How Did Evolution Begin?

Sep 28, 2009 By Lisa Zyga feature
The tree of prelife has two roots, 0 and 1, and infinitely many lineages. The perfect prelife catalyst is a string that enhances the rates of all chemical reactions in its own lineage (as shown in red for the string 0100). Partial catalysis occurs if a string catalyses some reactions in its own lineage (as shown in blue for the string 1000). Image copyright: Ohtsuki and Nowak.

(PhysOrg.com) -- Life's ability to replicate itself is essential for evolution, yet even the simplest kind of replication requires a relatively complex system. So what kind of non-replicating system might have served as the predecessor of evolution, paving the way for life as we know it? The answer, according to a recent study, is a kind of "prelife" -- a chemical system that can lead to information and diversity, and that is capable of selection and mutation, but does not yet have the ability to self-replicate.

In their study, Hisashi Ohtsuki of the Japan Science and Technology Agency and the Tokyo Institute of Technology, along with Martin Nowak of Harvard University, have investigated how might have first begun. As the researchers explain, the origin of is a transition from chemistry to biology, and has been widely studied. Here, Ohtsuki and Nowak have presented a model where a purely chemical system (prelife) becomes more efficient (catalytic prelife) and then builds the sequences needed for replication, finally resulting in life. Their work is published in a recent issue of Proceedings of the Royal Society B.

“As you know, the ability of replication is critical for life,” Ohtsuki told PhysOrg.com. “We can conceive several forms of life, such as prelife catalysts and replicators, as in our paper. We are interested in which form of life is most efficient and thus is selected in prelife (a soup of chemicals). The significance of our study is that we have mathematically shown for the first time that replicators, which have the ability to remain attached with a growing sequence, have a great advantage over the other forms of life. Replication is usually taken for granted in the study of evolution. We think that our result gives a justification of why replicators are so dominant.”

In the scientists’ model, prelife is made of two types of monomers (0 and 1) that randomly link together to form a . By adding a 0 or a 1, longer chains are produced from shorter ones. The researchers created a simple tree of life based on this growth process, where either a 0 or a 1 is added to the end of the preceding chain to make a longer one. Though starting with just a single monomer, this tree of prelife has infinitely many lineages.

As the researchers explain, some of these prelife sequences are catalysts, and can enhance certain reactions in prelife. Specifically, they increase the rate at which monomers are added to sequences in the specific prelife reactions that created them. The faster the rate of reactions to create a certain prelife , the more of them there will be. As the researchers found, the sequences that are most highly selected among prelife catalysts are perfectly catalyzed prelife sequences (those that enhance the rates of all their upstream reactions).

“Prelife refers to chemical reactions in a soup of chemicals that consists of amino acids, phosphoric acids, nucleobases, and so on,” Ohtsuki explained. “Simply speaking, prelife supplies ‘materials’ for life. But prelife does not have an ability of replication, because it cannot catalyze any reactions. Catalytic prelife is a big step forward for life, because it can enhance certain reactions. A most promising candidate for life among prelife catalysts are those which can catalyze their own upstream reactions. We believe that catalytic ability is a big step, yet not enough for the emergence of life, as we have shown in our paper: we need another step, that is, replicators.”

Replicators - for example, a simple sequence of all 0 monomers - are among the sequences that prelife dynamics can create. The difference between a replicator and a perfect prelife catalyst, as the researchers explain, is that a prelife catalyst attaches to a sequence to increase the rate at which an activated is added, and then detaches itself. In contrast, a replicator remains attached to the growing sequence.

“The fundamental difference lies in that replicators can remain attached to a growing sequence so that it can ‘go along’ with it,” Ohtsuki explained. “By doing so, replicators need to attach to a template only once to complete the replication. On the other hand, prelife catalysts have to attach to and detach from the target sequence many times, because in each reaction the target extends in length by one. Therefore, a longer prelife catalyst must catalyze its upstream reactions a number of times, resulting in an inefficient replication.”

Overall, replicators have certain advantages over catalytic prelife that cause the replicators to be selected over prelife. As the researchers explain, ongoing competition between prelife and catalytic prelife creates certain selection thresholds that limit the lengths of the sequences. Most importantly, the researchers found that catalytic activity must increase exponentially with sequence length to keep its abundance high; otherwise a longer sequence becomes less abundant. In contrast, the threshold of replicator activity converges to a fixed value, suggesting that even long replicators can sustain its high abundance. For replicators, the critical replication rate is almost independent of the rate of the replicator. As prelife catalysts and replicators compete for the same resources (monomers), this ability to grow longer is what gives replicators their edge, ultimately leading to the origin of evolution.

