… it doesn’t evolve.
Remember when AVIDA proved Darwin right?
These results provide evidence that low-impact mutations can present a substantial barrier to progressive evolution by natural selection. Understanding mutation is of primary importance, as selection depends on the mutational production of new genotypes. Numerous changes that would be beneficial may nevertheless fail to occur because mutation cannot produce them in the time available.
Further, it is important for biologists to realistically appraise what selection can and cannot do under various circumstances. Selection may neither be necessary nor sufficient to explain numerous genomic or cellular features of complex organisms [2-4].
PDF and poster here:
Nelson CW, Sanford JC (2011) The effects of low-impact mutations in digital organisms. Theoretical Biology and Medical Modelling 8:9.
Nelson CW (2011) Selection threshold constrains adaptive evolution in computational evolution experiments. Great Lakes Bioinformatics Conference. F1000 Research 2:A13.
We feel this work uses Avida to demonstrate that the selection threshold and resultant genetic entropy, and also irreducible complexity, can be prohibitive to progressive evolution. Some highlights from the Conclusions:
“… there are several ways in which Avida’s default settings produce results which conflict with observations from biological experiments. Precursors necessary for the most complex logic operation in the program, EQU, are frequently produced by random mutation, yet confer very large fitness rewards. Fitness effects of beneficial mutations under Avida’s default settings range from 1.0 to 31.0, values that are extremely rare in the natural world. As a result, fitness increases by an average of 20 million in only 10,000 generations. This is roughly seven orders of magnitude greater than the changes observed in biological evolution experiments.
… most mutations in biological organisms are low-impact [29], and this class of mutations may dominate evolutionary change [1,2]. When Avida is used with more realistic mutational fitness effects, it demonstrates a clear selection threshold. Mutations that influence fitness by approximately 20% or less come to be dominated by random genetic drift. Mutations that affect fitness by 7.5 – 10.0% or less are entirely invisible to selection in this system. These results provide evidence that low-impact mutations can present a substantial barrier to progressive evolution by natural selection. Understanding mutation is of primary importance, as selection depends on the mutational production of new genotypes. Numerous changes that would be beneficial may nevertheless fail to occur because mutation cannot produce them in the time available.
Further, it is important for biologists to realistically appraise what selection can and cannot do under various circumstances. Selection may neither be necessary nor sufficient to explain numerous genomic or cellular features of complex organisms [2-4].
… The accumulation of slightly deleterious mutations may pose an important health risk for numerous species, including humans [74], and warrants further study using computational approaches… we recommend that future experiments with digital organisms employ more biologically relevant mutational fitness effects.”