How Did Life Appear on Earth?
And as an aside: why we prefer to live rather than die?
This page is part of my topics in
biology pages. For comments or
suggestions, email to the author.
It has long been suggested (since 1859) that
the existence of living beings on this planet 
you know, those wonderful
creatures starring in the documentaries of the Discovery channel,
filling our leisure time with awe and amazement is not due to
some capricious decision made by a supreme Designer, who, one day
thought "Let's make the Earth give forth plants and
animals". Instead, it was suggested that all species
(including Homo sapiens, members of which are the author of this page, and you, gentle reader) evolved
out of earlier ancestor species. Moreover so this theory goes all living creatures share a common
ancestor, and their evolution is determined by purely natural
mechanisms, not supernatural ones. Although scientists whose
purpose is to study these issues (i.e., biologists) show a nearly
unanimous agreement on the correctness of the general principles
of evolutionary theory, some laypeople are reluctant to accept
this idea. "What? We, the crown of Creation,
descended from monkeys?!" It is an appalling thought, to
many, to think that we might not have been specially designed by
an all-caring, loving, supernatural, and intelligent Designer.
So laypeople often think that, even if species
change throughout the millennia, such changes might have been
"helped", or "directed" towards a
predetermined goal at the right moment, by the Intelligent
Designer. Others refuse to accept the very idea of change among
species, in spite of the overwhelming evidence brought forth by
biologists, paleontologists, and geologists. "Anyway,"
say evolutionary disbelievers, "even if evolution does
happen, and species change through time, nobody can explain why
life exists on Earth in the first place. Who placed it here? Who
created the first living being? And who started off evolution,
knitting it in the fabric of biological life, so that it can be
discovered as a 'theory' in our times?" It is the purpose of
this text to show that there are answers to these questions. It can
be explained how life appeared on Earth. In a paradoxical manner,
evolution contains within itself the explanation for its own
existence. To understand it, one needs no special training, or
scientific knowledge, but mere common sense and rational
thinking. If you decide to read on, you may be surprised to find
out that the explanation will provide answers to other, seemingly
unrelated questions: why all creatures including the majority of humans want to live? Why no
animal ever chooses to die? And why, contrary to our
will, we die eventually?
Have you ever
entertained the thought that you might decide, for no reason at
all, to drop yourself under the wheels of a passing car? This
thought once crossed my mind but it wasn't because of depression psychologically, I am a
very balanced person. It just popped out of nowhere one day among
my thoughts, without warning,while I was walking along a busy
street. At once I felt very uncomfortable having such a horrible
thought in my mind, pondering its dire consequences for my
immediate relatives, and the people I love. Although human beings
are the only members of the animal kingdom who have the
"privilege" to be able not only to think such thoughts,
but also carry them out (under stressful psychological
conditions), no other living being seems ever to consider this
possibility: all creatures appear to be always striving to
survive.[1] Why?
In what follows I will attempt to show first
that life didn't spring out of nowhere on Earth, as a whimsical
decision of a Supreme Architect, but that it is a natural
consequence of the fundamental laws of chemistry. Nor is
evolution some special sort of "law" that was placed
upon biological life for unknown reasons; evolution is also a
direct consequence of the laws of chemistry. That is, given the
structure and properties of atoms and molecules, and certain
suitable conditions, evolution is bound to happen, just as rain
comes given suitable atmospheric conditions, without anyone
"ordering" it to drop on earth. A consequence of this
idea is that
assuming chemistry works the same way everywhere in the known
universe we should
expect biological evolution to appear or have appeared elsewhere in alien worlds, given the
right conditions. Notice that the claim is not that every
alien evolving biological system if any exists has to be using the particular mechanism through
which evolution was implemented on Earth, namely, our wonderful
DNA molecules. The implementation of evolution may differ in the
details from place to place, but the fundamental evolutionary
principles have to be the same. Along the way in our
discussion I will provide an explanation for why species want to
live and not die, and for why procreating, finding food, and
avoiding predators seem to be such all-important, life-long, and
life-consuming activities.
