Why did brains evolve, anyway?
Part 6 of Is “Is the brain a computer?” even a good question?
It’s too late to change the answer, and it distracts from the really useful questions about the relations between computers and brains. Nevertheless, a deeper look finds that brains stretch the definition of computing, perhaps beyond the breaking point.
This is part 6 of a series of brief essays (sometimes very brief) on aspects of this question. Part 1 contains the introduction and an index to the whole series.
Why did brains evolve, anyway?
What is the adaptive advantage to having a brain? The evolutionary precursors of human brains didn’t deal with anything like numbers, and could obtain no survival value from performing computational operations like long division, or even symbolic operations like organizing syllables into sentences. But efficiently organizing physiological and behavioral activity, that is, acting as a system controller, provides multitudes of advantages at all levels of organism complexity throughout its species’ history. The cells of a multicellular organism can react to environmental changes and to changes originating in other cells in a purely local way, with global responses propagating from one part of the organism to another via diffusive processes, but these reactions are slow. For best survival, an organism needs to coordinate its own behavior at a rate faster than the rate of change in the environment. Once an ecosystem acquires organisms with predator-prey relationships, ability to react faster and smarter than an adversarial organism becomes a life or death advantage.
Nervous systems improve the organism’s intercellular coordination situation by enabling cells that aren’t adjacent to each other to react together to a localized stimulus. Non-neural interconnection systems such as vascular systems are an improvement over cell-by-cell propagation of responses, but having specialized cellular structures, and even dedicated cell types, that can swiftly carry signals beyond a cell’s immediate nearest neighbors, and skip over intermediate cells, will provide even greater advantages.
Once a species has evolved rapid communication between distant cells, the math of networking provides a way to obtain a further advantage. In order to connect every cell to every other cell, n² connections are required. But with a centralized routing and processing center, only n connections are needed, providing a substantial complexity and metabolic advantage. However, when processing and transmission speeds are slower than the rate of change of the environment, organisms that can perform stimulus processing closer to the sensory transducer will have a response-time advantage. This tradeoff can lead to hierarchies of processing involving both brain-based responses and more local responses such as spinal reflexes, and to the neural nets that operate octopus arms.
The tradeoffs between the speed of processing and the speed of transmission between processing elements have been influential in the evolution of electronic computer architectures, as well. While access to CPU registers is measured in nanoseconds,access to the dynamic RAM of main memory is measured in microseconds, access to long term storage in disk memory may take milliseconds, and it may take dozens of seconds to retrieve a block of data stored offline in a robotic tape library. This has led to the development of elaborate hierarchies of memory systems, with up to three levels of caching between register memory and RAM memory, and sophisticated prefetching and resequencing algorithms for optimizing retrieval sequences in order to maximize data throughput in the face of delays for disk head movements and tape movements.
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