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Carel van Schaik and Karin Isler explain:

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

Perhaps the most important limitation of brain size is the fact that brain tissue is metabolically very intensive and it, therefore, consumes a lot of energy. The heart, the liver and the kidneys need a similar amount of energy per gram of tissue. However, their size is much more determined by body weight than brain size i.e. it varies much less between species. Other organs, bones, muscles, skin etc. consume per gramme a fraction of the energy the brain consumes (…)

That means that it is more difficult to achieve a certain increase in brain size through natural selection than it is, for example, to achieve an equivalent increase in muscle mass or general body size.

Another difficulty is that an organism cannot temporarily shut down its brain to save energy because the brain needs exactly the same amount of energy at rest.
(Carel van Schaik, Karin Isler 2010: Gehirne, Le­bens­läufe und die Evolu­tion des Menschen, in: Fischer/ Wiegandt: Evolution, pp. 142-169, pp. 153s)

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III.     The brain

Hypothesis 9

The “expensive” brain

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


The brain is a very expensive organ for a living organism because it consumes a lot of energy. Nevertheless, in mammals, primates, monkeys, great apes and finally hominids all the way up to humans, a steady increase in relative brain size can be observed.

Explanation:

In the beginning, two statistics related to energy consumption should make the costs of the brain clear: 1. The brain is responsible for approximately 20% of the total energy consumption of the body. 2. More than 50% of the energy that the human foetus absorbs is used to build up its brain.

Now three authors who have weighed in on the issue of the costs of the brain in the context of human evolution will have their say. Robin Dunbar, from whom I used the first percentage, wrote:

Brain tissue is unusually expensive to grow and maintain. It needs about ten times more energy than one would expect, based on its weight, and it is the most expensive tissue after that of the heart and liver.

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With the emergence of human culture and the cultural ability of modern humans, something new and unprecedented is emerging.

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


Why does culture develop? The mind? What are the reasons? What is the cause for this innovation that will fundamentally change the world of the human species? How did the brain become the basis of the human mind through a functional change?

The second question: What is new? How can we specifically describe the new issues that arise? In his review of Tomasello’s book The Origins of Human Communication, Jürgen Habermas writes:

After the increases in size of the human brain had stopped, cultural learning processes replaced genetic adaptation. What other animal species lack is the transfer of symbolically stored knowledge from generation to generation, such that it can be revised and expanded in the light of new experiences.
(Jürgen Habermas 2009; Es beginnt mit dem Zeigefinger, in: DIE ZEIT No. 51/2009 of 10 December 2009, p. 45)

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Hypothesis 8

The biological causes

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


The first task is to describe the biological mechanisms that led to the development of the human brain. The biological causes for the development of the human brain, brain growth and the end of thereof must be explained before the beginning of the cultural achievements of Homo sapiens are explored.

The second task is to describe how the existing human brain, through a functional change, could become the biological basis of the mind.

Explanation:

If I can’t make out the details of an object well enough, I would make use of a magnifying glass. If I still want to be able to see finer details or material structures, then I’ll use a microscope. If I want to research a subject scientifically, one possible method is to divide the subject into many small problem areas, each of which can then be examined individually. In the end, the results are combined once again.

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If the brain is the biological seat of the mind, the two are therefore not identical to each other.

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


Moreover, the mind has its own identity, which must be explored and described. The basic form of the mind or culture arose in a special historical situation. With the mind a new level of existence was born,

emergent characteristics of individuals and social groups arose; characteristics that can no longer be adequately described with the biological theory framework but which require the use of humanities or social science theories.

In The Cultural Origins of Human Cognition, Michael Tomasello drew attention to what, on an evolutionary scale, was a short period of up to 250,000 years, during which man’s cultural development has taken place up to this day.

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We know from embryonic development, and Darwin has stressed in great detail that

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


conclusions about phylogenesis can be drawn from the ontogenesis of individuals of today. Why shouldn’t this line of reasoning be applied to brain and mind?

Every infant already has a human brain before it can absorb cultural stimulation from its environment. This should also apply for phylogeny, the tribal history of humans. The chronological sequence of brain and mind development is basic but raises new questions about the development of the brain.

From the moment the human brain exists in its present form, there is the possibility of the emergence of the human mind and human culture – but only the possibility.

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II.      The solution

Hypothesis 7

The succession of brain and mind

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


As the basis of the human mind, the human brain is an evolutionary innovation that couldn’t have developed gradually but rather only through a change of function. The co-evolution of mind and brain is replaced by another model of thinking, that of the temporal succession:

First the human brain developed, then the human mind developed. First the human brain had to be created for biological reasons. Only then could the human brain become the basis of the human mind through a change in function.

Explanation:

The biological basis of the human mind is the human brain. Therefore, the development of the human brain is a central question in the development of human culture and the human mind.

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