Let us start with a thought experiment. Suppose
we put a number of colored balls on a table, and shuffle them so
that there is no particular pattern formed by the colors. Figure
1 shows such an arrangement.
Figure 1: A random
arrangement of balls in motion
The balls keep moving randomly on the surface
of the table, jostling and bumping against each other. Now, my
plan is to have each of those balls represent a molecule for example, they could
be molecules of water, methane, ammonia, carbon dioxide, and so
on so I'll drop the
fancy term "colored ball", and call them
"molecules" from now on. Each color represents a
specific type of molecule. For instance, the blue ones could be
the water molecules; but we don't care really which color stands
for which type of molecule because we want to assume there are
several types (colors) and a fair number of molecules of each
type.
Imagine now that when our molecules bump
against each other chemical reactions take place. Some times the
blue ones join with the green ones and give a new color (a new
type of molecule), for example, orange; then the orange ones may
join with the yellows and break down in a specific way, giving
two different types; and so on. In short, chemical reactions take
place, causing the colors on our table to change continually,
with no apparent plan, no purpose, no design or pattern. If you
pay close attention to the molecules in figure 1 you'll see them
gradually changing color, after each collision. Notice, however,
that the reactions (color-changing) all comply with the laws of
chemistry. For example, a methane molecule and two molecules of
oxygen (say, one green and two reds) will always yield two water
molecules and one carbon dioxide (say, two blues and one yellow).
There is randomness in the collisions, but no randomness in the
outcome of a chemical reaction.
So our table-world goes on like this for quite
some time. Compound molecules tend to become more and more
complex, especially since one of the elements, the carbon
atoms, tend to cluster in "chains" and
"branches" of arbitrary length, allowing other
molecules to cling onto those branches. Colors come and go,
appear and disappear, new colors emerge which hadn't been seen
before, but no particular color "dominates" the others,
since each type of molecule has a random choice of possibilities:
either joining with others, or breaking down in some way, thus
yielding different colors on our table. The activity goes on for
a long time, and complexity in molecular structure keeps
increasing, until… one collection of molecular types makes
an initially inconspicuous appearance.
This kind of molecule,
which will be depicted in the figures that follow with hues of
purple color (and a little mark on the center, you'll see later
why), has a property that none of the other molecules had before at least not to such an
explicit degree: when a molecule of this kind reacts with other
molecules on the table, instead of breaking down in a haphazard
way, it makes a copy of itself. The copy is not perfect.
We'll show differences in structure between the parent molecule
and its copy as differences in purple hues. The point is,
however, that parent and clone molecule look very much alike, and
both continue existing and reacting after the cloning. There is
nothing miraculous in having a molecule cloning itself.[2] A molecule can "achieve" this by first
gathering various other simpler molecules from its vicinity, thus
growing in size. The growth in size causes some of the bonds
between its atoms to weaken, so when it reaches a certain
critical size it splits, and two nearly identical copies of the
original purple molecule are made. The two purple ones go on
gathering scraps of molecular debris from their environment (not
because they "want" it, but because this is dictated by
their chemical structure), and continue growing in size, just
like the original molecule did. When they have gathered enough
material they split again, yielding four purple molecules where
there had been only two before. This sequence of chemical
reactions continues for awhile, resulting in eight, then sixteen,
then thirty-two varieties of purple, and so on, with their
numbers increasing like this, "geometrically". Of
course, not all of them manage to complete their
scrap-gathering-and-split cycle, because they just don't happen
to bump against the right kind of scrap to add on to their
bodies, or they actually break down when they meet with a few
molecules that react by taking chunks out of the body of our poor
purplies (which thus cannot continue their normal chemical cycle
because their structure is altered). More important, several of
the clones are not faithful enough replicas of their parents, and
so are not capable of cloning themselves. A few of them, however,
can have even better cloning abilities than their
parents (just out of pure chance: a person can be taller than
both of his or her parents). Such "better replicators"
will tend to increase in numbers, precisely because they do a
good replicating job, at the expense of "worse
replicators", the population of which will tend to wither
away. It is those "good" replicator molecules that
contribute to the increase of the purple population.
