Man After Man: An Anthropology of the Future, page 2
With the increasing complexity, the different cells in a single creature evolved to have different functions. Some cells were involved in sense, helping the creature to find food or light. Other cells were involved in locomotion, in moving the whole creature towards its food or its light source. Others were involved in digestion, others in reproduction, and so on.
The different masses of cells are what we call tissues, and the structures that they form, each with a different function, are called organs. An entire creature (made up from molecules that make cells, that make tissues, that make organs) is called an organism.
At an early stage the pathways of evolution began to branch, and different types of organism developed. Wherever there was a food source that could be exploited, evolution produced an organism able to exploit it. Such a process is called adaptive radiation, and we can see it at work today.
Many species of finch live in the Galapagos Islands, off the west coast of South America. These all evolved from one type of seed-eating ground finch that came over from the mainland, and spread to all the islands, each with different habitats and food sources. The finches on each island evolved to take advantage of their particular habitat. As a result there are now many species of finch on the islands, including heavy-beaked forms that eat seeds, short-beaked forms that eat buds and fruit and longbeaked forms that eat insects.
Environments are not stable; they change for one reason or another. When this happens, a creature evolved to live in a particular way in a certain environment becomes extinct. For example, if all the insects on the Galapagos Islands died out, then the long-beaked finches would become extinct: a process known as natural selection. If the insects became extinct, their places would be taken by another creature, and some other bird would evolve to eat that.
Evolution produces specific shapes of animals to live in particular environments. Grass is tough to eat, so an animal that eats grass needs strong teeth and a specialized digestive system. Grasslands are wide open areas in which danger can be seen coming from a long way away, and there are no hiding places. A grass-eating animal, therefore, tends to have long running legs, as well as strong teeth, and a long face so that its eyes are above the level of the grass while its head is down eating. This gives us the shape of the antelope – the typical grass-eating animal of Africa.
However, the grasslands of Australia have evolved a quite unrelated grass-eating animal – the kangaroo. There seems little resemblance between this and the antelope of Africa. It does, however, have the same long face with similar grass-grinding teeth; and the legs are long and built for speed, albeit in a bounding rather than a running gait. This development of similar features in unrelated animals in response to similar environmental conditions is what is known as convergent evolution. It accounts for the similarities between seals and sealions, aardvarks and anteaters, ants and termites, vultures and condors.
A similar phenomenon is parallel evolution. In this, two branches of the same family tree develop along similar lines independently of one another. For example, the kit fox of North America and the fennec fox of Africa are both small, with a sandy pelt and large ears. The ears act as cooling vanes and prevent each animal overheating in its desert environment, and the pelt is camouflage. Both are descended from a more conventional fox-like animal, but each has evolved separately to live in different deserts.
The different colours and patterns in animals can also be attributed to evolutionary processes. Animal patterns may camouflage them: on the other hand they may, like the skunk, have striking colours that warn a would-be attacker that the owner is poisonous. Some animals mimic others, as when a harmless king snake develops the spectacular pattern of the poisonous coral snake, and consequently turns away potential enemies. All these have developed because the animals concerned have benefited from them, have survived and have gone on to reproduce.
Throughout the world and throughout time, animals and plants have changed in response to the changes in the environment.
One species has broken with this tradition. Within the last million years or so the human species Homo sapiens evolved. It has come all the way from molecules to its present form in 3500 million years by the workings of evolution. Now, within the last few millennia, intelligence has developed, and with it cultures and civilizations. The species has spread not by changing to adapt to the environments it found but by changing the environments to suit itself. Instead of developing furry pelts and layers of insulating fat to adapt to cold conditions, it manufactures artificial coverings and uses available energy supplies to generate heat for the body. Instead of evolving heat radiating structures such as big ears to adapt to hot conditions, it manufactures refrigeration and air-conditioning systems, again using available energy supplies. Instead of developing speed and killing strategies that allow it to hunt a particular food, it builds machines to do it. By using its intelligence it can exploit all food supplies in all environments without having to change itself.
Medical science eliminates much of the effects of natural selection: no longer does an individual not particularly well adapted to the environment die out before being able to reproduce.
Under natural conditions not all offspring of a species survive, and this is reflected in the birth-rate. Thanks to medical science, more offspring of Homo sapiens survive than ever could before, but this has not been reflected in a corresponding drop in the birth-rate. As a result the populations of Homo sapiens are growing without the refining and modifying processes of natural selection.
Evolution as we know it for Homo sapiens has stopped. However, this does not mean that the process of change has necessarily stopped.
