In an earlier essay, I explained how the presence of reserve capacity and slack at the component level can cause fragility at the level of the system. Although I argued that degeneracy, i.e. the existence of multi-functional components with partially overlapping functions, is superior to simple redundancy/slack, this does not imply that degeneracy or adaptability at the component level is sufficient to prevent this problem. There are no magic bullets in the realm of complex adaptive systems and every solution comes with its own tradeoffs. The human body presents us with many examples of this.
The Pancreas
The best example of the downside of simple slack/redundancy is the pancreas. The pancreas consumes a relatively small percentage of our body’s resource consumption (unlike, for example, the kidney, liver and small intestine) which is why it maintains a 10x reserve capacity/safety factor in its primary function of enzyme secretion. The pancreas also does not possess the ability to regenerate after damage unlike other organs such as the liver. Yet this is precisely the reason that “malabsorption, due to decreased absorption of ingested food by pancreatic proteases and lipases, is not observed until pancreatic enzyme output has dropped to only 10% of normal peak values” and why pancreatic cancer is so difficult to detect. By the time we can detect the symptoms of malabsorption, pancreatic cancer has typically metastasised to other organs.
The Liver
Unlike the pancreas, the liver does consume a significant proportion of the body’s resources and therefore, it only maintains a reserve capacity of around 2x its normal load. However, the liver also possesses the ability to regenerate and recover from damage to an incredible degree. But this regenerative ability also comes with a sting in the tail. Fatty liver disease is often described as a silent killer because the disease shows no symptoms until the liver is severely damaged1. Fatty liver disease is, of course, also an example of an evolutionary mismatch disease which just goes to show that there are limits to how adaptable any system can be.
The Brain
The brain is the quintessential example of a resilient organ. One of the most impressive features of the brain is its ability to adapt to partial damage. Some of the most extreme examples come from John Lorber’s work on patients with cerebral cortex losses due to hydrocephalus. In one of Lorber’s more dramatic cases, a student had an IQ of 126 and a Mathematics Degree with barely any brain matter (the cortex being reduced due to hydrocephalus). There are many other such examples - Huntingdon’s disease patients can lose 10% of their brain tissue without cognitive impairment.
The primary reason for the resilience of the brain is its degeneracy i.e. “the ability of structurally different mechanisms to yield the same output”.
degeneracy clearly underlies recovery by providing robustness to failure or damage. When degenerate sets of neuronal systems are available,damage to one system does not impair response accuracy, which is retained by virtue of the remaining systems. Response times might be affected but might also recover rapidly following compensatory adjustments within the remaining systems.Degeneracy also enables new learning because previous learning, which is embodied in the other systems, is not lost following plastic changes to any single system. This general robustness to either local damage or new learning, is closely related to ‘graceful degradation’ in the context of parallel distributed systems.
Nevertheless, this degeneracy and robustness to failure also comes with its own set of drawbacks. Many degenerative diseases of the brain, such as dementia, are extremely difficult to detect in their initial stages as the brain continues to function more or less normally in the early stages of these diseases and “by the time a patient has symptoms like mild cognitive impairment with memory decline, his loss of key neurons is profound”2.
Many of our organs maintain significant slack, adaptive capacity and degeneracy. But their resilience carries with it an inevitable cost in increased fragility under certain scenarios. Resilience against moderate disturbances can increase fragility when faced with more severe disturbances. Also, component-level resilience can mask deterioration within the system and allows undetected, latent failures to build up which increases the risk of undetected catastrophic system failure, i.e. micro-resilience leads to macro-fragility.
Kenneth Mossman in ‘The Complexity Paradox’ referencing https://pubmed.ncbi.nlm.nih.gov/15734687/