Review 1 - The evolutionary origin of complex features

From: Anna Cavender (cavender@cs.washington.edu)
Date: Wed Dec 01 2004 - 12:02:17 PST

  • Next message: Ankur Jain: "Review"

    The evolutionary origin of complex features

    Richard E. Lenski, Charles Ofria, Robert T. Pennock, Christoph Adami

    One line summary:

    This article describes the creation and evaluation of digital organisms:
    objects that can reproduce, mutate, and compete in a digital environment
    simulating the evolutionary theories of Darwin.

    The two most important ideas in the paper:

    Digital organisms mutate by imperfectly copying their instructions
    resulting in two different child organisms. They receive rewards of
    “energy” when mutations result in specific, predefined logic
    instructions of varying complexity. The energy is needed for the
    organism to execute instructions. In this way, only the “good” organisms
    acquire enough energy to continue execution. This implicit selection
    allows a positive evolution where descendants obtain more and more
    complex features.

    Experiments show that achievement of simple functions was often a
    prerequisite to more complex features and that often backward or harmful
    mutations actually yielded highly beneficial mutations in later descendants.

    The authors claim that these findings confirm evolutionary theories
    proposed by Darwin.

    The one or two largest flaws in the paper:

    Darwinian theories argue that evolution is based on survival of the
    fittest; however this paper based evolution on the successful execution
    of predefined logic functions in a static environment. While their
    findings are quite interesting and mesh well with Darwinian Theory, the
    reader is left wondering about the ecological validity of these
    findings. First, it is unclear that predefined rewards occur in nature,
    and second, natural evolution occurs in a changing environment.

    Another flaw may be a small point, but a point I found unclear. Since an
    organism consists of a list of instructions, it seems that logic
    instructions (functions) could persist through mutations even though
    other functions are acquired. This is confirmed in the description of a
    situation where the acquisition of new instructions outweighs the loss
    of existing instructions. However, I’m unsure why the authors consider
    these losses deleterious if the organism will no longer receive rewards
    for executing old instructions: there is no motivation to keep them around.

    Two important open research questions on the topic:

    As indicated by the authors, an sexual versus asexual reproduction could
    be analyzed, however the genetic aspect of choosing feature inheritance
    may add to the “stacking of the deck” aspect of the study.

    An interesting modification to this study would be one where the
    environment (or the definition of success) where to change over time.

    Another area for future research would be a less random mutation scheme
    where external factors (environment, previous mutation choices,
    knowledge about mutations that yield a reward of more energy) could be
    used to decide genetic function.


  • Next message: Ankur Jain: "Review"

    This archive was generated by hypermail 2.1.6 : Wed Dec 01 2004 - 12:02:23 PST