Sequence complexity in Darwinian evolution

Whether or not Darwinian evolution leads to an increase in complexity depends crucially on what we mean by the term. Physical complexity is a measure based on automata theory and information theory that turns out to be a simple and intuitive measure of the amount of information that an organism stores, in its genome, about the environment in which it evolves. It can be shown that the physical complexity of the genomes of clonal organisms must increase in evolution, if they occupy a single niche and if the environment does not change. This law of increasing complexity is a consequence of natural selection only and can be violated in co-evolving systems as well as at high mutation rates, in sexual populations, and in time-dependent landscapes. Yet, co-evolution, because it can be viewed as creating an increase in physical complexity across niches, is likely the agent of a global increase in complexity. © 2003 Wiley Periodicals, Inc. Key Words: evolution; complexity; entropy; information; digital life T he controversial nature of discussions about a trend inthe evolution of complexity can be traced back to a lackof agreement on the definition of complexity. For some, it is obvious that complexity has increased, whereas others claim that there is not enough evidence to argue for or against an increase, and others still deny that “progress characterizes the history of life as a whole, or even repre