Extinction: Evolution and the End of Man. Michael Boulter
are frightening, yet the protection of knowing they are virtual images is comforting – like Little Red Riding Hood’s wolf, they aren’t around any more. They are no longer a direct physical threat but remain as frightening images in our minds.
Imagine the scenery while striding along the quayside at Lyme Regis in Dorset, the location of The French Lieutenant’s Woman and countless television films about eighteenth-century swashbuckling. Centuries ago, the curve of the quay was built of large blocks of local rock which still protect the small harbour from the weather of the English Channel. The stones show remnants of earlier life embedded in the rock, fossil mussels and oysters from the Early Jurassic sea that flowed along this coast 200 million years ago. We walk down the quaint old steps, slipping on familiar slimy green seaweeds, ancient algae which also grew in the Jurassic sea. Down at the bottom of the steps the water laps as it has almost always done. We climb into our small rowing boat and the oarsman unties the ropes to cast off. Out of the small harbour and into the bay we float to a world apart: miles of ocean, a warm wind. The boat rocks with the waves and transports us to the edge of fantasy. We are off to see the dinosaurs.
Two hundred million years ago the sea there was much warmer than today, with very little wind and only small waves. Visitors like us would find breathing difficult with less oxygen in the atmosphere, and with the high humidity we would feel distinctly uncomfortable. We cool off many times by swimming from the boat in water much less salty than what we are used to. One of our group swims into a large submerged object shaped like a circular buoy, which then squirts sea water all over us in the boat as we row off quickly, scared by the turbulence. It is an ammonite.
These predecessors of the modern nautilus have a flat spiral body protected by a tough round shell. They move sluggishly through the waves, just a little faster than us. Some of them are about the same size and just as seaworthy as our boat. Their large buoyancy chambers under the carapace suck and blow air like a jet engine, and their mouths flush out fish and plankton with clumsy movements. From evidence in their fossil graves we think that many of the smaller species did not dare leave the shore, fearful of being chased by larger predators. They basked in the strong sunshine waiting until the high tide for their next meal. Many of the fish in the same sea have long sharp snouts specially designed for fighting, while in the air there are the flying monsters, which we can see from our exposed position on the rowing boat.
A flock of more than twenty skin-winged pterosaurs swoop down to attack, their spearlike teeth ripping into the surface-feeding fish that we have attracted around our boat. The sea turns dark as the energy of these beasts churns up the water to rock our boat. But they are as scared of us as we are of them, and they fly off with their prey as fast as they arrived, leaving behind a trail of debris. That draws new attention to our terrifying position, this time from feathered foe: scavenging birds and Archaeopteryx. Their visit is as timid as the ammonites’. These early ancestors of the birds have left evidence in the rocks that they swallowed the remnants whole and then regurgitated the indigestible remains, as owls do today.
There is also evidence of the food chain to show that the ammonites ate the plankton, that fish ate the ammonites, and that dinosaurs ate the ammonites and the fish as well. Through the earlier Triassic Period, sharp-toothed dinosaurs called nothosaurs, 4m long with small heads, long necks and tails, swam with small paddle-like limbs and ate the fish. We know that fish ate ammonites because their teeth marks have been found on ammonite shell tests. Sometimes the food chain was extensive and new or different species got involved, arthropods for example (invertebrates with segmented bodies, like lobsters). Broken bits of their bodies have been found in the fossilised dung and stomachs of marine reptiles as well as the regurgitated pellets from birds of prey. In their turn, the arthropods may have fed on small ammonite species, which then lived on the plankton ooze.
The food chain is part of the system, all changing slowly in tune with the environment. Together they form part of a gentle rhythm. If one part changes, the rest is affected. Nowadays, very similar rhythms are generated when crowds of people create an atmosphere of bustle of the kind you sense in airports and hotel lobbies. Out of the season there is a constant stream of people walking in different directions, positive with a sense of purpose, living and working with quiet efficiency. However, around Christmas and the high summer holidays they are different places, overcrowded beyond what the system was designed to carry, with people jammed, waiting, arguing in frustration.
The pace of life on the planet also changes through time. Ice ages and periods of high volcanicity are the equivalents of the busy, rushed days before Christmas at Heathrow. Conversely, the Jurassic and Cretaceous were off-peak times, with only one or two spurts of intense activity. Throughout this time biological evolution continued at a slow and steady pace in response to the equally modest environmental changes. Just as in airports and hotel lobbies outside rush hours, there were a few new journeys started, a few new species registering, but no major upsets. The relatively stable environment, the ecological balance and the steady growth in diversity saw evolution work mainly at the species and genus level. It was a bustling rhythm but without major divergences or catastrophes.
Back in our Jurassic boat we approach the shore, where we can see species of the two dinosaur groups. The Saurischia, with hips like lizards, stand on two legs to fight other animals in the famous Tyranno-saurus pose. Those with the heavier bodies and smaller heads, the Ornithischia, browse on the tough leaves of cycads and conifers, and walk around passively on four legs. This other group, with hips like birds, were vegetarians. They were also heavily armoured against attack from early Saurischia like Tyrannosaurus.
We know so little about their inter-relationships that the view from the rowing boat remains a fairy story. A popular view is that all this lighting, all this competition between individuals and species, is the motor of evolution. That is a myth from Victoriana, placed under the Darwinian banner of ‘survival of the fittest’. It’s an old-fashioned concept that should be banished to the annals of what is wrong about biology. Now, we know that the complex relationship between the organisms and the environment is also important. Evolution is less to do with winning battles between species and individuals, more to do with being able to live well together in the same environment. It is not necessarily the strongest that succeeds, but the most adaptable to new environments that might develop suddenly and unexpectedly.
In the tranquil times of the Jurassic and Cretaceous there were very few and undramatic environmental changes. Temperature and CO2 concentrations steadily increased well above today’s values. The vicious battles between individuals and groups of Mesozoic monsters did not encourage major evolutionary changes. New species took over from earlier ones, a few new Families originated when there was a major altercation in battle with other animals or with any of the rare environmental changes. A few species and even genera became extinct. There was peace and relative quietness on Earth: evolution happened on a small scale, origins mainly at the species level, a few genera and fewer Families. Without big environmental changes there are few, if any, big evolutionary advances. Especially during the middle of the Jurassic there were only small and subtle changes in the marine and terrestrial environments. Without catastrophe there were only small evolutionary changes during the time, usually at the level of the species and genus.
Of the many important things to be learnt from these most tranquil of ages, there is one that most people do not expect. A popular view is that all the fighting, all the business of one thing eating up another, is the primary drive of evolution. They say it leads to the evolution of man and our seeing ourselves as the most powerful beings, sitting at the top of the evolutionary tree. This is not how nature works. The ammonites that ate most fish or resisted attacks from a soaring Pteranodon’s beak didn’t necessarily do any better than the more compromising species. So the bravest ammonites, charging off to battle in the front lines, perished in larger numbers than the more modest cowards who had found a safe niche.
What did survive were those most able to succeed when the environment changed. So the creatures that come to dominate at any given moment do so, not by power of fighting but by chance. They have just happened to fit into new surroundings at that particular time better than the others. As the environment, or internal biology, or social behaviour, changed, so they just happened to be in the right place at the right time with the right kind of biology. Now, humans