Not very long after the appearance of the first
purple molecule, a dramatic change starts becoming evident on our
table: where there was no pattern before and colors were changing
randomly, now the purple molecules tend to persist as a color. A
glance at our table suffices to notice this change (see figure
2).
Figure 2: Purple
molecules prevail
But note that if
you view this figure a long time after the page was loaded, some
purple (replicator) molecules may have "mutated" and
taken on different colors. However, all replicators are depicted
with a little square in their center, contrary to other molecules
which don't have that mark. To start anew, reload the page.
What has happened? At the chemical level,
nothing really changed: just as chemical reactions were happening
before, chemical reactions continue to occur now. However, at a
higher level of description, which we call biological,
things started appearing that are worthy of new words for their
description. For example, it looks like these purple molecules
"want" to find scraps of smaller molecular debris
(shouldn't we call those "food"?) in order to grow and
eventually split in two, replicating themselves and starting all
over again. It's not that they really "want
food", of course
they're just molecules, after all, like every other type on the
table: every molecule or atom, no matter how simple, might be
seen as "wanting" to "eat food". For
instance, an ordinary atom of sodium may be seen as
"wanting" an atom of chlorine, to make a molecule of
salt. The same thing happens with the purple molecules: they
"want" the molecular pieces which they can bind with
(some of which, occasionally, break them down). But by virtue of
being the only ones which clone themselves, they appear as if
they succeed in increasing their population. Hence, the
population of purple molecules appears as if it wants
to keep existing and growing, at the expense of other kinds
of populations, which do not have such "desires"
because their molecules simply change randomly from one type to
another. Notice that now we can start talking about the whole
population "wanting" to do something (to exist), while
before we couldn't ascribe such an attribute to populations of
non-replicating molecules.
Thus, we started talking about
"collections (or: populations) of molecules wanting to
live". The reader might feel the verb "want" is
too heavily loaded with human-related values, and we are not
warranted in using it for collections of molecules. True, but is
there a line we can draw among animals and say that some of them
really "want", while others simply "react"?
Does a dog "want" a walk? Who can resist describing it
as volition when our poodle scratches on the front door at the
time of her afternoon walk? Does a parrot "want" to
detach the seeds from the bird-feeder? Does a shark
"want" to attack? Does a spider "want" to
spin its web? Does an amoeba "want" to engulf a scrap
of food, invisible to our eyes? Where do we draw the line? Maybe
the best strategy is to not draw any line at all, and allow such
words have a wide range of meanings, from the simple, to the most
complex. The advantage of doing so is that we don't have to
invent new words for the various shades, nor do we have to make
arbitrary decisions about where to draw the lines. Under this
scheme therefore, yes, a particular collection of molecules wants
to survive, wants its members (molecules) to find food,
and wants to do so at the expense of other collections.
Hence we come to a point where we can discern
the underpinnings of our most fundamental biological functions.
We want to eat and grow because our earlier ancestors (including
the earliest forms of non-living chemical compounds)
"wanted" to "eat" and grow. In an even more
fundamental sense, eating is none other function than the mere
binding of atoms and molecules. Whether it is hungry Joe
devouring a Big Mac, or an oxygen atom making covalent bonds with
two atoms of hydrogen, the principle is the same. Except that Joe
calls the satisfying of his needs "eating", while the
oxygen simply "binds" with hydrogen.
It's time to put these ideas together in a
program, similar to figures 1 and 2, but which you can interact
with. The program will start with a collection of molecules, all
of which will be "plain vanilla" (non-replicators), as
in figure 1. You can fill the space with such molecules by
clicking on button 
, at the top-left of the program's area.
