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. 2000 Apr 25;97(9):4463-8.
doi: 10.1073/pnas.97.9.4463.

Evolution of biological complexity

C Adami  1 , C Ofria, T C Collier
Affiliations

Evolution of biological complexity

C Adami et al. Proc Natl Acad Sci U S A. .

Abstract

To make a case for or against a trend in the evolution of complexity in biological evolution, complexity needs to be both rigorously defined and measurable. A recent information-theoretic (but intuitively evident) definition identifies genomic complexity with the amount of information a sequence stores about its environment. We investigate the evolution of genomic complexity in populations of digital organisms and monitor in detail the evolutionary transitions that increase complexity. We show that, because natural selection forces genomes to behave as a natural "Maxwell Demon," within a fixed environment, genomic complexity is forced to increase.

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Figures

Figure 1
Figure 1
Typical Avida organisms, extracted at 2,991 (A) and 3,194 (B) generations, respectively, into an evolutionary experiment. Each site is color-coded according to the entropy of that site (see color bar). Red sites are highly variable whereas blue sites are conserved. The organisms have been extracted just before and after a major evolutionary transition.
Figure 2
Figure 2
Progression of per-site entropy for all 100 sites throughout an Avida experiment, with time measured in “updates” (see Methods). A generation corresponds to between 5 and 10 updates, depending on the gestation time of the organism.
Figure 3
Figure 3
(A) Total entropy per program as a function of evolutionary time. (B) Fitness of the most abundant genotype as a function of time. Evolutionary transitions are identified with short periods in which the entropy drops sharply, and fitness jumps. Vertical dashed lines indicate the moments at which the genomes in Fig. 1 A and B were dominant.
Figure 4
Figure 4
Complexity as a function of time, calculated according to Eq. 4. Vertical dashed lines are as in Fig. 3.
See this image and copyright information in PMC

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