More information: Hisashi Ohtsuki and Martin A. Nowak. “Prelife catalysts and replicators.” . doi:10.1098/rspb.20091136

Copyright 2009 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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User comments : 17

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Alexa
4 / 5 (2) Sep 28, 2009
..the origin of life is a transition from chemistry to biology..

The transition from physics into chemistry would make explanation even easier, for example some liposomes can behave like walking droplets, described recently:

http://focus.aps..../v15/st7

We can imagine, such droplets precipitated from waves of ancient lakes at places, where organic compounds were preconcentrated by wind and solar radiation and they were thrown at coast surface, covered by various surfactants. The droplets are attracted to them, so they started to climb around coast, collecting these materials in their cells. The most successful droplets become so large by such way, they fragmented into smaller ones under impact of next breaker wave, and whole process has repeated many times, until well developed and movable droplets remained. Recently living examples of walking droplets were found: a single-celled giant amoebas of very ancient origin.
thales
3.5 / 5 (2) Sep 28, 2009
This model sounds very similar to Conway's Game of Life (http://en.wikiped...f_Life). It would be interesting to know what is the shortest possible sequence length that can replicate.
SincerelyTwo
4 / 5 (2) Sep 28, 2009
It began with the Big Bang.

Every form of matter is victim to the condition of its environment and associated circumstances. Some of those compounds over time formed organic molecules, which themselves are victim to the environments surrounding it. It all just grows and mutates in time reacting to all of the things around it. Where life can exist, it may... given the right stuff is around. I'm sure there are places where life exists and it simply doesn't due to lack of requirements, as circumstances may be.

Ridiculous amounts of time to allow matter to condense and large bodies to form, for more complex environments to grow... etc etc etc.

How could it be any more obvious?
SincerelyTwo
4 / 5 (1) Sep 28, 2009
Correction from my previous post (edit timer went out on me!).
***
"I'm sure there are places where life could exist and it simply doesn't due to lack of requirements, as circumstances may be."
irjsiq
2 / 5 (2) Sep 29, 2009
I am very comfortable with both Evolution and Creative/ Intelligent Design . . . the article refers to 'pre life'. . . ie. "We have not identified the exact '?monomer? moment that 'pre' was removed, and 'life'
became ! ! !"

Roy Stewart,
Phoenix AZ
magpies
Sep 29, 2009
This comment has been removed by a moderator.
thales
2 / 5 (1) Sep 29, 2009
I am very comfortable with both Evolution and Creative/ Intelligent Design . . . the article refers to 'pre life'. . . ie. "We have not identified the exact '?monomer? moment that 'pre' was removed, and 'life'
became ! ! !"

Roy Stewart,
Phoenix AZ


But the problem with that is there's also no evidence of the intelligent aliens that purportedly designed Terran life.
E_L_Earnhardt
Sep 29, 2009
This comment has been removed by a moderator.
irjsiq
1 / 5 (4) Sep 29, 2009
Thales
Then who made the aliens ? ? ?

Evidence aplenty! I found God in a Grass Root!!!
The next time you swallow, take a few moments to consider your epiglottis.
One can appreciate the wonder of balance and fragility of existence if one simply sees the wonders and how they function as a whole; either as an organism or an ecosystem.
Humans attempt to define God, and then our limited abilities hamper our efforts . . . Allowing the phenomenon of wonder to operate freely, no relgion no denial, no pre-conclusions . . . just the wonder of it all, the balance, the eons . . . A delicate 'crysal' from the bowels of the Earth, in perfect condition!
How did it survive the fault movements all around?
I solved the problem for myself . . . I am content with both per first line of original post.
An I am thankful for the gifts of Wonder and Apprecaition which take it all in.
Roy
irjsiq
1 / 5 (2) Sep 29, 2009
Thales,
an addendum:
Without the gift of Wonder, one is stuck in the Parking Lot at Disneyland/World . . . One can see the higher elevation so some of the rides . . .
With the gift of Wonder, one can appreciate the technical/mechanical expertise of the birthing All the rides . . . one can experience All the rides simultaneously without the long lines waiting for each ride!
Roy
verkle
Sep 30, 2009
This comment has been removed by a moderator.
Wadsworth
3 / 5 (1) Sep 30, 2009
All the religious commentators here obviously hate any scientific progress and will condemn anything scientists come up with. Of course the experiment was " Intelligently Designed",--by human intelligence. So we are back to square one, as the creationists will have to renew the assertion that there is some "other" intellignce around,- (their god), which "created" human intelligence.
Such a Being would have to have evolved its own intelligence, before it could create anything. We know for a fact human intelligence has evolved; and if you want to keep pushing your God into science, then please acknowledge that he also evolved,-and so did all his infinite number of Super-God grandparents. Oh, and how about introducing him to us so that we know he actually exists, and is not just a primitive fable.
Wadsworth
4.5 / 5 (2) Sep 30, 2009
Verkle
"This kind of thinking goes directly against the law of information. Things do not naturally become more complex."

