MANY PATHS, ONE HORIZON
The story of mankind's spiritual awakening,
and of the part we play in it.
© Kit Constable Maxwell
2. EVOLUTION OF LIFE
~~~~~~~~~~~~~~~~~~~~~~
In 1953 the Chicago scientist Stanley Miller created a small enclosed
model of a primitive and sterile planet Earth. The ground he made
of primal rocks, and the air space he filled with hydrogen, methane
and ammonia to reflect the prevailing conditions of 4bn years ago.
He then introduced electrical discharges to represent lightning,
and in fulfilment of his wildest hopes the experiment produced an
abundance of amino acids, the primary component of the proteins that
comprise living cells. This major discovery firmly established the
principle of a self-originating life-form emerging out of the primordial
soup of the planet's primal resources.
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A lightning strike can
discharge a current
of
20,000 amps and
generate a temperature of
30,000 degrees Centigrade |
This explanation of the birth of life has held good
for forty years and is still widely accepted. Today scientists are
examining the molecule RNA (ribonucleic acid) which can develop, evolve
and subdivide itself in a manner that would have empowered the nuclei
of developing cells even more rapidly in those inhospitable days of
Earth's first billennia. RNA translates DNA (deoxy ribonucleic
acid) into proteins, while DNA is the control unit that governs
the code for genetic inheritance.
* *
*
The Earth and its Moon were formed around 4.5 billion years ago.
For the next half billion years the planet was bombarded relentlessly
by meteors, asteroids and comets, crunching into the surface like
multi megaton bombs. Some meteors were as big as Africa or Australia,
and the fantastic energy released would boil whole oceans and fill
the atmosphere with steam and detritus for centuries - obliterating
both light and heat, and destroying all life forms in their wake.
It is now believed that primitive cell life developed, evolved and
expired many times before finally succeeding in colonising the planet.
Concurrently, however, in the depths of the deepest oceans, protected
from the celestial bombardment on the surface and warmed by hydrothermal
vents in the ocean floor, other plant life was struggling to develop
and survive. Amazingly these early life forms continue to this day,
and modern sub mariners have recently discovered new and unknown life
forms in the sunless gloom at huge depths, which are supplying invaluable
information for mankind's insatiable interest in his primordial past1.
1 In 1994 an Anglo/Russian research ship equipped with a deep water bathyscaphe set out from Southampton to research these extraordinary life forms still surviving from the dawn of history.
EARLIEST FOSSILS
Some of the oldest rocks in the world, the sedimentary rocks from
Greenland, reveal traces of the very earliest plant cells known to
mankind, some 3.8 bn years old. A relatively short time later, from
3.5bn years ago, the world's first known fossils appear, featuring
primitive algae which are almost identical to algae occurring in Australia
today.
From 3bn years there followed a prolonged period of cell and plant
development evolving into photosynthetic organisms producing, for
the first time, oxygen. By 2bn years the earth's atmosphere was oxygen-enriched,
the asteroid bombardment had abated and conditions were slowly becoming
agreeable to developing life forms. By 1bn years the first multi-celled
seaweeds had become established, to be followed shortly afterwards
by the profoundly important development of mobility, when primitive
life forms learned to vacate their chance dwellings and set off to
choose their own. These adventurous semi-animals included jelly fish,
starfish and sea urchins, and later trilobites, crustaceans and other
exoskeletals.
At ½ bn years ago, the first sharks roamed the oceans while amphibians
and early reptiles were emerging from their aquatic domain, together
with marine plant life, and beginning to colonise the untenanted expanses
of dry land. Evolution gained momentum; small reptiles grew bigger
- Pterodactyls learned to fly, a momentous achievement that still
eludes humans 200m years later. Big Tyrannosaurus Rex began eating
his neighbours and grew bigger still, while Brachiosaurus remained
vegetarian and outgrew them all. At over 75 tons this veritable monster
of unbridled evolution staggered around the world, the greatest tribute
to the success, imagination and perseverance of all those dedicated
RNA's, DNA's and primary cells of 3 billion years before.
