In evolution, however, the enlargement of the brain has not only taken place in apes and hominids

Parade, Cusco, Peru, 27. 8. 1989
Parade, Cusco, Peru, 27. 8. 1989

but also seems to be a general principle of evolution. Carel van Schaik and Karin Isler explain the problems that animals have with the growth and maintenance of their brains and then write:

Therefore, there are good reasons to assume that each animal species has the largest brain that it can energetically afford. Despite these costs, brain size has gradually increased over evolutionary periods. This is what palaeontologists call the Law of Marsh. It was formulated as early as 1879. (p. 155)

To regulate the energy of the human brain, Achim Peters formulated the Selfish Brain Theory, which is important in our context.

The idea of the Selfish Brain is that the brain regulates the energy distribution within the body as well as between the body and the brain itself. It always first ensures that it has ample energy supply. Peters writes that this theory is based

on two fundamental pillars:
– The brain first regulates its own energy level. To do that, it activates its own stress system, which draws energy from the body’s own reserves.

– Then the stress system returns to its rest position. Now food intake takes place in order to replenish the body’s reserves (the traffic light shows green towards the body).
(Achim Peters 2011: Das egoistische Gehirn, Berlin, p. 32)

Peters explains the evolutionary significance of brain egoism:

As we will see later on, however, the egoism of the brain is not an end in and of itself, rather it provides us with certain evolutionary advantages. Prehistoric humans were constantly threatened by food shortages and environmental hazards – a problem that has continued well into this day and age. In order to be able to react appropriately, it was particularly important that the brain functioned properly.

Perception had to be sharpened. The right decisions had to be made in dangerous situations. And it was important to know where to find food in times of shortage. So the motto was: All power to HQ! These mechanisms, which guaranteed us good brain performance in times of food shortage, still work in us today. (p. 33)

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