de Lizana, Mercedes Bleda-Maza, Hannelore Brandt, Ilse C. Gebeshuber, Michael MacPherson, Tetsuya Matsuguchi, and Szabolcs Számadó. Does complexity always increase during major evolutionary transitions? . na, 2003.
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There is a long raging debate about the evolution of biological complexity. Despite the common sense observation that evolution produces more and more complex organisms, there is no accepted argument in favor of increasing complexity during biological evolution. In fact, many notable evolutionary biologists have explicitly warned against drawing such conclusion. For example, Maynard Smith and Szathmáry (1995) conclude that the increase of fitness cannot be equated with the increase of complexity, and not even the increase of fitness can be taken for granted during evolution. Others argue that the recognizable patterns can be explained by a ``random walk’’ which started from the simplest forms, thus complexity is expected to increase not because of some underlying trends but because of the boundary conditions of the process (Gould, 1996). On the other hand, Adami (2000) and his colleagues
were able to show, with the help of evolving artificial life, that physical complexity must always
increase in fixed environments for organisms whose fitness depends only on the sequence of their genome. The obvious shortcomings of this approach are that the environment is rarely fixed and that the fitnesses of organisms might depend on many factors other than their respective genomic sequences. Yet observing the increase of structural complexity of living creatures can make another line of argument in favor of increasing complexity. The major steps of this process sometimes called the ‘‘major transitions of evolution’’ (Maynard Smith and Szathmáry, 1995). Structural complexity increases during these transitions by definition, but what happens with physical complexity? Clearly the physical complexity of those parts of the genome that code for the structural changes should increase, but what happens with the other regions? Can we expect an increase of complexity or not? To study the question we developed a computer simulation of a generalized transition event. The properties of the transitions were taken from the book of Maynard Smith and Szathámry (1995).