MIGHTY MATE
Had evolution got out of control? A monster without a brain wasn't
going to achieve much, save to get bigger at the expense of his environment.
The pace was appearing to have escalated beyond reason; Stegosaurus,
the great lumbering, 7m herbivore, was steered by a diminutive 3cm
brain, less than the size of our little finger. Some dinosaurs did
better than this, but these voracious and often oversized reptiles
were soon to become a victim of their own success. Brachiosaurus had
reached the point where the increasingly fertile soil, born of generations
of primal plant matter (now our fossil fuels) couldn't support his
monstrous weight. (Many ended their days stuck fast in mud). The trees
couldn't grow leaves fast enough to feed him, and the problems of
sexual encounter with his mighty mate amounted to a coupling courtship
of thrashing limbs with a combined weight of 150 tons. The damage
to their environment would have been severe, while the damage to each
other might have been fatal.
The dinosaurs lived from 215m to 65m years ago, a long span unparalleled
by human standards2, during which great variety marked the march of
selective evolution both in plant, marine and reptile life. Trees
developed from primitive algae, and birds developed from the dinosaurs,
(their scaly legs testify to their reptilian heritage). And then the
dinosaurs' 150m year reign came to an abrupt end during which almost
every one became extinct.
2Modern mankind's brief history of half a million years (from Homo Sapiens) is dwarfed by the dinosaurs' unbroken reign of 150 million years.
The reason was probably due to climatic changes, which could have
been triggered by a giant comet or by some great, errant asteroid
the size of a mountain, crashing into the planet and releasing such
a dense cloud of cosmic dust and steam as to obliterate the sun for
over 100,000 years, thus plunging the world into an unsolicited and
fatal ice age. Most plant forms survived, particularly those protected in an aquatic
domain, and so did many fish, notably the sharks. But the great dinosaur
era was over - and only the crocodiles (unchanged for 200m years)
and larger reptiles of today remind us of that great, top heavy age
of our extraordinary evolutionary heritage. DARWIN
The world was now 4bn years old; life had started, proliferated and
stalled. We still had no apes, no humans; Darwin's theory of evolution
had a long way to go to prove itself. Natural selection respects the
genetic changes inherited by life forms who are readily adapting to
their chosen environment. Thus fish turned into amphibians, who then
turned into reptiles, who turned into birds. Each step reflected the
inclination of its precedent, and this precedent was inherited and
mutated through the evolutionary process. Those who failed to evolve,
generally, failed to survive, although there are notable exceptions
to this, especially in the insect world, where ants and bees, for
example, survive almost unchanged to this day.
Natural Selection, or 'who dares, wins', was the basis of Darwin's
1858 thesis. It caused an uproar in his Victorian England among those
god-fearing Christians who wanted to believe, as a dwindling few still
do, that life began in a sun- kissed Garden of Eden, with Adam and
a somewhat wayward Eve living off a diet of apples.
The long gaps in our fossil records leave many unanswered questions
in mankind's ancestral lineage - but the evidence tells us that those
primitive cells of 3bn years ago had spawned sophisticated oxygenating
plants by 2bn years, primitive animal life by 1 bn years, then sharks,
coelacanths3 and other sea creatures by 500m
years, and overgrown dinosaurs by 200m years.
3The Coelacanth is a very early descendant of the Lobefin genus, ancestor of all land animals. Believed extinct for millions of years, they were rediscovered in 1938 in deep water off Madagascar.