Then, when you click on 
, the molecules will be set in motion,
starting to bump and react against each other, gradually changing
colors (i.e., their nature). The possible colors available to our
molecules are shown on the next figure:
Figure 3: Colors
(types) available to molecules
"Hue" = 200, on the
horizontal axis, means that the color is purple. "Sat"
= 236 (which stands for "saturation"), on the vertical
axis, means that the color is fairly rich in content (low
saturation, close to 0, means the color is washed out, or
grayish). Finally, "Lum" = 150 (which stands for
"luminosity"), on a separate axis on the right, means
the color is neither too bright (whitish), nor too dark
(blackish).
In figure 3 we see all possible colors arranged
in a square. A tiny portion of this square (very close to the top
line and on the right, within the area of purple color) has been
singled out with a little black rectangle, barely visible. Any
molecule the type of which belongs to that area, will be a
replicator. Initially, as we said, no molecule will be of that
type, but as they react by bumping against each other and change
colors, you can think of them as "moving" in the above
colorful square (this is a conceptual "motion", of
course, as opposed to their real motion in space). Thus, by
chance, a molecule while "moving" (changing type) in
the above square, may fall into the tiny black rectangle, and
thus acquire the property of replication. Once there, it may bump
against "food" while wandering in space, and thus grow,
split, and produce a copy of itself (another replicator), or it
may not find enough "food", bump against some
"poisonous" molecule and break down, becoming potential
"food" for others. Go on! Try the program.
As soon as you press
on Start, figures 1 and 2 will freeze, to free up computer
resources and make motion in this program smoother. They will
continue moving as soon as you pause this program.
You may have to wait for
some time before the first replicator appears. When I try the
program, I get the first replicator at any "epoch" (=
one step in space for all molecules) between 100 and 1000, but it
can happen really at any time, since the motion is random. You
can see the epoch number on the status line (at bottom), as well
as the overall number of common and replicator molecules.
Experiment by changing the parameters of the program (initial
number of molecules and and their size, which determines the
space size, accordingly), to see how the arrival of the first
replicator varies in time. Note that although the first
replicators will look like this 
, soon some of them will "mutate" (the
copied version will be imperfect, hence slightly changed in
type), and so various strains of colors will appear all discernible as
replicators through the tiny black rectangle in their center. A
few of those strains will be better survivors than their parents
(e.g., because they are a little more resistant to poisons and
thus last longer before breaking down, or because they can
consume food a little more efficiently, and so on). So, over
time, you'll see those strains, having a survival advantage, to
dominate in our space, before being surpassed by even better
survivors, etc. Once again, all this will not happen because they
"want" it, but because it is dictated by the statistics
of their chemical nature. There is nothing in the code of this program that dictates replicators to live longer. All each
replicator in this program has is a copying fidelity factor, an
"endurance", and something like "enough food in
order to split" factor, all three of which are a direct
consequence of its type.[3]
How many can the replicator molecules become?
Can they "eat up" all other molecules, thus turning
everything into a replicator? If our space has borders, as most
real spaces do, this is not possible. The reason is that the
supply of "food pieces" (non-replicating molecules) is
not unlimited. Sooner or later the food pieces will start
becoming sparse, and the replicator molecules will not be able to
"eat" anything: they will start drifting aimlessly for
some time, until they bump into some dangerous substance (some
special "poisonous" molecule, replicator or not) and
break apart, making a few chunks of "food" for other
replicators with the pieces of their bodies. Eventually the
numbers of the two categories (replicators and plain molecules)
will come to a balance point. With the default values for the
parameters in the program above, I observe a balance at around
780 replicators and 220 plain molecules.
We are ready now to answer the question posed
by the title of this page. Why we want to live?
Why does any animal, or plant, or bacterium, or
any species at all, want to live? Could we find the answer by
thinking about our collections of replicator molecules? Do they
want to live?
