Another phenomenon that Achim Peters describes is body downsizing,

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

a phenomenon that can already be detected in lower vertebrates such as fish. When food shortages or a protracted illness occur, tissue recedes. Peters:

In the history of the human species, which ranges from Homo Australopithecus to Homo erectus to us, there were long periods of crisis such as ice ages and periods of drought (…)

If we look at the era some 50,000 years ago as an example of such a long-term supply crisis in the tribal history of humans, it perhaps provides us with the reason why the human body underwent such a sustained transformation, became more delicate, therefore providing the brain with greater access to energy in modern Homo sapiens. This is supported by the fact that about 50,000 years ago, with the beginning of the last ice age, progressive body downsizing began. (p. 49)

Hypothesis 9 dealt with the special position of the brain among the organs of animals and humans. The high energy consumption makes it a risky organ for living beings. The effort is only worthwhile if there are major advantages that offset the negatives.

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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.

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