For example, creationists often explain the development of resistance to antibiotic agents in bacteria, or the changes wrought in domesticated animals by artificial selection, by presuming that God decided to create organisms in fixed groups, called "kinds" or .
Though natural microevolution or human-guided artificial selection can bring about different varieties within the originally created "dog-kind," or "cow-kind," or "bacteria-kind" (!
These digital offspring then go on to the next generation, forming a new pool of candidate solutions, and are subjected to a second round of fitness evaluation.
), no amount of time or genetic change can transform one "kind" into another.
However, exactly how the creationists determine what a "kind" is, or what mechanism prevents living things from evolving beyond its boundaries, is invariably never explained.
These promising candidates are kept and allowed to reproduce.
Multiple copies are made of them, but the copies are not perfect; random changes are introduced during the copying process.
The evolutionary postulate of common descent has aided the development of new medical drugs and techniques by giving researchers a good idea of which organisms they should experiment on to obtain results that are most likely to be relevant to humans.
Finally, the principle of selective breeding has been used to great effect by humans to create customized organisms unlike anything found in nature for their own benefit.
These candidates may be solutions already known to work, with the aim of the GA being to improve them, but more often they are generated at random.
The GA then evaluates each candidate according to the fitness function.
Again these winning individuals are selected and copied over into the next generation with random changes, and the process repeats.
The expectation is that the average fitness of the population will increase each round, and so by repeating this process for hundreds or thousands of rounds, very good solutions to the problem can be discovered.
The shape of a protein determines its function.) Genetic algorithms for training neural networks often use this method of encoding also.