Consider what would
happen if any one of the replicating varieties had the tendency
(by a hard luck due to a mutation in its chemical structure) to
break apart while growing before maturing to the size that is
critical for splitting. Such a hapless individual would not
produce descendants. Which means that the deleterious
mutation that led to its formation would result in an individual
incapable of self-replicating, and that would be the end of the
story and of the
mutation. Only mutations[4] which allow the
individual to split can be carried over to its descendants, and
hence, get propagated to future generations. Therefore, the only
individuals which manage to form viable populations are the ones
which live to reproductive age. For our molecules,
"living to reproductive age" means growing to the point
of reaching a critical mass, and then splitting. So the
"desire" to live, at least up to reproductive age, is a
necessary built-in feature of all survivors. The only creatures
which are not interested in living are the ordinary
non-replicating chemical molecules.
Fine, but do animals live only to reproductive
age? That is certainly not true: animals (and plants) don't die
immediately after giving birth at least not the ones we are most familiar with.
Furthermore, we know from personal experience that we humans do
not give up the desire to live right after the birth of our
children. How can the "desire" of the purple molecules
to live to reproductive age ever be compared with our desire to
live forever?
And yet it can, because the difference has to
do with biological complexity. Along the path that connects us,
monstrously complex mammals, with them, simple first invisible
replicators (a path than extends for at least 3,700,000,000 years
to the best of our knowledge), some changes occurred. One of them
was the "discovery" of sexual reproduction. Until
around 2,100,000,000 years ago, all species were replicating just
like our purple molecules: by splitting. Somewhere at that time,
give or take a few dozen million years, a new mode of
reproduction appeared: replicating by combining genetic
information (that is, molecules) from one "male" and
one "female" individual. Why? For the same reason all
innovations appeared in our multi-billion-year evolutionary
history: because it offered advantages in survival. We do not
need to go into details here, explaining what those advantages
are. Suffice it to say that what is involved is not the survival
of individuals such as me and you, but of the genes
(molecular chunks of information) that we carry and want to
transmit to future generations. The story of gene replication and
propagation is a very important one, and we'll need to understand
it in order to be able to appreciate the answers to questions
such as the one posed in this text. For now, however, it's
sufficient to observe that humans (and many other species) do not
produce clones of themselves by splitting in two like the
original replicators, but make children by combining genes from a
female and a male. Thus, we do not cease to exist immediately
after giving birth, for various reasons. For one, we may give
birth to more descendants later, and that means making more
copies of our genes. For another, we need to take care of our
children, making sure they'll live well and produce their own
offspring (thus furthering the lineage of our genes). And even
long after reproductive age, our existence may prove useful to
our offspring by taking care of our grandchildren, a
practice which is common among social animals, such as humans,
chimps, and gorillas. Hence, we don't want to die, ever. Many
other animals do not live much longer after giving birth. (Some,
like the Alaskan salmon, die right there, on the spot, after
reproduction.) But if any living being ever wanted to die before
passing on its genes, neither itself, nor its descendants can be
among us to witness their existence.
Let us keep thinking a bit on this point,
because with what we have observed so far we can see the answer
not only to the question "why we want to live?", but
also to the one asking "why we die?". Here is why we
eventually die, in spite of all desire to live forever.
We noted that of all mutations that happen to
molecules when they replicate themselves, those that are
beneficial for the molecule's survival are bound to be propagated
to its descendants (because they result in better survivors),
while those that are detrimental and show their bad character
before the molecule clones itself are bound to be eliminated
(because molecules of such nature will not replicate, or will
replicate erroneously, resulting in non-viable populations). But
what about those mutations which are detrimental but do not show
their effects until some time after the molecule's
reproductive age? There is nothing in what we've seen so far that
labels such mutations as "bad": they may result in
"killing" the molecule at a later stage, but it first
manages to produce descendants, all of which will carry such
"killer mutations" (being copies of their parent),
which will not affect their ability for procreation! And so,
"killer mutations of old age" will keep accumulating in
all strains of replicators.
Did the word "cancer" appear in your
mind while reading the above lines? Tumors are a very complex
phenomenon, not yet properly understood, but their appearance
complies to the same basic outline, as expressed in the previous
paragraph.
