review1 : The evolutionary origin of complex features

From: Beltran Ibarra Davila-Armero (bida@cs.washington.edu)
Date: Wed Dec 01 2004 - 02:23:55 PST

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      The evolutionary origin of complex features

    By Richard E. Lenski, Charles Ofria, Robert T. Pennock and Christophe Adami

    This paper aims to prove Darwin’s theory of evolution through the
    simulation of an evolving population of digital organisms that meet the
    three necessary conditions for evolution: replication, mutation and
    competition.

    One of the main ideas is that complex features can derive from simple
    ones. After the results explained all along the article, we can clearly
    see that although they always start with a population which is unable to
    “do” anything (no logical functions), they always end up getting the
    most complex feature (the EQU function). Moreover, this achievement was
    done albeit the fact that several mutations were needed to perform a
    simple intermediate function.

    A second idea expressed in the article is that the reward system was
    necessary to complete the most complex feature. In fact, when they
    rewarded only the EQU logical function, none of the populations evolved
    to EQU, whereas a bit more than 34% achieve this in the reward-all
    system. This reward system shows that somehow organisms need to be
    “guided” through intermediate steps (the rewarding of simple functions)
    in order to achieve more complex status.

    Another interesting point is that all this experimentation proves that
    the evolution theory based on the three precepts (mutation, replication
    and competition) works. The evolution of each population has been under
    those rules and has evolved by eliminating the weakest elements, just as
    Darwin advocates.

    As far as flaws are concerned, one point that is subject to comment is
    the way the authors assert that digital experimentation is good enough
    to allow results from these to be applied into the biological world. The
    nature is somehow far more complex than simple organisms that operate
    logical functions and there are more environmental factors that
    influence the evolution of a population. It is maybe a little too
    simplistic.

    Another point is that Darwin’s theory of evolution is concerns all
    organisms: sexual and asexual. This article only takes into account
    asexual ones and leaves out the sexual ones. It could be a weak point in
    their procedure because maybe the sexual organisms fail to come to the
    same levels of complexity because of the higher mixing of phenotypes.

    Some points were not very clear about what pivotal mutations are.
    Although they give an explanation of these, they are not very precise
    and they don’t explain how they calculate or come up with these specific
    mutations. This is even more blurry because, as it is said, there are
    not “must have” functions to achieve the most complex one.

    Of course the first question that we can develop is how well this
    demonstrates the theory of evolution and what are exactly the origins of
    life. And on the other side are we able to predict how populations will
    evolve. Maybe if the good reward functions were taken and a good pattern
    of an accurate set of ancestors was implemented….

    This is clearly a search problem with its state space (all the possible
    the genotypes), and its heuristics (the rewarding functions). Somehow
    there is some randomisation since deletion is acceptable (by deleting
    some functions we lose some logical functions and fitness). Maybe we
    could compare it to some local search (hill climbing) with side moves
    which will allow moving down the slope.


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