MAMMALS
Dinosaurs and reptiles were, curiously, ill equipped for their changing
environment where heat and cold alternated faster than they could
respond. The earliest signs of the hot blooded, multiple heart chamber,
fur covered creatures we now call mammals began to develop during
the Jurassic (dinosaur) period but it was not until 75m years ago
that this genus generally began to expand and proliferate. Mammals
were viviparous, bearing live young rather than adopting the egg laying
medium chosen by reptiles. Rabbits were among the first of this new
life form and have been a very successful species ever since; rabbit
fossils have been found which are over 35m years old. Many diverse
forms of mammal then evolved, and preliminary distinctions may be
made simply on the basis of the subject's footwear. Hoof, paw and
claw distinguish the sub species immediately as a grazing, gathering
or predatory mammal, and illustrate Darwin's theory of Natural
Selection, equipping each species with beneficial and continuously
changing physical attributes as variously required by each to master
and survive its changing environment. The giraffe is one of many mammals
to illustrate this feature, having the same number of vertebrae as
all other antelope, yet managing to sustain an enormous elongation
of his basic structure to provide for his predilection for treetop
fare.
ANCESTOR
By around 50m years ago our ancestor, the wide eyed, short snouted
lemur had arrived, complete with stereo vision and grasping hands
- a small, nimble, tree dwelling primate who was busy developing unprecedented
manual skills in pursuit of his insectivorous and frugivorous diet.
Long ages were still to pass before the first fairly unmistakable
monkey appeared at around 30m years ago. This was Pliopithecus, a
small primate who had the unmistakable finger-and-thumb hands of the
genus, and like the lemurs of the old world4 still sported a tail,
which he used in balancing and climbing.
4The Old World describes Europe, Africa and the Easter hemisphere. The New World refers to the Americas and the Western hemisphere
The diminutive Pliopithecus was the direct ancestor of mankind -
and in the ensuing 30m years his line branched into the six distinct
sub species we recognise as our animal kin. First came the gibbons,
(20m years ago) with their flatter noses and long tails; then came
the now tail-less orang-utan (15m years) who were to be followed by
gorillas (10m years) humans (at 7m years), pygmy chimps (3m years
ago) and finally common chimps (at only 1m years ago).
DNA CODE
Religious leaders used to discourage the belief that humanity is merely
another ape species. It conflicts with traditional stories of creation
and our sense of dominion over the animal hierarchy. But the proof
of inheritance lies unchallenged in new skills of genetic identification.
DNA, the code for genetic inheritance, shows that monkeys and mankind,
predictably enough, originate from the same family, share the same
instincts and developed along comparable lines. However the relationship
between humans and gorillas is much closer than that of monkeys, sharing
almost 97.7% of identical DNA. Our relationship to chimps is even
closer, at a finger tingling 98.4%. In that last 1.6% lies the whole
extraordinary power of evolution that has set us aside so distinctly
from our hominid brethren. DNA CHART - Our relationship to the Apes
| Pliopithecus |
30m years ago |
DNA count % |
| Gibbon |
20m |
95.1% |
| Orang utan |
15m |
96.4% |
| Gorilla |
10m |
97.7% |
| Human |
7m |
100.0% |
| Pygmy chimp |
3m |
98.4% |
| Common chimp |
1m |
98.4% |
|
Table showing the time
that each species made the break away from
our common ancestor Pliopithecus, and the proximity
of our
genetic relationship expressed in percentage of DNA. |
CATASTROPHE
The story of evolution is all about invention, modification and adaptation.
And it's about extinction too, on a massive scale. Over 90% of all
life forms that ever existed have lost the struggle for survival and
died their unlamented death - a fate statistically likely to befall
humankind. Evolution hosts a catalogue of triumphs and catastrophes.
The major evolutionary achievement of humans, the great hairless ape,
is but one of the many miracles of development since life first established
itself on Earth. The full impact of our long history comes into perspective
when we examine the human embryo - to find it still starts life with
gills and tail, the reptilian hallmarks of our humble heritage. As
the baby grows so do a pair of muscles, lodged on either side of our
lower spine, that once wagged our now extinct tail. Informed scientists
trace the original ancestry of all mankind to the earthworm order
Annelida, who display gill characteristics common to those found in
the human embryo. This earthy fact, as much as anything else, tells
us of the great gulf that lies between what we know and what we don't...
like what lies ahead for us in the next phase of our evolutionary development.