I once had a cousin, one year younger than me,
who died of cancer at the age of nine. A couple of years later,
another cousin of mine, and best friend of my childhood, died of
an aneurysm in his brain at the age of thirteen. Those losses
were devastating to me and my relatives, and I couldn't swallow
in my child's mind the idea of "what kind of cruel God that
is, who lets innocent children die". Little did I know that
God whether existing
or not does not have
to be part of the picture, nor does any god have to be accused of
the fate of individuals. It's all statistics. We all have those
"bad genes" in our bodies. Their effects are usually
expressed gradually, and cumulatively as we age, both in mild
forms (freckles on the dried, wrinkled skin, accumulation of
salts in the joints, blocking of the arteries, etc.), and in more
severe ones (tumors, Parkinson's and Alzheimer's diseases, heart
attacks, and many others). Generally, however, and fortunately! children do not develop
tumors nor degenerating diseases. In the very unfortunate case
where they do (because statistically even the worst kind of luck
is bound to strike a small enough number of individuals), they do
not live to reproductive age and do not pass their unfortunate
luck to any descendants. The rest of us carry on our (accumulated
through billions of years) bad genes, which express themselves
seemingly "conveniently" long after we give birth to
our children, and after we ("conveniently", again) are
given some time to take care of them, and make sure they live
well and prosper.
The reader may now object with this logical
argument: why didn't evolution "take care" of bad
mutations? Wouldn't it be beneficial to individuals to go on
living forever, and be able to keep on producing descendants at
regular intervals? Wouldn't that strategy result in even more
viable, impossible to eliminate populations? Why didn't such
bad-gene-free populations ever appear?
The result of living
on forever would be that the number of individuals of a given
species would keep on increasing. But is this possible? After the
number of individuals reaches a maximum value, food in the
environment is repleted, and members of the species start
starving and die. (See how this happens to the various colored
types in our program, above.) So the number of individuals gets
checked by the availability of resources in the environment.
There is no built-in evolutionary principle that says "we
have to have as many individuals of our species as
possible". All that there is, is that species which are
better equipped prevail, purely statistically, over
their competitors (and that's a mathematical certainty, not a
"law" of nature which we observe but we don't know why
it's here). That's all. Thus, what appears to us, personally, as
"a good thing to have" (i.e., living forever), is not
something derivable from the structure of the material we are
made of. Living forever would be something we would expect from a
Designer to grant us, if such a creature had actually designed us
and cared for our well-being, for our fear of death, the sorrow
we feel for our deceased loved ones, and so on.[5] But instead of being made by a Designer, we sprang out
of the un-caring, un-planning ahead forces of nature. Evolution
doesn't have any provision to look ahead and plan for the future,
nor sense our desires and satisfy them. It's a blind natural
mechanism that makes use only of what works here and now. In all
fairness, evolution did make us, large mammals, to be
able to live long after we give birth to our children, and take
care of them. Most other living beings don't have this luxury.
But those "bad genes", the little time-bombs waiting to
explode in time as we age, were there from the beginning, never
completely eradicated by evolution because the current scheme of
things works (as far as propagation of our genes to our offspring
is concerned). So we die.
I would like now to go
back to a point, which the reader may consider as very crucial,
because most of what we have seen so far rests on it. The reader
might object like this: "You have attempted to explain how
life appeared on Earth by postulating the existence of a first
replicator. But how could the first replicator arise? Out of
chance? That would be like winning in a lottery where your
chances are one in a trillion, or who knows how much less. You
have pushed the appearance of life back from the first living
being to the first replicator molecule. That doesn't explain
where the first replicator came from."
But wait! This objection accuses me wrongfully
of things I never said. There was no first replicator.
What this means is that "replicating" is not a
black-and-white, all-or-none property, that molecules either have
or not. There can be shades of gray in-between the range. At one
side of this range stand molecules which, after reacting and
breaking down, result in pieces that do not look at all like the
original ones. Most inorganic molecules belong to this side of
the "replicating range", i.e., they are clearly not
replicators. As we move on to organic[6] molecules
though, whether a molecule "replicates" or not is not
so clear. First, we are not talking about a reaction which is
completed all in one step. As mentioned in the first paragraphs,
such a molecule can accumulate pieces of "scrap"
(smaller molecules) on its body in several steps (several
reactions), growing in size. This growing makes it unstable,
until at some point the internal bonds that hold its atoms
together break, and several pieces result out of this final
reaction. Now, there might be some pieces (more than one) that
look a bit like the original molecule that started this series of
reactions. How much any of these pieces looks like the original,
determines how good a replicator the original molecule is.
