For a long time, people looked at this perfection13 and thought: "This can only have been constructed by an all-knowing and all-powerful god." This is a theory. And it has not yet been falsified. But is it also a good theory?
If you remember, a good theory should meet at least two conditions: It should be of help in explaining matters and it should not produce conflicts with the rest of the knowledge. Some theories even should be usable practically.
The theory of god as creator is not the kind of theory that we should be able to use practically. It is a theory that makes it possible to explain the perfection and origin of nature. And that, it really does. It is an easy explanation and an answer to many difficult questions. But does it also meet the second condition? In the old times when you did not go to the doctor but to the medicine man and he helped you by talking to the spirits, it really was a good theory, because the life and knowledge of the people at that time was full of ghosts, witches and other supernatural powers. It was a natural thing to believe in god or even in many different gods. But as the scientific knowledge increased and more and more things that could before only be explained by supernatural powers were found a scientific explanation for, it got increasingly difficult to believe in such a power. The other explanations were better theories, because they could be used practically whereas it was very dangerous to rely on supernatural powers.
Of course the existence and influence of supernatural powers could never be falsified because one could always argue that they were not in the mood for helping when they did not. But nevertheless, the scientific explanations were better, because they were reliable. So with the scientific revolution the supernatural powers were taken away more and more of their influence and power on people's lives. And at some point, it got so difficult to believe in these ruling classes for the people whose knowledge now consisted mainly of scientific explanations, that they tried to find another explanation even for the wonder of creation.
Charles Darwin14 was the first to find such an explanation15. And this explanation is really a wonderful theory for those humans whose knowledge is made of scientific and natural explanations. Why is it "wonderful"? Because it not only meets all three conditions for a good theory16, but it is also nearly as easy as the explanation with the supernatural creator. This theory is the theory of evolution.
On the basis of many different zoological facts, Darwin showed that the emergence of creatures is a historical process of evolution. But his most important achievement was, that he found a great causal explanation for this evolution. His explanation rests upon two main principles: 1. hereditary variation and 2. selection of the better adapted. Animals normally produce more offspring than would be necessary for the survival of the species. As life is dangerous for example because of predators and difficult because there is competition for food, water, space and partners, the individuals that are better adapted to solving these problems have a higher probability to survive and produce offspring (selection). The offspring is always a little different to its parents (variation), but it nevertheless inherits most of their attributes. So it is very probable that the parents pass their good qualities on to their offspring. Like that, good properties (for survival and reproduction) spread easier in the population than bad ones, because individuals with good attributes produce more offspring which tend to have the same good attributes.
Darwin did not know anything about genes and he did not know how the variation might work. Now, we have a lot of detailed knowledge about that. We differentiate between two main types of variation: 1. mutation and 2. recombination. Put very simply, mutation makes random variations to the genetic code17. For example, a letter of a "word" of the genetic text could be deleted or a random new one inserted at a random position. This changes the structure described by the gene. If the gene is activated, the cell will therefore produce another protein18. And this might change the power that this cell has in cooperating with the other cells and it might change an attribute of the whole individual. While mutation can happen all the time, recombination is only possible if two individuals get together and do something that combines their genomes. In the case of higher animals this is called to have sex19. Recombination can cause huge variations, but it does not create any new genes like mutation20. It simply takes the code of the mother and that of the father and produces a mix of the genes of both. The most prominent type of recombination is called crossover. Somehow21 crossover manages to produce a mix that preserves all important attributes. The great majority of children have all the genes that are necessary for their complex development to a fully grown creature that looks and functions nearly like its parents.
Also bacteria have sex. But their recombination is of a quite different type which is made possible by a process called conjugation. Two bacteria build up a hose-shaped connection through which one of them gives a piece of its genome to the other. This sounds a bit as if it was the same thing as when we produce offspring. But it is not. The difference is, that in our case the two genomes exchange parts of their information, whereas in conjugation one is the donor and the other the recipient22.
As we have seen, recombination provides new combinations of attributes and mutation creates new attributes. In combination with selection, which favours attributes that are good for survival and reproduction, the average genome in the population of creatures gets better and better in solving the problems of life. As one problem of life is the competition between the different individuals for resources, it is good for an individual to adapt to a new environmental niche. In the course of 3,750,000,000 years, this led from the simplest known organisms to the many different perfectly adapted species that now live on earth23.