How life started on Earth is a great mystery. One of the biggest questions is
what kick-started the process. Some speculate that life sprung out of a primordial soup
of churning organic chemicals. There appears to be a very pivotal line between
complex chemistry and the evolution of life itself. The problem is that we understand so
little about this time or the process itself that it is difficult to know exactly what happened.
Now a team of researchers have been able to conduct experiments that seem to show that
RNA is capable of self-replicating and evolving while working as a collective.
Let's dive in and find out more.
DNA is essential to almost all life on Earth,
yet biologists think that life actually began with RNA.
DNA consists of two strands, arranged in a double helix whereas RNA only has one strand but both
are made up of similar nucleotides which store the genetic information. DNA is much longer than RNA.
RNA has some tricks up its sleeve that DNA does not have. It can fold into complex
shapes that can clamp onto other molecules which can then speed up chemical reactions.
DNA on the other hand is a more stable molecule.
UV light can easily damage a DNA strand whereas RNA is more resistant to damage from UV.
An experiment conducted by scientists from the University of Tokyo is revealing the remarkable
talents RNA seems to possess and suggests that RNA may well have been the original mechanism
for the storing and alteration of genetic material in early life.
More remarkable was that their RNA system was capable of evolving all by itself.
They discovered that the single RNA species evolved into a complex replication system.
It created a sort of replicator network which
comprised five types of RNAs with diverse interactions.
Normally the process of replication requires a cast of highly specialised organic materials,
like DNA and proteins to assist in this process.
RNA does not require these. This means that it could potentially make structures
that can physically build new molecules that can in turn build new structures. More than likely
this process is not perfect meaning that some of the replicator structures will do the job faster
or more efficiently than others and thereby will become the dominant form of RNA.
This is not a new concept, for decades they have known about self-constructing individual
RNA molecules but the problem was always that these were too simple and unstable to
be seriously considered as the forerunners to a DNA based system. But equally the problem with
DNA is that it lacks the ability to hold itself together long enough for the process to start.
The problem before was that their RNA analysis was based on individual RNA molecules. What if there
were multiple stands that were acting as a team? This is exactly what the scientist in this new
experiment were able to show. They demonstrated that they are capable of creating individual
replicator molecules that can operate collectively to not only preserve information and change over
time but to do so in such a way that the solution becomes more complex over successive generations.
Their experiment used cloned lengths of RNA in water droplets suspended in oil. These underwent
more than a hundred rounds of replication, with each round being tested and analysed.
Initially, the scientists doubted that such diverse RNA could evolve and coexist.
This to some extent goes against a core assumption in evolutionary biology.
The competitive exclusion principle, which states that more than one species cannot coexist
if they are competing for the same resource. This means that the molecules must establish a
way to use different resources one after another for sustained diversification. RNA is obviously
non-living but the scientists wondered if chemical species do spontaneously develop such innovations.
They were able to demonstrate that this is possible as long as the RNA don't compete with
one another for resources, but rely on one another in a sort of host-parasite manner. They discovered
that the removal of just one type of RNA replicator meant that they would all go extinct.
Recently we looked at the remarkable world of bacteria and saw that they seemed to work
better collectively than alone and in all likely hood this is how they first
appeared rather than as a single cell that eventually learned to cooperate with others.
We have also looked at the remarkable slime mould that is capable of storing memories
in the tube network and used these stored memories to make decisions for the collective.
The view that life tends to originate in isolation and later learns to develop cooperative behaviour
is something that needs to be reconsidered. If at a molecular level there can already be a tendency
for cooperation to benefit the formation of more complex RNA then this surely must equally extend
to all lifeforms. In fact, it also makes you question what exactly we should call living?
Here a lifeless molecule is seen to cooperate with other molecules
to form ever more complex versions of itself! And these molecules could eventually end up being the
mechanism by which life is able to not only store the blueprint to creating the life form
but also allow for adaptation to suit changing environments.