"Looking alike" is not a true-or-false property.
The program presented earlier in this page
starts with a replicator that is not good at replicating
at all: very soon after it appears it mutates to other types,
which may or may not be replicators. Only the few decendants
which, by chance, happen to be even better replicators
will keep and in fact improve the "replicating"
character, and the best of them will produce viable populations.
This is why, if you let the program run for awhile, the original
purple hue soon gets replaced by different ones.
What do we know
about such possibly-replicating-but-not-quite molecules? Not
much, yet. No biologist, or chemist, has so far succeeded in
proposing a molecule, other than our familiar DNA and its ken,
which can be characterized as a replicator,[7] of the kind that would lead to terrestrial life. Why we
would be interested in a molecule other than DNA? Because the DNA
is already fairly complex, and we assume that itself is the
product of evolutionary change. DNA, together with its
counterpart, RNA, are probably the lone survivors of a long
history of "struggle" among replicators and
near-replicators. How do we know this? DNA and RNA cannot
replicate by themselves. They require the existence of certain
proteins in their environment. However, those proteins can only
be manufactured in the presence of molecules such as DNA and RNA.
Here we have a chicken-and-egg problem: neither DNA, nor the
proteins could have appeared first, because the one requires the
other. The only possible answer to this problem is that what we
observe today is the end-product of a long chain of changes. In
the beginning of this chain must have been molecules that
replicated in the simple way we have already outlined
(accumulating, growing, splitting). Somewhere along this chain
there appeared substances that started "cooperating"
with each other, not because they "wanted" it, but
because this cooperation resulted in more viable populations,
hence the cooperating character persisted. The evolutionary
end-product of such cooperating couples is DNA and the proteins.
By the way, cooperation is not something unique to this case. It
appears over and over again as a theme in biology. Each one of us
lives because of such cooperation, too: mammals, including
people, have certain bacteria in their intestine that help in
digestion. Bacteria are complete and usually autonomous
organisms, and although invisible to the unaided eye, they are as
valid "living beings" as any other. If such bacteria
were removed from our intestines, we would die. But those
bacteria, too, cannot live anywhere else but in our
intestines. We thus have a simple example of cooperation between
organisms here, one which is called symbiosis. Probably
the most primitive example of symbiosis is the DNA-proteins pair.
Whatever has existed prior to this end-product must have been
significantly simpler. Still, it was evidently complex enough to
escape identification by contemporary science. There is a reason for
this: on the one hand, the majority of biologists do not work on
the subject of the origins of life.[8] On the other hand, the majority of chemists and
molecular biologists
who are better suited in pursuing the discovery of replicator
molecules are not
interested so much in the beginnings of life either, which they
regard as rather remote from what is commercially useful today.
So there is only a small number of scientists who work directly
in this area. Only time can make up for the insufficient
scientific activity on this subject.
Why we don't see
replicator molecules being produced spontaneously today, if this
was possible four billion years ago? Because the necessary
conditions that existed in a primordial Earth, when the relevant
reactions were taking place, are not in existence today: the
present terrestrial environment is vastly different, and it
doesn't support the (re-)birth of life. Neither was the
environment four billion years ago supportive of the present forms
of life. Suffice it to say that if we could somehow miraculously
be transported on the surface of our planet at that time, we
would die of asphyxiation. Living organisms have modified
drastically the earthly environment; as a result, what was
possible four billion years ago is not possible now.[9] Besides, even if a chemical reaction takes place today
that might lead to potentially replicating molecules somewhere in the vastness
of our planet's environment, away from curious scientific eyes it is very likely that
the resulting potential replicators become a nice meal for those
who have already mastered and perfected the replicating art
(e.g., bacteria). The "replicating niche", or, in other
words, the "super-niche of biology" on this planet is
already taken.
