Piero Scaruffi(Copyright © 2013 Piero Scaruffi | Legal restrictions )
These are excerpts and elaborations from my book "The Nature of Consciousness"
The Heat Engine Of The Body
The Spanish neurologist Francisco Mora introduced a simple vision for what brains do for us: they regulate our temperature.
From the beginning life was capable of reacting to temperature: even the earliest unicellular organisms must have been capable of sensing heat and cold.
Heat, after all, was the primeval source of energy for living organisms. These organisms required heat to survive and the main source of heat came from the environment. The progenitors of the living cell, the "protocells", were probably units of energy conversion, converting heat into motion, just like a heat engine. In 1995 the Dutch chemist Anthonie Mueller, the proponent of "thermosynthesis", showed that such systems could form spontaneously in the primordial conditions of the Earth.
If they survived, these organisms must have developed a way to react to positive and negative stimuli, such as correct or excessive amount of heat. The early nervous systems were assemblies made of cells already capable of sensing and reacting to temperature. Proof is that all known organisms, including unicellular ones, are capable of avoiding adverse environmental temperatures. In other words, throughout evolution all organisms were capable of sensing external temperature.
Mora speculates that during the transition from water to land (from stable temperature to wildly variable temperature) the nervous system must have learned to control body temperature. Nocturnal animals must have developed also a means to overcome the loss of environmental heat and produce heat internally. And the autonomic control of temperature was born.
This feature allowed the evolution from cold-blooded animals (animals whose temperature fluctuates with the temperature of the environment, whose only sources of heat are external sources) to warm-blooded animals (animals that maintain constant body temperature by producing heat internally). Cold-blooded animals are dependent on environmental heat: when ambient temperature rises, they are active and seek food; when ambient temperature decreases, their motor activity slows down. Warm-blooded animals overcame this limitation thanks to that self-regulating feature, thanks to the ability of producing heat internally when heat from outside is not enough. And they freed themselves from their habitat: they were capable of changing habitat because they were capable of maintaining their body temperature regardless of changes in the external supply of heat.
A very efficient self-regulating heat engine that maintains constant temperature opens up new opportunities for evolution: one organ that benefited was the brain, that could grow to its actual size and complexity. If it didn't have an adequate supply of energy, the brain would not be capable of performing the tasks it performs. A hot organ is required for thinking.
Modern mammals, who have the highest demand for internally produced heat, regulate temperature through a whole system of thermostats, not just one. Experiments have proved that mammals have not one but many centers of control of body temperature: in the spinal cord, in the brainstem, in the limbic system and mainly in the hypothalamus. Rather than one point of control, this is more like a complex system, that peaks in the hypothalamus.
It is a very accurate system: humans can survive only in a narrow temperature range (a few degrees below or over 37 degrees Celsius a human body becomes a dead body). Why regulate at 37 degrees instead of, say, 20? It turns out that 37 degrees is the ideal temperature for balancing heat production and heat loss.
Ultimately, the brain is responsible for maintaining a constant temperature, the very constant temperature that allows the brain to function.
At the same time, the brain was made possible by a cooling mechanism. Humans are among the few mammals (and the only primates) with a naked skin. Mammals that have a naked skin are usually big: having naked skin helps "cool down" the body and therefore avoid the risk of overheating (overheating would, in particular, damage the brain). Humans, however, cool down by sweating. The US anthropologist Nina Jablonski argued that cooling via sweating enabled the large (heat-producing) brains of humans.
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