Artificial Life and Catastrophe Soup

24 August, 2008

The Telegraph reports an observation from Prof Mark Bedau at a recent Artificial Life conference that developments in simulated evolution over the last twenty years have not been as fruitful as originally hoped. Whilst insisting this did not in any way support an intelligent design hypothesis, which prompted a flurry of related blog posts, he did say we needed more understanding of the self-organisation processes involved.

These simulated evolution experiments are finding equilibrium states which are not conducive to evolving higher organisms. Complex life-forms never emerge due to the dominance of very simple parasitic organisms like viruses. One imagines genetic algorithms starting from a random state and exploring the local fitness landscape before settling into fairly stable configurations which only allow minor mutations to survive. Punctuationist evolutionary theory holds that evolution happens at a variable rate, and this is related to extinction cascades within the ecosystem. The magnitude of cascades are distributed by a power law, and the largest result in mass extinctions which provide rich opportunities for evolution to occur rapidly, by vacating niches previously occupied by dominant species.

However, the extinction cascades which result from mutation may not be enough to avoid homeostasis. The Gaia Hypothesis observed that the biosphere is a system of both living organisms and the environment. Organisms cannot be decoupled from the carbon and water cycles. They shape the environment by changing its structure and components, but more importantly environmental changes also instigate massive extinction cascades. If this were not the case, perhaps the Earth would still be ruled by dinosaurs or blue-green algae.

If homeostasis occurs in an evolutionary model then maybe expecting a killer virus to provide wiggle-room for creativity is not enough. Volcanoes, asteroids, ice ages and other environmental impacts must be included in the system. These events change the topology of the fitness landscape. This means that what was previously a good adaptation may now be a disadvantage. This massively relaxes the niche pressure on the survivors, which allows new maxima to be reached. Global optimization problems can be addressed by an approach like Simulated Annealing, which is something akin to shaking a bucket of stones to bring the large ones to the surface. Add some randomness to break the order, so that new structures may be formed. However, the magnitude of extinction events needs to to be distributed properly – there have to be some huge ones. Even the human population has veered close to extinction on several occasions. Most notably we were apparently reduced to something like 10,000 individuals when a supervolcano at Lake Toba erupted about 70,000 years ago.

When a forest is felled there is much room for growth, but biodiversity is hugely reduced since species provide each other’s environment. The ecosystem must bootstrap itself. Storms and forest fires provide catastrophes on the intermediate scale. Minor adjustments are made when a single tree falls and creates a clearing, giving a small window of opportunity to other plants. Meanwhile, a garden sometimes requires drastic tree surgery in order to reduce shade, but this can usually be avoided with regular attention to pruning. Without catastrophes we might still be soup… the question is, can the effects of major impacts on a system ever be simulated with directed minor adjustments? In the context of social media or organisational knowledge management, can revolutions ever be achieved through incremental change? And can Google be beaten by a head-on assault, or does the playing field have to first be redefined?

Homeostasis in Social Networks

4 August, 2008

As a network grows and develops a power law distribution of connectivity, the resulting structure is heavily biased towards the initial nodes by virtue of their prior existence. Social networks therefore tend to be disproportionately dominated by the individuals who have been around the longest. This state is very stable, since information flow on the network is highly dependent on these hubs. However, the imbalance of attention may result in potentially valuable new members being neglected or moving elsewhere. Stagnation as a consequence of homeostasis might be one reason why one network gives way to another.

In living organisms a stable structure is desirable, and homeostatic mechanisms are present to maintain equilibrium. However, if an organism cannot break out of a given equilibrium state it may prove brittle and vulnerable to external pressures. The birth and death of individuals allows a tribe or species to adapt to a changing external environment. An alternative response to environmental changes is exhibited by cellular slime molds which, when food is scarce, merge into a “multicellular slug-like coordinated creature which crawls to an open lit place and grows into a fruiting body. Some of the amoebae become spores to begin the next generation, but some… sacrifice themselves to become a dead stalk, lifting the spores up into the air.”

Corporations and other large organisations also suffer from the effects of homeostasis. Although there is an entire industry devoted to the study of organisational structural dynamics and change management, stagnation is more often than not alleviated by market pressures, whether by acquisition or enforced “restructuring”. In our work lives we are each happy to accept a comfortable equilibrium state, but this reduces the ability of the organisation to adapt. And of course, when nation states are too rigid and authoritarian they tend to fall to revolution rather than evolution.

In the brain homeostasis might correspond to boredom resulting from a lack of stimulation. This reaction is perhaps intended to instigate a search for new ideas or experiences, which are generally rewarded by a feeling of pleasure. If something is new and exciting it’s usually fun too, because we enjoy learning. The desire for novelty provides a mechanism to move the mind out of an unhelpful state.

If a garden is left to nature, a power law distribution of species quickly develops. One or two particularly well-suited or vigorous plants take over whilst others dwindle. Gardeners address this by weeding and pruning. Even “wild gardens” require the careful application of a little encouragement and discouragement. When a new plant appears it must be nurtured whilst the weeds are kept in check.

If social sites like Digg, Wikipedia and Twitter are to remain dynamic and continually evolving they need to solve the homeostasis problem. In the social media, new and interesting contexts or individuals with novel viewpoints should somehow be amplified. There has been recent discussion on Twitter about how a modified Retweet could be useful, and perhaps this partly fulfills the need since the resulting amplification is relative to the connectivity of the sender, but it ultimately depends on the goodwill of community members. I have mentioned in previous posts how novelty can be identified with semantic profiling, but how can it be “subtly encouraged” without threatening the social ecosystem in question?