O really?--your statement is a typical example of the logical fallacy of Equivocation,--changing the meaning of words.
A grown animal not more complex than a single celled Amoeba?
A DNA molecule not more complex than the phosphates, riboses, purines and pyrimidines that make it up?
A star not more complex than an atom?
As (real) complexity increases, so does its information carrying capacity. DNA is a genetic code, a H2O molecule is not.

And why may I ask is this Phyorg site polluted with fanatical God-botherers? Please keep science and religion separate.

Wadsworth
3 / 5 (1) Sep 30, 2009
Wadsworth--my first comment above, was actually in reply to the comments under:

"Scientists develop first examples of RNA that replicates itself indefinitely
Jan 09, 2009 | not rated yet | 0 Now, a pair of Scripps Research Institute scientists has taken a significant step toward answering that question. The scientists have synthesized for the first time RNA enzymes that can replicate themselves without the help ...

--which is now closed to comments. They did annoy me though.
E_L_Earnhardt
1.5 / 5 (2) Sep 30, 2009
"Which came first - The chicken or the egg?" This old question has been much debated, but never answered conclusively. Physics is with the chicken.
Chemistry is with the egg. I say "design" comes before any construction!
Wadsworth
5 / 5 (1) Sep 30, 2009
EL Farnhardt

Their ancestors evolved together.
thales
5 / 5 (1) Oct 01, 2009
Thales
Then who made the aliens ? ? ?

Duh, the other aliens.

BTW: Earnhardt, thanks for giving me my new favorite phrase: "Physics is with the chicken."
AWT
Oct 03, 2009
This comment has been removed by a moderator.
Husky
3 / 5 (2) Oct 04, 2009
regarding the comment "Things do not get more complex naturally" Well, not by themselves, they will not get more complex, (read: entropic/energy state), UNLESS offcoarse, energy is added from an external source, in other words: things can get more complex at the expense of something else losing complexity. A prime example would be the black smokers/hydrothermal vents that, while losing energy/entropy, in doing so deposit soluble minerals on their own smokestacks, now the interesting thing is, that depending of the solubillity as determined by the temperature of the water and the height of the smokestack, different minerals will be deposited at different heights, effectively creating a basic distillery/refinery mechanism. For stackmaterial to remain attached it has to withstand the stacktemperature at that height, a basic selectionprocess for height/temp specific catalystic actions, so, more "fit" materials will make up/deposit the own stack (otherwise it wouldnt grow in the first place
Husky
4 / 5 (2) Oct 04, 2009
But wait , it gets better, as the smokestack grows (evolves) the reactionzones change in height/temperature, creating a need for reaction zones to get acustomed to their new height temperature, another selection proces for selectimg materials that can deposit within a broader range of temperatures, but this creates overlapping/competing reactionzones for the same materials etc.etc... leading eventually to simple/extremophile lifeforms in a way, where replicators have the advantage to go on as the stack grows while the catalyts tend to be stuck at niche places
Husky
4 / 5 (2) Oct 04, 2009
On a final note, it is not coincidental that one of the most primitive lifeforms, that is more complex than bacteria, is the giant tubeworm, that you will find near the black smokers and are in fact miniature versions of the smokestack temperaturegradient mechanism, a living proof of the fact that nature was on to to something when it build the vents...
BrianH
Oct 07, 2009
This comment has been removed by a moderator.