|Essay 12 02/14/2004: Biology, Organic Chemistry, Psychology
It is easy to see that all living organisms on our planet today are replicators. Each plant,
animal, fungus, protist and moneran is here now because its ancestors were able to
escape death, and successfully pass their genetic material on to their offspring. Since
the beginning of life on earth every member of each of the five kingdoms has been fine
tuned to accomplish one ultimate objective- replication.
Chemically, the genetic material used by all organisms on the earth is so uncannily
similar that most scientists believe that we all came from a single ancestor. It is
interesting to note that humans and bacteria share the same chemical systems for
replication, in fact they even share many of the same genes. The very first replicators on
our planet were most probably microscopic, organic molecules- strands of chemicals
that attained the ability to copy themselves sequence by sequence. It is thought that the
first chemicals to achieve this ability to copy themselves were strands of ribonucleic
acids or RNA.
The basic constituents of RNA, and DNA as well, are four different nucleotide
molecules. The compounds that nucleotides form have chemical affinities for one
another and they tend to group together creating long strands. The RNA world
hypothesis, a well accepted theory for the origins of earth’s first replicators, suggests that
these chemicals existed in small amounts near the bottom of the ocean and that, over
time, the long sequences of nucleotides developed a way to make identical duplicates of
themselves. Because the earth is such a dangerous place for large organic chemicals,
any RNA strand that could not duplicate itself would eventually be worn down or
destroyed. In a volatile physical world, rapid replication would have been the only path
that allowed these RNA strands to perpetuate themselves.
The way in which these first strands of nucleotides replicated was probably very similar
to the way that our DNA replicates itself within our own bodies. DNA replication is
achieved through the use of chemical catalysts called enzymes which travel down the
length of the DNA or RNA strand and duplicate it nucleotide for nucleotide. The enzyme
that our bodies employ to complete this task is called DNA polymerase. It is not clear
what enzyme was used by our oldest ancestors, but it was surely very similar to DNA
polymerase in structure and function. Luckily for us, the mistakes inherent in RNA
replication, also known as mutations, allowed these early replicators to be modified from
their original forms and to respond to the rigors of their environment.
DNA polymerase makes occasional mistakes, and often these mistakes are not caught
by the figurative spell checker, DNA repair enzyme. Such mistakes often have no
consequences for the organism. Sometimes they can be debilitating or fatal and at other
times they can be beneficial. When these mistakes prove useful they can help create
genetic variability in a gene pool and thus allow organismal populations to change with
time. Theorists believe that natural selection began to act on these RNA strands on the
bottom of the ocean, weeding out the poor or slow replicators and allowing the robust
ones to proliferate. After some time, competition for resources must have caused these
original replicators to develop new survival strategies.
It is thought that the environment drove these RNA strands to compete with one another.
For instance, a scarcity of resources may have caused these replicators to use
chemicals to destroy one another. If they were in fact successful at destroying other RNA
strands then they not only kept other strands from taking scarce resources but they also
had immediate access to a nucleotide corpse that they could use to create a replicate of
themselves. It is thought that this “chemical warfare” caused them to develop protein
enclosures to protect themselves from other strands and from the harsh environment.
Today, we know these protein enclosures as cells, the smallest units of life. These
simple cells changed and evolved to perform complex and meaningful functions, all of
which came about to protect the RNA (and later DNA), and to increase the productivity of
Some of the earliest replicators used cells as vehicles to replicate more successfully,
and it is obvious that we use our bodies (complex conglomerations of cooperating cells)
in much the same way. Put simply, our bodies are vectors for replication which grew
more and more complicated in response to intensely hostile and competitive
environments. But it is important to point out that genetic or behavioral complexity is not
necessary for successful replication. Not only are there far more individual bacteria on
the earth than there are individual humans, but bacteria also make up a larger proportion
of the earth’s biomass than all members of the human species combined. The
evolutionary success of both humans and bacteria shows that nature can allow a large
number of different reproductive strategies.
As reproductive strategies go, there seem to be two very successful kinds. One, used
by bacteria, is reliant on the transference of genes alone. The other, employed by
humans, is reliant on the transference of genes as well as the transference of memes.
Memes are units of cultural or social information and they are passed or taught from
parent to child. The human condition is reliant on memes- without language, knowledge
and skills humans can not survive on their own in a natural environment. Bacteria, plants
and many other organisms however have no use for memes. All of the behavior that they
need to reproduce is already contained in their genes and in their bodies at birth.
It is interesting to note that memes can be thought of as another form of replicator. Just
like genes they are passed from parent to child and usually only the ones that increase
survival and reproductive success are able to persist. It turns out that there are two
antagonistic strategies used by organisms to perpetuate themselves, one is the r
strategy and it is reliant on genetic transference alone and the other is the K strategy
which is reliant on both genetic and memetic transference. To learn more about the r
and K strategy continuum click here.
DNA Polymerase: noun
Any of a variety of enzymes responsible for replicating a series of nucleotides by using a
single stranded portion of DNA as a template.
A unit of cultural or social information that is transmitted by behavior or by observation. A
lesson that is transmitted from one mind to another.
The basic chemical constituent of DNA and RNA. A compound consisting of a
phosphate group and a nucleoside.
Parental Investment: noun
The transference of resources, protection, memes or any form of care from a parent to
Any construct that is able to reproduce or make copies of itself. Living organisms,
memes, computer programs, cellular automata all can be thought of as replicators.
|Organization for the Advancement of