How did the first self replicating organism come into existence?

Question

When people try to explain evolution, they tell me that evolution is a cumulative result of mutations & natural section of the more superior individuals of a particular species. I think I'm fairly convinced with this explanation.

But when I think about it, all of them assume that there was an organism, however simple, that was capable of self replication & occasionally mutate. How did such an organism come into existence? Can anyone explain this?

An answer I found on Reddit didn’t really convince me.

Answer 1

Evolution or (as Darwin called it) "descent with modification" is a theory which explains the origin of the species NOT the origin of life. How the first life arose is completely irrelevant to the theory of evolution. What evolution does explain is how and why we have such variety of life on earth all descending from the same organism.

What you're asking about is not a theory of "evolution" but rather a theory of "abiogenesis." Although there are many interesting hypothesis for how abiogenesis happened (e.g. the RNA world, the "metabolism first" theory, etc.), the fact is we simply do not know yet how life first arose. What we do know is that life first arose between 3.5 and 3.9 billion years ago. That's a really long time ago compared to lots of other important events in natural history (even the Cambrian explosion where modern animal phyla evolved was only half a billion years ago), and so it shouldn't be surprising that it's a hard problem.

Answer 2

We don't know how self-replicating molecules first arose (and probably never will know exactly) but the Earth is large and had 500 million years (i.e. the prebiotic Earth timescale) or so to experiment in organic chemistry. The land-sea interface (such as tidal pools) are a good candidate site since these are areas where high concentrations of organic goodies can be found.

In this context, one focus that researchers have been looking at is self-replicating molecules.

For example, one lab in Cambridge,UK has come up with tC19Z.

tC19Z is the name of a RNA enzyme that acts like a self-replicating molecule. It can copy chunks of RNA almost 50% as long as itself. It can also make copies of other RNA enzymes. This molecule is not "alive" itself, but clearly demonstrates how greater complexity can arise.

Answer 3

They teach us in Physics that the entropy of an isolated system is always increasing or at least constant. Then how can an organism be born under these conditions?

The sun sends energy to the Earth, allowing for a decrease in entropy on Earth at the expense of the sun's entropy.

But when I think about it, all of them assume that there was an organism, however simple, that was capable of self replication & occasionally mutate. How did such an organism come into existence? Can anyone explain this?

That organism you're talking about is just a molecule that copies itself. Exactly how it has come about is not clear to me but it's not hard to imagine the possibility. A vast planet with molecules flying all over being bathed in ultraviolet light and if any molecule anywhere acquires the characteristic of copying itself, it will start growing exponentially and quickly spread all over the world.

Answer 4

This is an extremely interesting and extremely fundamental question, indeed, and thus far, biologists have failed at coming up with a satisfying answer.

We know that all the parts are there, we just don't know how they were arranged, or which ones go where.

The question is, in essence, composed of three sub-questions:

1. How did the fundamental building blocks of life come about?
2. How did the first self-replicating molecules come about?
3. How did cell membranes come about?

The answer generally takes the form of "On primordial Earth, a small selection of the billions of organic compounds generated when UV-light hits a mess of carbon dioxide, nitrogen and water where captured in a tide pool where concentration and foam led to random chance producing self-replicating molecules in proto-cells."

This answer, while almost certainly true, is also incredibly dissatisfying, because all it tells us is what deductive logic has already taught us, almost intuitively.

Incidentally, the fact that all of this happens with a million to one odds isn't a problem: The Earth is big, and the time frame for this happening is along the lines of hundreds of millions of years: Anything that might happen once per year by a million to one shot would likely happen hundreds of times in that timeframe.

In any case, when it comes to evolution, or Darwin's Theory of Evolution, or any other theory of evolution, this is all irrelevant.

Evolution is something that happens in any sufficiently complex (open) system, assuming it has the capacity to change at all.

It is most easily observed in living organisms, because they are at the right scale, and incredibly diverse, but it happens on all scales of the universe.

In fact, the easiest way to explain how life first originated, is just to keep counting backwards when you reach the Last Common Ancestor (of All Life on Earth), and propose models for how this proto-bacterium could be even simpler, until you're left with CO₂, N₂ and H₂O, and other simple molecules.

At that end of the spectrum it is well-understood that e.g. H₂O "evolves" from H₂ and O₂, because H₂O has a quality that makes it more "fit" than either of its components, chemical stability.

Furthermore, H2 "evolves" from free hydrogen by a similar mechanism, and free hydrogen "evolves" from protons and electrons, because it has the property of being electrically neutral, which is also a desirable property.

Of course, at the level of protons and electrons, things get a little muddy, and evolution kind of breaks down as a method for explaining how things come about.

Edit: For reference: Current Models of Abiogenesis on Wikipedia.

Answer 5

While many point to RNA, or a variant of it, as being the first molecule of "life" very few people know where it came from. Some suggest that it came from outer space because it's uncertain how the material for sugar-phosphate backbones could have developed on earth and that the perhaps these materials found their way here via meteorites. There are several hypotheses as to how an early earth environment may have promoted the properties of these molecules, but it's difficult to ascertain what exactly happened.

Somewhere within that abiogenesis wikipedia article is the mention of the role of deep-sea vents. The deep-sea vents and the currents that surround them basically facilitated a PCR reaction. Some of the early emerging DNA, maybe with some RNA and free nucleotides floating around, could have leveraged such an environment for replication and by sheer number (and some chance) entered into symbiotic relationship with other molecules to form the first cellular structures.

Answer 6

If you are interested in this question, I highly recommend you look at the work of Jack Szostak - Nobel Prize winner at Harvard who is currently doing some of the best work in this area. His work is grounded in good experiments that point to how abiogenesis could have happened.

Answer 7

I think that it started like this:

First stage:

Chemicals like Na, Cl, O₂, O₃, CO₂, CO, HCN, and H₂SO₄ react to form small molecules.

Second Stage:

Next those small molecules react to form macromolecules.

Third Stage:

DNA, being the most stable was first to replicate. A membrane eventually enveloped this and formed the nucleus

Fourth Stage:

Via Endosymbiosis it envelops mitochondria in an outer membrane

Fifth Stage:

Cell starts forming membrane and protein for all of its organelles. It is now a eukaryotic cell.

This is the DNA world Hypothesis.

Because DNA can be single, double, triple, or quadruple stranded in organisms(That would be ssDNA, dsDNA, tsDNA, and qsDNA respectively) it can do much more than just code for proteins or rRNA or tRNA.

In the single stranded state it can act like an enzyme forming deoxyribozymes.

In the triple and quadruple stranded states it can act inhibitory without needing another protein or methyl group.