Footnotes (Clicking on the
footnote-number, on the left, brings back to the text. )
[1] It was brought to my attention that some cases of
animals committing suicide might exist. For example, dogs or cats
letting themselves die after the death of their owners; or
dolphins, committing suicide in captivity (see this page).
Such cases are possible, and show that the line that separates
psychology from biology is not a hard and crisp one, separating
our species from the rest of the animal kingdom. Other cases,
however, such as bees dying to protect their hive, lionesses
dying to protect their young, etc., are all explicable with
reference to the idea that what matters is the propagation of genes,
not the survival of the individual a
point that will be further explained later.
[2] We already know at least one self-replicating molecule:
it is the DNA (or rather, the DNA + proteins please read further in the text). So there is no doubt
about whether a replicator molecule can ever exist. The DNA,
however, cannot be the very first replicator molecule that
existed, because it is already quite complex. To see how simpler
replicators may have emerged on Earth, please read further in
this text. (If you want to go there now, click here.)
[3] If you're looking at the code of this program, check methods PhenotypeFromGenotype(), and React(), in
Molecule.java. If you are a programmer, feel free to
"mutate" the code in any way you like, adding your own
copyright comment and retaining the original one(s) as a courtesy
to the original author(s).
[4] Notice that here I use the
word mutation as a synonym for gene. Although
this is incorrect, it is unreasonable to expect that the earliest
replicators which we refer to in this text would have employed
genes (collections of molecules "coding for" properties
of an organism) as we know them. So I'll keep using the word
"mutation" to refer to an imperfect copy of the
original replicator.
[5] I am aware of the fact
that religions such as Christianity, Islam, and Judaism, teach
that our "souls" keep existing after the death of the
body, and thus, according to them, God has actually seen it that
we, human beings, live forever. Another point of view, which I
espouse, says that such beliefs are the natural reaction of a
creature (humans) who was the first and only one to have the
cognitive ability to project the present into the future,
conclude that death is unavoidable, be scared of it, and develop
various cognitive defenses against this fear. The most effective
such defense seems to be the belief that some part of ourselves
keeps living after death. Such beliefs are understandable, but
ultimately baseless: there is nothing in the real world that
supports them, save for our own fears. I am of the opinion that a
better understanding of the real world in which we live helps in
alleviating such fears, giving us a proper perspective of our
place in the cosmos.
[6] "Organic" means simply that the molecule
contains one or more atoms of carbon.
[7] This is not entirely true.
In 1861, the Russian chemist Alexander Butlerov described the formose
reaction, in which a solution of formaldehyde and sugars
(both simple organic compounds) results in the multiplication of
the sugars at an accelerating rate, in a process known as autocatalysis.
More recently, in 1986, the first artificial replicator not
needing enzymes for its replication was synthesized by K. von
Kiedrowski.
[8] It's not because they
don't like the subject, but because there is a large gamut of
interesting topics in biology, all of which are actively
explored.
[9] The same explanation
applies to every instance of evolutionary change: no species may
"reappear" as the product of evolution because the
conditions that led to its emergence were unique, in every case since environmental conditions are at a constant flux
and never repeat themselves down to the last detail.
Further Reading Please
Note: jumping to external links causes Internet Explorer 5 (but
not Netscape 4.x) to stop the applet; you'll have to restart it
in case you are running it now.
Richard Dawkins, The Selfish Gene. Oxford
University Press, Oxford 1976.
Richard Dawkins, The Blind Watchmaker. W. W.
Norton & Company, New York 1987.
Daniel Dennett, Darwin's Dangerous Idea.
Penguin Press, London 1995.
Scott Freeman and Jon C. Herron, Evolutionary Analysis.
Prentice Hall, NJ 2001.
John Maynard Smith and Eörs Szathmáry, The
Origins of Life. Oxford University Press,
Oxford 1999.
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