of evolution is not at all pegged on how life may or may have not originated. Evolution primarily deals with how life changed after its conception. It deals with how the diversity of life present in fossil records and the extant ones originated from a common ancestor. Even the definition of evolution does not encompass the origin of life. Evolution, biologically, is defined as a change in the allelic frequency of a population. Alleles are the property of living organisms. Therefore debating on this definition only, common sense tells us that evolution deals with already pre-existing life forms.
Abiogenesis; the study of how life may have originated, studies how chemical reactions in the primitive earth some 3.5-3.8 million years ago may have created the first organic materials that gave rise to the ancestor of all life on this planet.
The realm of abiogenesis and the realm of evolution are not one and the same thing. What is true is that abiogenesis gave way for evolution. These two areas are connected by way of the first life form(s). A shift on either side of this boundary reveals that different forces and laws govern the two processes. Whereas abiogenesis is governed by the laws of thermodynamics (chemical reactions are thermodynamically governed) evolution is governed by natural selection as the MAIN force (other forces are in play but natural selection in the fundamental force).
As explained above abiogenesis is a purely a chemical process. Abiogenesis therefore studies affinities of the different atoms that constitute life to each other to form complex compounds. Some argue that this happened under the direct influence of metallic catalysts under different sources of energy. Under these catalytic conditions, the atoms came together and formed precursors of major biological molecules. It is these precursors that are the subject of study under abiogenesis.
The aggregation of the molecules that formed in the prebiotic history of life also fall under abiogenesis. This aggregation has been defined into ways. That is, the RNA-first hypothesis and the Protein-first hypothesis. Just for the record, the fact that there are two clashing propositions does not mean that there is something wrong with abiogenesis as a study of life’s origins. What this means is that one of the two is true and as evidence from either side of the coin accumulate, science (Biology) will eventually reach a consensus. Such disputes in Biology are not rare. Debates raged for years as to whether proteins were the hereditary materials, between the sperm and the egg which one was the baby contained, nature versus nurture et cetera. But now evidence has grown almost exponentially to support genes as the hereditary materials and not proteins, evidence support that both parents contribute genetically in the offspring’s and that both nature and nurture are important in the expression of a characteristic.
The RNA-first hypothesis puts it forward that RNA was the first self-replicating molecule that appeared in earth’s history. However some have argued that there still may have been other pre-life systems, but so far they are speculations and have not caught on in the mainstream scientific debates. If you ask me, it will be very difficult to prove something that left very faint traces of its existence. Albeit this does not mean that I am disapproving them, what I am saying is that based on current evidence, they lose the case.
I understand the mind twisting effect that this brings. DNA, RNA and proteins are interdependent molecules. Therefore how can it be that one predates the other? I mean, DNA unzips and proteins form RNA from the unzipped section of DNA, RNA on the other hand forms proteins, DNA depends on proteins for its stability. This is a question of which came first; the egg or the hen.
The RNA-first hypothesis maintains that it is RNA that was first to form. So what is special about RNA that makes some believe that RNA came first? Well, the answer is relatively simple, RNA can act as both a catalyst and as a genetic material; properties of proteins and DNA respectively. It would therefore mean that the first protocells would be able to catalyse major metabolic reactions and have the ability to divide and thus reproduce. However since proteins and DNA are better suited in their specific roles, it is therefore plausible that only later in the history of life did they take these roles from RNA.
From my stand, I hypothesize that the first property that RNA must have had was self-replication. This according to me is the key to emergence of life. An autonomous self-replicating molecule would be needed to give rise to self-replicating cells that are the ancestors to all life forms. An intelligent mind will ask, ‘is there evidence to suggest that RNA is self-replicating?’ Watson was the first to suggest that RNA was may have been the first self-replicating molecule. He unfortunately did not have proof to back this claim. He only relied on the suspicion that RNA could both store genetic information and catalyse biochemical reactions. However all changed in 1982 when the first RNA enzyme was discovered. Since then the number of RNA enzymes discovered have grown. This gave an unexpected boost to the hypothesis that the first life consisted of RNA that could catalyse the production of more RNA molecules. But this does not answer the question the evidence availability. In the current life forms, RNA is synthesised using DNA and Proteins. Therefore, if RNA was self-replicating there is no evidence in nature. If you are still with me you will know that this does not go against my argument because we are talking about abiogenesis.
Biochemists in this field understood that the absence of evidence does not mean the evidence of absence, at least in this case. In 2001 a 189 nucleotide long RNA enzyme referred to as R18 was synthesized. It could synthesise a maximum length of 20 nucleotide long RNA, a mere 10% of itself. I understand that most people will see this a small feat and insignificant. Encouragingly in 2011 Philipp Holliger of MRC Laboratory of Molecular Biology published a paper in SCIENCE where he reported to have synthesised a RNA enzyme, tC19Z that could copy sequences of up to 95 nucleotides long and almost half the parent size. It is a great exploit, according to me, to create a self-replicating molecule that can replicate 50% of itself.
The ability to reproduce oneself is a characteristic of all life. But how does these self-replicating RNA do it? Taking tC10Z as an example, it clamps on the end of an RNA then attaches to the correct nucleotide then moves one step and adds another one. Another self-replicating system involves two RNA enzymes each composed of two subunits that catalyse each other. The first enzyme binds the two subunits and in turn the newly formed molecule joins the other two subunits thus the process is cyclic. Although this is outside biology molecular information has been immortalised; RNA is not alive but its sequence of nucleotides is maintained. Additionally if it is observed carefully this is seen that this a rudimentary form of sex. It should be understood that as long as the supply of nucleotides is maintained then the number of RNA molecules generated will increase indefinitely.
All this is beautiful but a sceptic would argue that all this are carried out in laboratory environments that are carefully chosen to make this reactions work. Let me be the first to point out that it has been rather difficult to create nucleotides in prebiotic conditions. Thus all the nucleotides that were used in all these experiments were created in postbiotic conditions. But it is of great importance to understand that this does not necessarily disqualify this line of thought. It may not be possible to synthesis RNA in prebiotic life yet, but as scientists we are SURE that there is a natural process outside biology that creates nucleotides, sugars and phosphates. And this three are the building blocks of RNA. Nucleotides are abundant in space and have been discovered in Asteroids and metiorites.