As science develops, the reproductive molecules – the genes – that exist within every cell of the human body are becoming better and better understood. When Homo sapiens finally appreciates which parts control the development of which features, then the possibility exists for modifying the process. A stage will be reached when one gene can be suppressed, another encouraged, with yet another created from new. A human being with particular features, following a particular preconceived plan, may be born from modified sperm cells and ova. Without the natural processes of modification, this unnatural process is the only way of developing the species into new forms to face the problems that await it in the future: problems generated by overpopulation, over-use of natural resources and pollution.
The mechanics of genetic engineering are already complex, yet in their current state they are primitive compared to what will undoubtedly be possible within a few decades.
The reproductive molecules that lie at the nucleus of each cell of a living organism are in the form of long structures called chromosomes. These chromosomes are made up of the chemical substance DNA. Its shape is best imagined as a long ladder that has been twisted along its length. Each rung of this ladder consists of two compounds, called bases, locked together. There are only four different kinds of bases: thymine, cytosine, adenine and guanine, referred to as T, C, A and G. A T always unites with an A, and a C always with a G. The sequence of these base pairs along the twisted ladder of the chromosome is almost infinitely variable – there are something like 6,000,000,000 bases in a full set of human chromosomes.
A chromosome is often described as a page in an instruction manual. Each base pair, or rung in the ladder, represents a letter of the alphabet, and the arrangement along the ladder gives ‘words’ and ‘sentences’. Each understandable instruction so formed gives a gene. The genes in a single cell produce the total information needed for the growth of the entire organism.
When an organism grows and develops, it does so by multiplication of cells. Each cell splits into two complete cells. When this happens, each chromosome in the cell actually splits down the middle. The uprights of the twisted ladder pull away from one another as the rungs split into two along the joins between the bases. What happens then is that these two half-ladders build up two complete ladders by attracting
The exception to this process is in sexual reproduction. Reproductive cells carry half the normal number of chromosomes. Two half-cells unite during fertilization to produce one cell with the full number. This new cell is a unique mix of genes, half from the mother and half from the father. This cell then divides in the usual manner until the entire organism is built up, following the instructions now carried in every cell.
The big mystery now is this: how do the genes – the pattern of base pairs along a chromosome – actually work? How do they control the construction of an organism?
The idea behind genetic engineering is to manipulate natural processes. In some way genetic instructions along the chromosomes in a cell have to be identified then changed so that as the organism grows, it is to a new set of instructions. Since all the materials involved (cells, chromosomes, molecules) are microscopic, a whole new technology has to be applied.
Viruses can do it. Viruses essentially consist of a mass of their own DNA encased in an envelope. When they infect a cell they attach themselves to the cell’s wall and inject their DNA through it. In the cell’s interior the invading DNA breaks down the cell’s chromosomes and rebuilds the material into copies of itself.
For genetic engineers to do the same, they would first of all have to break in through the cell wall, then break down the DNA of the nucleus and reassemble it in the desired way. Alternatively, they could cut out segments of the DNA strand, segments that correspond to particular genes, and replace them with DNA segments already prepared. This would be done by chemicals that have specific biochemical reactions – enzymes – some of which have been found to have the ability to cut DNA strands.
The greatest experimental successes so far have been with bacteria. These single-celled creatures have cell walls that can be softened by chemical solutions so that new DNA can be placed inside. The double helix of the original chromosome can be chopped up using enzymes, and new DNA can be inserted. The broken ends of the DNA strands have one side longer than the other, exposing a sequence of bases. If the introduced DNA segment has matching bases exposed at its end the two DNA pieces will unite, T to A, and C to G, and produce a complete chromosome. This technique is known as gene-splicing.
Before any of this can be attempted, however, the whole gene pattern has to be mapped. At the moment only about 100 human genes have been identified and interpreted; but, since genetics has only been in existence for a century, and the structure of the chromosome has only been known for about four decades, and scientific advance in this area is increasing exponentially, what was speculation about genetic engineering is quickly becoming fact.
1. A human being is made of cells – about 10 trillion of them – all grown from a single reproductive cell.
2. Each cell contains a nucleus, carrying all the genetic information for growing the whole body,
3. The genetic information in the nucleus is arranged on a number of units called chromosomes.
4. Each chromosome is made up of a long strand of DNA coiled upon itself again and again,
5. A DNA strand is a twisted ladder of pairs of amino acid molecules, the sequence of which provides the genetic information,
6. When a cell reproduces, each DNA strand splits like a zip fastener along the joins between the amino acid molecules, Each half then builds up a complete strand by attracting to itself the free amino acid molecules drifting in the fluid of the cell.
Genetic engineering of human beings would consist of removing a reproductive cell from a human, altering a known gene in some predetermined way, and replacing the cell so that it grows to a full-term foetus with the desired characteristics.
