it has been known that some at least of the basic molecular building blocks of life – the amino acids – can be produced by subjecting mixtures of these gases to the levels of ultraviolet radiation and the types of electrical discharge that would have been around in those early days. Simple chemical processes would have enriched the prehistoric broth to the point where it contained several of the necessary chemical ingredients of life.4
It is a long way, though, from simple proteins and sugars to the molecules and structures that are characteristic of all living systems, from amoebas to Buddhas. There are 200 or so of these essential ‘molecules of life’, and they collaborate with each other in such intricate and self-supporting ways that the whole structure of relationships on which life depends seems to hang together like a multidimensional archway – remove one piece and the whole thing collapses. And while some of them can be found in different brands of primordial soup, many of them, in order to be synthesized, seem to need exactly the kind of environment provided by the living cellwhose origins we are eventually trying to account for. We are faced with a classic ‘Chicken and Egg’ situation: in order to explain how cells were made, we seem to need to postulate the existence of cells!
There are a number of ingenious theories about how the bridge between simple molecules, and life, was built. Graham Cairns-Smith of the University of Glasgow has suggested that, just as an archway needs a temporary support while it is under construction, which can then be taken away when the arch is finished, so the first molecules of life were able to be synthesized and concentrated within the tiny cell-like cavities that are present in certain types of clay. Once these carbon-based molecules had formed their mutually supportive society, they were then able to kiss the clay goodbye.5 However it happened, there emerged, amongst these molecules of life, the ones that were to serve as the powerhouse for the whole of evolution: the self-replicating molecule known as DNA. Each DNA molecule is like a long message, an instruction manual for making all the different constituents of living matter, written in an alphabet comprising only four letters. A simple bacterium needs a manual equivalent to about 1000 book pages to make it and keep it going. The ‘library’ needed to construct and run a human being, contained within the 46 chromosomes of every cell in the body, is equivalent to about a million pages. And, of course, each of these chromosomes is able to photocopy itself with incredible accuracy and elegance, whenever its parent cell divides.
Under the conditions that might have been expected 3,500 million years ago, amino acids have been shown to form into primitive celllike structures. By 3,000 million years ago, cells had developed which were able to generate energy from light: they were capable of photosynthesis. As this process consumes carbon dioxide, and liberates oxygen gas, the composition of the atmosphere was slowly but radically changed. The development of the ozone layer meant further reductions in the amount of ultraviolet radiation penetrating through to the Earth’s surface, and increasingly hard times for the original bacterial or prokaryotic cells. In order to take advantage of the changing conditions, much more complex kinds of cells developedthe eukaryotic cells, from which all multicellular species are derived. These basic building blocks of animal tissue are themselves comprised of collections of different kinds of simpler prokaryotes.6 Each of our human cells, for example, contains mitochondria, which were originally completely independent little creatures. They still have their own DNA which is quite different from that contained within the nucleus of their adopted parent cells, yet have chosen to settle down and work as the energy factories of the cell in return for board, lodging and protection.
The first multi-cellular organisms began to appear on the Earth about 700 million years ago. The basic design of the animal body has over millions of years ramified into the galaxy of different species of which television nature programmes constantly remind us. But the fundamental specification has remained surprisingly constant. Just as city society has evolved in strikingly similar ways all over the world, so the body has come to delegate its necessary functions to a familiar repertoire of subsystems. Like a colony of ants, but more compact and sticky, cells cling together, throwing their lot in with each other, and contributing their specialized talents to the overall good of society, in the hope that ‘All for One and One for All’ will turn out to be a successful strategy.
For example, all bodies develop subsystems whose job it is to turn food into a usable form, transport it round the far-flung part of the empire, and deal with waste disposal. Some citizens roll themselves into a tube, the walls of which learn to weep lubricants that soften the food and start the process of converting raw antelope or sunflower seeds into a usable nutritious juice. To make use of a greater variety of raw materials, some of them quite tough, other brave citizens build themselves into hard white rocks at the entrance to the tunnel, and crush the ore that passes between them. Constant supplies of fresh water are needed by the food processors, and the development of a flappy pink proboscis helps to flip moisture into the front end of the tunnel. While at the other end, sewage operatives divide the waste products into liquids and solids, and develop short-term holding capacities, so that the garbage can be dumped when it is safe, and smart, to do so. If you are evolving into a fish, it does not matter too much if you leak as you go; but if you are on your way to becoming a bird, you are at an evolutionary advantage if you can learn the trick of not fouling the nest.
To work properly cells, like cars, need not only suitable liquid fuel but air, so another subsystem evolves to extract the vital ingredients of air and deliver them. The body grows an internal complex of beaches, a vast coastline along which the air can continually lap, and where chemicals can trap the precious oxygen. In order to maximize the vigour and intimacy of this contact, the enfolded coastline develops into an internally-regulated bellows that constantly exchanges used air with fresh. While inside the body there develops an intricate network of canals that make Venice look like the Sahara desert, again with a central pumping station that keeps the currents flowing, and ensures that supplies reach every nook and cranny.
Ingestion is a crude process, and sometimes things get sucked in at the front end of the tube that interfere with or threaten the smooth workings of the community. Gradually some residents are delegated to lookout duty, their task to discover, through evolutionary trial and error, how to predict by sight or smell or taste what is wholesome and what it is better to avoid or spit out. But mistakes are still made, and so other members of the commune are bred for fighting, forming a territorial army that constantly patrols the system, riding shotgun on the precious supplies, detecting and overpowering intruders and dissidents before they can throw a spanner in the works. And this immune system has to develop the ability to tell, with great accuracy, friend from foe, so that it does not inadvertently submit innocent but unrecognized members of its own family to ‘friendly fire’. Chilean neuroscientist Francisco Varela has shown that these internal defenders of the community must possess, like the Freemasons, an increasingly sophisticated repertoire of secret handshakes which will unmask the imposters – increasing because the ranks of the potential invaders are always changing, and their powers of penetration and impersonation are always growing.7
Unless the whole body is fortunate enough to find itself rooted in the Promised Land, where abundant supplies of milk and honey naturally and continually drift into the open end of its tube, it may well discover the advantages of arms and legs. With arms (and especially with hands on the ends of them) that are hooked up to your lookouts, you are able to reach out and grab passing morsels that would not otherwise have fallen into the top of your tube. (A long sticky tongue that you can aim and flick does the same trick.) Legs expand your hunting ground even further, as well as enabling you to take some evasive action when you find that you have unwittingly strayed into someone else’s. Both attack and escape are hit and miss affairs, of course, and it will have taken hundreds of generations, and many of its great uncles starved or eaten, to get to the point where any animal is as skilled as it is. And each species is of course never a finished product, but just one snap-shot of the continually unfolding evolutionary drama.
What is Evolution?
It will be obvious that I am assuming the general validity of an