Feedback -- The Evolutionary Accelerator
What do we mean when we say the rate of evolution has speeded up? The world of physics has not speeded up. As far as we know electrons spin around the nucleus of an atom at the same rate as they did 10 billion years ago. Nor have the biological processes that underlie evolution changed; they are probably still occurring at about the same rate as they did when life first emerged on Earth.
What has accelerated is the rate at which change has occurred: the rate at which new species have come into being, and the rate at which those species have evolved new characteristics. It is, to borrow a term from the philosopher Alfred North Whitehead, the rate at which novelty has entered the world. The word novelty is used here, not in its everyday sense of some unusual or curious circumstance, but in its literal sense of newness.
Why has the rate of appearance of novelty accelerated? The answer is fairly straightforward, and has to do with what systems call positive feedback. It occurs whenever the current state of affairs promotes future growth. An example of positive feedback with which we are all familiar is the growth of population. The more people there are, the more children are born. The more children that are born, the more parents there will be in the future, and the more children will be born, and so on. If there are no constraints, the population keeps growing faster and faster.
Another common example of the current state of affairs accelerating future growth is money invested at compound interest. A dollar invested at 10 per cent interest would be worth $1.1 after one year; $1.21 after two years; $2.59 after ten years; $117.39 after fifty years; $13,780.65 after a hundred years; and around $2,473, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000, 000 after a thousand years, which is several trillion times the weight of the earth in gold (try collecting your interest on that).
The growth curve of evolution may not have been as smooth or as mathematically precise as the growth of compound interest -- the current view is that it has progressed through a series of dramatic fits and starts -- but positive feedback has nevertheless been at work at every stage.
A Platform for Life
The first molecules were simple compounds composed of just a few atoms. As physical evolution progressed, these collected together into larger, more complex compounds. The more compounds that were created, the greater the possibilities for further combinations -- and the more rapidly new molecules appeared.
Through this process there emerged the highly complex /MACRO-molecules of RNA and DNA containing millions of atoms. These brought with them a new and most significant characteristic -- they could produce copies of themselves. Nature no longer had to build these /MACRO-molecules through the combination of smaller sub-units; instead each molecule served as a template upon which copies of itself could be built. And these copies served as templates for further copies. Nature had invented its own way of learning.
Remembering modifications from previous generations, living cells were able to learn those characteristics that enhanced their chances of survival. And the better they survived the faster their numbers grew. In just one billion years of biological evolution a far greater degree of novelty emerged upon this planet than had appeared over the previous ten billion years of stellar evolution.
The Leap of Sex
Many of the new characteristics that evolved served as platforms for further developments. A good example is the advent of sexual reproduction some 1.5 billion years ago. Until that time cells reproduced by simply splitting into two, each of the new sisters being exact clones of the original. The opportunities for beneficial variation were very small, and any that did occur were isolated to the descendants of that particular cell.
With sexual reproduction, however, two cells came together, shared their inherited genetic information and produced offspring that contained a combination of their genes. No longer did it take thousands of generations for just one genetic difference to arise. Differences now occurred in every generation, speeding the rate of ingression of novelty a thousandfold.
Multicellular organisms, the first of which appeared some 1,400 million years ago, were another great leap forward. Working together in a community, it became more efficient for individual cells to take on special functions. Some took on tasks such as digestion, some formed a protective skin, others helped the organism move about.
From then on evolution was not limited to the creation of new species of cells. The muscle cells in a fish are not very different from the muscle cells in you or me. What has evolved is the way the cells are organized. This can change more easily and faster than the biological structure of the cells themselves. The result was another speeding up of development. The awe-inspiring diversity of species that we see on Earth today evolved in just the last tenth of Earths history.
From Senses to Brains
As time went on, organs appeared that, in addition to processing energy and matter, could also process information. Some developed into senses capable of detecting changes in the environment, others became rudimentary nervous systems able to convey information from one part of the organism to another, and store it for later use. The well-being and survival of these creatures now depended not only on the genetic learning of their ancestors, but also on the learning accumulated during their own lifetimes. And again the rate of change accelerated.
Nervous systems are delicate structures, and the earliest ones, distributed throughout the organism, were very vulnerable. With the evolution of a spinal cord and skull, however, the nervous system was protected inside a case of bone. Once this step had been accomplished the development of the nervous system itself became the major focus of evolution.
We tend to see vertebrate evolution in terms of the more visible changes in outer form -- gills evolving into lungs, fins developing into arms and legs -- but the most significant changes were taking place on the inside. The nervous systems of early worms occupied less than one ten-thousandth of the organism. The brain-to-body ratio of stenonychosaurus, one of the most intelligent dinosaurs, was probably about twenty times greater, but still not that impressive. With the advent of mammals, however, the nervous system began to grow very rapidly. Within the last 50 million years -- less than one third of the dinosaurstotal reign, and only a hundredth of Earths history -- brain size has exploded. In human beings the brain now takes up one twentieth of the bodys weight.
As important as the increase in the relative size of the brain is the increase in its complexity. As the brain evolved its structures became more and more intricate. The cortex, the outer layer of nerve cells believed to be the seat of thinking and higher mental functions, became much thicker, and unfathomably complex. The brains of humans (and of whales and dolphins) are, with no exaggeration, the most complex structures in the known Universe -- many times more complex than the largest computers such brains have yet designed.
This explosive development of the brain, occurring in just a few hundred thousand years, is one of the most dramatic and rapid changes in the whole of biological evolution. And on it rests the whole future of evolution. For through the human brain have come new creative potentials, new arenas for growth and development, and another leap in the speed of evolution.