1. The cell is removed.
2. The gene to be altered is identified on the chromosome.
3. It is replaced with a predetermined gene.
4. The cell is replaced in the womb.
5. An altered human being is born.
PART ONE: IN THE BEGINNING – The Human Story So Far
8 MILLION YEARS AGO
Ramapithecus – ancestor of apes and humans.
Her ancestors lived in the treetops that once covered the area. Indeed her relatives still live in the forests of the steamy lowlands, climbing the branches, eating the soft fruits and grubs; her way of life is, however, completely different. Hers is a dry landscape of yellow grass, with brown and black thickets of hardy thorn trees.
Her woodland diet is different, too, because there are no soft fruits and juicy buds or grubs here. Solid nuts and tough seeds are her main foodstuffs, and when there is nothing else she makes do with coarse roots and tubers. Hard-shelled insects and dry lizards abound, and she often extracts what little nutrition there is from these. Her jaws and teeth reflect the fact that she has to eat more than her ancestors did to gain the same amount of goodness, and she has to chew it more thoroughly. Accordingly, her front teeth have become smaller to make room for broad and flat back teeth that grind down masses of coarse food. This has not happened suddenly, but has developed over thousands and thousands of years. Those who study her remains will give her a name. They will call her Ramapithecus.
The other animals that live here show the same specializations in their teeth. Pigs and antelope feed on low-lying plants, and giraffes browse the higher trees. These too have broad back teeth; but she has a long way to go before she is as well-adapted as they are.
For one thing, the grasses are very tall, and when she is on the ground she is lost and cannot peer over them. There are fierce hunting beasts around, too, so she needs to climb the trees for safety as well as to see distances. The other animals run away when threatened, but she does not have the speed, running on all fours on short limbs.
Stiffly she pushes herself to her hind feet, and sways unsteadily for a time. Now she can see over the top of the grass, and, what’s more, she feels cooler. Less of her back is exposed to the hot sun, and the cool breeze that she now feels soothes her neck and chest (overheating was not a problem in forest shade). The more comfortable temperature, however, is counteracted by discomfort in her legs, as this is not a natural pose for her. Maybe she can move more quickly like this, with only two feet touching the ground. She tries but her legs are not strong enough, and are the wrong shape for this to work. Her body naturally topples forwards, and she cannot move her hind legs quickly enough to stay upright.
She descends once more onto all fours. No. She will have to stay near the trees if she wants to survive.
3 MILLION YEARS AGO
The climate is much drier now, and the scenery has changed considerably. The continent has been moving, gradually splitting the landscape across with faults, while elongated slabs have slowly subsided forming long, deep, rift valleys with strings of shallow lakes in their floors. Molten material has been brought up from the Earth’s interior, and active volcanoes line the edges of the rift. Grasslands have spread everywhere and there are many clumps of trees, but no continuous forest.
At the edge of one such clump a small creature drops from a tree to the ground; and then stands upright. He looks around for danger and, seeing none, grunts a signal. The dozen others who drop from the branches and cluster around him include other males, much smaller females (some with babies) and children – it is a large family group.
Food has become sparse in their thicket, and they are moving. Further down the valley a patch of green by a lake holds out some hope. With a confident stride, they march downhill, leaving footprints in the volcanic ash that carpets the whole area from the last eruption. Their stride and their stance show that their legs have developed considerably in the last 5 million years. From permanently-bowed structures only good for climbing trees, their legs have developed into straight limbs that can carry their bodies vertically. Their arms, however, have changed little during that time: they still have the curved fingers for grasping branche
If the landscape becomes much drier, though, and the trees more sparse, beings that are better adapted for a ground-dwelling existence will be more likely to survive than this partially tree-living creature, Australopithecus afarensis.
That time is not far off.
2.5 MILLION YEARS AGO
Australopithecus robustus – the vegetarian dead-end.
Australopithecus africanus – the adaptable survivor.
Volcanoes still bubble; grassy plains still spread along the rift valleys, but now only isolated umbrella-shaped trees and low thorn thickets break up the yellow of the landscape. Down by the edge of the lake a pack of large hyenas has brought down an animal that looks like a short-necked giraffe with moose-like horns, and are tearing its corpse apart.
In one mass of bushes a number of heavy-looking beasts forage amongst the thorny vegetation for leaves and berries. If it were not for their upright stance they would be mistaken for chimpanzees, as they have the same heavy bodies and the same deep jaws with massive teeth. These also belong to a species of Australopithecus, called Australopithecus robustus, and they are perfectly at home here as they contentedly chew any piece of vegetable material they find.
Suddenly the nearby grass erupts. About a dozen screeching figures run at the feeders. They look much like the others, but are more lightly built and their faces do not have such a heavy-jawed look. They belong to another species, A. africanus.
The feeders stop eating and snarl back, staring defensively at the newcomers and showing their teeth and gums. They are not to be chased away from their feeding ground.