From: Glenn Morton (glennmorton@entouch.net)
Date: Fri Jul 18 2003 - 13:19:53 EDT
A few years ago I published an article on phylum evolution:
Morton, G. R. (2001) Transitional Forms and The Evolution of Phyla.
Perspectives on Science and Christian Faith, 53(2001):1:42-51
http://www.asa3.org/ASA/PSCF/2001/PSCF3-01Morton.html
At the end of that article, I had listed the predominant suggestions for the
cause of the Cambrian explosion. None of them seemed to explain everything.
Recently, there has been a novel proposal for the cause of the Cambrian
explosion, which I wish I had known of prior to that article's publication.
This hypothesis, does explain all the facts of the event. Andrew Parker, an
Oxford University zoologist, suggests that the cause of the Cambrian
explosion is the evolution of the image-forming eye. I suspect that this
view will gain currency among paleontologists.
to understand this, consider what life would have been like for eyeless
precambrian animals. They would have lived in a world of darkness. The
only sensations would be touch, taste, hearing and smell. The only light
sensitivity might well have been light sensitive patchs which didn't form
images. But these animals were probably too primitive to have good hearing
so life mostly consisted of touch, taste, smell and the detection of light
and dark only. They would get their food via accidentaly bumping into it.
But, their predators would also have to find them by accident. This would
mean that there would be no need of camouflage, or the evolution of
coloration. Why spend energy on maintaining a camoflage defence system when
there would be no one who could see it.
Parker, says:
“More obviously, the shape of an animal is an important component of
camouflage and mimicry. The stick and leaf insects, and weedy sea dragons,
must possess the colours and shapes of sticks, leaves and sea-weeds
respectively. The movement of these animals is just as vital. The praying
mantis that mimics leaves must sway in the wind just as the leaves around
does.”
“These are physical and behavioural adaptations to light. Light not only
affects the colour of an animal but its whole form and behaviour. Remember
that if an animal is not adapted to its light environment it will not
survive. Now we can see that this rule calls for real responses throughout
the evolution of species. It is not enough for a lioness to have beige
pigments that allow it to blend into the surrounding grass. The lioness
cannot evolve the contours of its environment so it must possess another
weapon to enable it to catch food—it must be capable of keeping a low
profile, not unlike a military sniper.” Andrew Parker, In the Blink of an
Eye, (Cambridge: Perseus Publishing Co., 2003), p. 106
“It is interesting that on land the same physical environment exists at
night as it does during the day. Trees and rocks continue to provide nooks
and crannies…but no longer areas of brightness and shade. And the
evolutionary outcome? There are considerably fewer species active at night
compared with the day. There really are fewer niches—‘ways of life
’—available at night.” Andrew Parker, In the Blink of an Eye, (Cambridge:
Perseus Publishing Co., 2003), p. 119
Nighttime on land is only a step towards life in total darkness. He
continues:
“Below 200 metres, many animals are red. The light here is blue, and only
blue. The lack of red light means that red pigments have no chance to
reflect. Instead they absorb the blue light and so appear invisible. Red is
a good camouflage colour in the deep.” Andrew Parker, In the Blink of an
Eye, (Cambridge: Perseus Publishing Co., 2003), p. 104
Now, Parker reports the discovery by Jim Lowry that evolution slows to a
crawl as one goes into the darkness. The SEAS project studied isopods on
the Australian coast. There were hundreds of species in the bright, shallow
waters. Some of the species differences were minor. But as one went deeper
into the seas, thus into the dark, the diversity of species declined
significantly. Below 200 meters there was bathynomus alone. Bathynomus was a
half-meter long isopod resembling monsters from the movies. When the
researchers compared the Bathynnomus with isopods found in the deep waters
off Mexico and India, they found that they were nearly identical. What was
most interesting was that this animal had barely evolved for the past 160
million years. Evolution was going forward at a snails pace in the dark.
This set Parker off thinking about why the speed of evolution goes so slowly
in the dark. And that lead to checking out the life in caves. Animals
living in caves lose all coloration, lose their eyes and find food by
bumping into it, and sensing it with sound, touch, taste and smell . This
was a clue to what eyeless life would be--no camouflage, no color and few
species.
But, when the first animal developed the image-forming eye, all things
changed. When a predators forms your image on his retina, what happens next
is a life and death issue. The predator can now see not only your shape, but
your behavior as well. He can begin to calculate your speed, where you will
be in 5 seconds. It is vitally important that you SEE him or at least have
camouflage enough so that he can't see you.
This sets off an arms race of biblical proportions. The prey must develop
colour which can't be seen (or more correctly, those who by chance have
coloration which protects them live, those who don't, die). There is
selective pressure on animals who can sense light and dark to evolve those
light-sensitive patches into image-forming eyes. To see a dark shadow of a
predator is better than not seeing it at all. But to see a predator at a
distance before he casts his shadow over you is even better.
Parker then went and checked out the eyes on fossils from this time. What he
found was that animals after 544 million years ago had eyes. Before that,
they didn't. He writes:
“Between 544 and 543 million years ago a revolution took place. During this
one million year period, vision was born.
“We are now in a position to interpret the statement ‘How ancient already
in the Lower Cambrian must the compound eye have been’ made by Frank Raw.
Yes, the compound eye and vision were well developed in the Lower Cambrian.
But no, it was not ancient—it was contemporary. And it became the new
fashion.” Andrew Parker, In the Blink of an Eye, (Cambridge: Perseus
Publishing Co., 2003), p. 228
When Cambrian predators, like Anomalocaris, began to swim the seas, SEEING
their prey, the world changed. Animals had to develop the armoured
protection of shells and spines. Those animals without them, were easy
pickings and they died. Coloration in the form of diffraction gratings on
those shells first formed at this time (p. 184). Light opened ecological
niches into which animals rapidly evolved. Color differences alone were now
were enough to reproductively isolate animals in a visual world. Niches
proliferated, hard parts proliferated, all because the world could now see.
The phyla existed long before the Cambrian, as is shown in my article. What
changed at the Cambrian was not the sudden appearance of new creatures but
the sudden armoring of pre-existing phyla cause by the fact that predators
now could strike with precision. Eyes were the laser-guided attack weapons
of 545 myr ago.
The interesting thing about this concept is that it does answer the
questions and fit the data. It explains the slow evolution of life for
nearly 3 billion years. It explains the hard shells. It explains the
'sudden' development of new species. It explains the 'sudden' appearance of
phyla. It explains why the world of anmals changed so radically that the
rocks which were being deposited at that time, split geologic history in
two--the Proterozoic and Phanerozoic--the world of dark and the world of
light.
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