Harnessing Randomness: Denis Noble's Insights on Biological Order
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Chapter 1: The Interplay of Order and Disorder
In an earlier discussion, I delved into the concepts of order and disorder within physics, showcasing how these elements can emerge from one another. This ongoing dialogue about order versus disorder, as well as randomness and structure, has been a frequent topic with Benedict Rattigan. With the upcoming symmetry exhibition at the British Museum, I felt it was timely to share Denis Noble's perspectives on how these principles interact within biological contexts.
Within biological systems, mechanisms have evolved to counteract randomness. For instance, neurons must minimize signal noise during electrical impulse transmission to ensure clarity in our brain's processing. Conversely, in fascinating cases, certain organisms exploit randomness to create new functions that enhance their survival in changing environments.
This concept of utilizing randomness is reminiscent of optimizing the ‘learning rate’ in reinforcement learning. Take, for example, the classic bandit problem where one must deduce the distribution of rewards from selecting among several slot machines. Initially, a higher degree of randomness is beneficial to explore the options before zeroing in on the most rewarding choice.
Before advancing, I want to address the ‘neo-Darwinian’ viewpoint regarding randomness in evolution. This perspective posits that variations among organisms are random and, in themselves, lack functional purpose. By functional, I refer to the idea that organisms do not actively use randomness to improve their survival odds. Instead, this randomness is seen as a passive element in the natural selection process, where advantageous mutations are retained through chance occurrences.
Noble refers to this notion as "blind stochasticity," indicating that genetic variations happen randomly and are not purposefully utilized. These mutations arise incidentally, influenced by environmental noise, and natural selection subsequently determines their viability.
Section 1.1: Randomness with Intent
Noble contends that there are instances where randomness is employed purposefully, rather than merely as a passive factor. In evolutionary biology, the function of an object or process that has evolved through natural selection serves a clear purpose. In physiology, this function translates to intent. Noble cites studies that illustrate how organisms leverage randomness to respond effectively to heightened environmental stress. This could be likened to an ‘explore’ mode in the aforementioned bandit problem—when faced with challenges, organisms increasingly depend on randomness to discover viable solutions.
Several examples highlight this phenomenon:
- Cells can harness randomness to accelerate mutation rates and generate new functions.
- Cell populations manage their random distributions effectively.
Noble refers to a study demonstrating that cells taken from extreme points within a population's distribution retain a ‘memory’ of their origins. This is particularly intriguing, as one might expect that bacteria sampled from the extremes would lack knowledge about their overall distribution.
Moreover, it has been observed that mutation rates in certain genomic regions can speed up under specific environmental pressures. This suggests a targeted mechanism at play, enhancing the rate of genetic adaptations. Noble presents two key examples. Firstly, in the immune system, the mutation rate in variable genomic regions increases when responding to new antigens. Secondly, certain bacteria experience a remarkable five-order magnitude acceleration in genomic reorganizations to cope with additional stress. A notable illustration of this accelerated mutation is seen in the FC40 strain of Escherichia coli, where mutations arise at a high frequency when exposed to lactose as the sole carbon source.
The first video, "Order and Disorder in Biological Structures," explores how biological systems manage the balance of order and randomness, echoing Noble's ideas on adaptation.
The second video, "Order and Disorder," delves further into the implications of randomness in evolution and survival strategies in living organisms.