on brain size: The radiator hypothesis.

The radiator hypothesis: A theory in “vein — Arizona …
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T2 - Behavioral and Brain Sciences

However, even if some human populations do have larger colons and guts, I would still predict that modem humans as a species have a small gut for their body mass. In my opinion, when using an evolutionary per- spective it is always best to try to account for both the how and the why, since the two are intertwined (Milton 1988). As is pointed out by Jerison (1973)~ primates ap- pear to have been relatively large-brained mammals since the inception of the order, which suggests that they have long tended to seek behavioral (brain-based) solutions to their dietary problems and thus have long been able to "afford" the mental solution-that is, afford to have a somewhat large brain relative to body mass. I have proposed that this came about because the ances- tral lineage ultimately leading to Primates was some- how able to enter the as-yet-unfilled arboreal plant- based dietary niche provided by tropical-forest angiosperm trees and vines and then radiate in such a way as eventually to control a large proportion of the highest-quality plant foods (new leaves, ripe fruits, and flowers) in this arboreal environment (Milton 1987:94- 95). Entry into this dietary niche appears to place consid- erable pressure on the feeder to lower the costs associ- ated with procurement of these patchily distributed plant foods-a solution which in our order appears to have been resolved in large part by the development of cerebral complexity, with the attendant behavioral plas- ticity, memory, learning, and social skills required to lower food acquisition costs and improve foraging re- AND WHEELER The Expensive-Tissue Hypothesis I 21 5

> This is known as the "radiator hypothesis" or the "brain-cooling > hypothesis," which can be tested
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• However, the expensive brain hypothesis may have some merit ..

So, your Chevy radiator and its parts must be checked regularly to be sure that it is working
CONSTRAINTS ON BRAIN SIZE: THE RADIATOR HYPOTHESIS
A.

Aristotle said emotions were in the heart (cardiac hypothesis), and the brain was a radiator for blood
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In a nutshell, the expensive-tissue hypothesis pro- poses that a high-quality diet permitted a relatively smaller gut and thereby relaxed a metabolic constraint on brain size. Elsewhere, I have proposed another physi- ological/anatomical complex as a prime releaser of brain size in the genus Homo, namely, evolution of a network of cranial veins (a "radiator") that serves to cool the brain under conditions of hyperthermia (Falk 1990). Here I suggest that the two hypothetical releasers are com~atible because cerebral metabolism, relative brain sizelaand thermolytic needs are all intertwined. If both releasers were instrumental during hominid evolution, perhaps the underlying behavioral factors (diet for me- tabolism, locomotion for vascular evolution) may be wo- ven into a satisfying (if not falsifiable) scenario.

Consistent with the radiator hypothesis of human brain evolution (see Falk 1990), the respiratory and arterial ..
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