Monday, September 12, 2005

The accident of human evolution

Dr. K.Rohiniprasad

We humans would like to imagine that the gods created us to lord over the earth. It certainly appears to be so because no one has ever come across a monkey that undertook space-walk or a tortoise that designed a nuclear reactor. We have left all the fellow-creatures of this planet far, far behind. The advantages we enjoy are obvious. Human beings, with their complex brains, epitomise neural complexity and consciousness. That is what sets us apart. We have perception, fore-thought and social life that gives us tremendous advantages in terms of collective knowledge and wisdom. We comprehend, control and sometimes defy nature. We have understood the creation of life and achieved longevity, if not immortality. Our brains have become more complex and competent with time.

But how did this complexity come about? Why were the other animals denied this privilege? Popular perception is that life began in its simplest form and went on getting more and more complex until ‘finally’ humans evolved. Things have not been that simple. Humans probably represent the pinnacle of neural complexity. There are several other ways of defining evolutionary success. Bacteria, for example, have grown in numbers that can never be surpassed by other life-forms. To return to humans, how did the ‘blind’ forces of evolution achieve such ‘progress’? There were several steps that began with the beginnings of life itself. And the most surprising thing is that it was the culmination of a long series of several unrelated and random events.

Evolution is a fact, not theory. One has merely to look at various life-forms to understand how all of them share fundamental characteristics. Charles Darwin suggested natural selection as a struggle among organisms for reproductive success. While the basic theory is still considered correct, more modern interpretations of the above theory explain successive adaptive changes at the genetic level. As is now well-known, the genetic makeup of parents undergoes random mutations or changes in the offspring. Some of these changes are expressed as physical characteristics that may or may not suit the environment. Genetic diversity brought about by these changes help the species to evolve by competing for survival as the environment changes.
Although evolutionary changes occur very slowly, some of these adaptations can be observed during our life spans. Gypsy moths in England had to adapt themselves to a quick change in the environment during the industrial revolution. As coal and other massive amounts of air pollutants vitiated the atmosphere, light-coloured tree trunks turned dark. The original colour of the gypsy moths sitting on these trees was light grey that provided camouflage against predators. With the change in the environment this no longer worked and the moths became easy prey. The dark grey moths which were once quickly eaten by predators, now survived and bred, while their lighter counterparts were dying. As a result of man-made causes, the gypsy moth gradually adapted its colouring to match the surface of the darkened trees. Natural Selection ensured that only the dark-coloured moths survived.

Carl Sagan cited another example of human intervention in the case of the survival of the Heike crabs in Japan that bear the likeness of a samurai warrior’s face. A 12th century emperor thought samurai warriors were reincarnated as crabs but there is a much simpler explanation. Random mutations result in various types of crabs. For thousands of years superstitious fishermen considered it bad luck to consume a crab that bears a human face and kept throwing them back into the water to avoid angering supernatural forces. The more the shell looked like a human face the more likely it was for the crab to survive. Very soon the area proliferated with samurai crabs while the ones that did not have the pattern, were eaten.
We should also take into account mass extinctions of species for reasons that were unrelated to adaptive struggles among species. While all changes were brought about by external conditions, these were sudden physical or environmental changes. An important example is the sudden disappearance of dinosaurs about 65 million years ago after 150 million years of domination. It was probably due to the impact of a giant meteorite. There are several other evolutionary ‘jumps’ in the history of the earth.

While the earth is 4.6 billion years old, the oldest rocks formed out of its molten surface about 3.9 billion years ago. Life on earth first appeared about 3.5 billion years ago, and for billions of years it consisted of simple, single-celled organisms such as blue-green algae and plankton. All that changed about 535 million years ago during a period that can be called as biology’s big bang. This process ended within 10 million years, about 525 million years ago. These steps were discontinuous and episodic and definitely not gradually accumulative. The physical and geological factors that could have caused these sudden changes are being studied by modern scientists. What is important is the randomness and ‘lack of design’ in the process of evolution, which seems to be propelled by external conditions.

What about us? As the evolutionary biologist Stephen Jay Gould puts it, humans arose as a fortuitous and contingent outcome of thousands of linked events. We should humbly acknowledge the fact that any one of these events could have occurred differently and sent history on an alternative pathway. We have to remember that earth’s atmosphere in the early days did not contain enough oxygen to sustain animal life-forms. It was the growth of plants that absorbed the abundant carbon dioxide in the air and released copious amounts of oxygen. The energy released by photosynthesis is insufficient to power locomotion. That is why compared to plants and trees, oxygen-inhaling animals possess greater energy.

Humans evolved from just one branch of animals which include more than one million living species, grouped into approximately 35 phyla. Each phylum is a major category of organisms with a common design or organization. The characteristics are shared by all members of the phylum with some structural details brought about by evolution. All members of a phylum have a common ancestry. In this classification, sponges, molluscs, flat worms and vertebrates belong to different phyla. Humans are vertebrates, which belong to the phylum of Chordates. Birds, fish, frogs, reptiles and other mammals also belong to this phylum. We should remember that this branch comprises only one or two percent of the living species. Nor is this the greatest. Phylum Arthropods that includes terrestrial animals like spiders, crabs and other insects, is more successful in sheer numbers, total mass, and distribution than all other groups of animals combined. The remaining animal phyla are composed of mostly marine-dwelling organisms.
Gould cites four important twists in the ‘tale’ of human evolution. They show that there has been no ‘pre-determined’ path to human evolution. Nor is there any evidence of destiny or design. These events were quite mundane and have been described in several scientific articles.

The first event took place during the biological big bang. Among the many 525 million year old multi-cellular creatures that suddenly burst upon the earth, only one turned out to be the fore-runner of vertebrates. The others were mostly molluscs. The hard-to-recognise ancestor of ours had flexible, rod-like primitive backbone from which the spinal column developed.

The second major step towards the evolution of humans occurred between 408 million and 360 million years ago when some of these vertebrates became terrestrial. A small, insignificant group of fish evolved fin bones capable of bearing weight on land. These were animals with backbones that evolved from air-breathing freshwater fish. This probably happened during the time water ponds were getting smaller and far-between. After their successful invasion of land, amphibians diversified into many forms that included mammals and humans.

The third major occurrence was the impact of a meteorite. This cataclysmic event apparently drove dinosaurs to extinction and allowed mammals to dominate. Until then, dinosaurs had grown in numbers and variety and roamed the earth during the day. Mammals were furtive little nocturnal creatures that could not come out during the daytime. The sudden disappearance of dinosaurs and climatic changes helped mammals to proliferate into many forms. Primates were just one branch that adapted itself into some kinds of environment.

Subsequently, 2 to 4 million years ago the fourth major event took place when a small lineage of primates evolved an upright posture on drying African savannas. But for this, we would have remained apes that would have become ecologically marginal, in spite of some complexity in behaviour. While the other apes remained confined to arboreal existence, environmental changes drove early men into migratory travels that exposed them to a variety of living conditions. This brought about unprecedented growth in their experience and intelligence.
It is important to realize that the above four incidents were totally unrelated and random. Like every other phenomenon or catastrophe that changed the course of events on the earth, biological evolution trundled along without any pre-ordained plan or purpose. It is impossible to cover these facts for the Creationists.


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