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The Curse of a Big Head

Copyright 1996 G.R. Morton. This can be freely copied and distributed if unaltered and no monetary charge is made.

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[I include this on the web page because of the fascinating reaction it received when I posted it on a listserver. One friend thought it was bad theology but couldn't really explain why. One biologist said there were eccrine glands on camels and that they sweated a lot, yet he could not provide a book or article which supported his position. An MD provided evidence that on a per gram basis the heart uses more oxygen than any organ. The brain uses half as much oxygen as the heart on a per gram basis. If oxygen consumption is proportional to heat production, then since the heart weighs 1/5 what the brain does then the brain will produce about 2.5 times the heat of the heart. If anyone wants to provide contrary evidence to the thesis below, I am interested, but only in documented evidence.--grm]

Genesis 3:16-21 (NIV) "To the woman he said, 'I will greatly increase your pains in childbearing; with pain you will give birth to children. Your desire will be for your husband, and he will rule over you.' To Adam he said,

'Because you listened to your wife and ate from the tree about which I commanded you, 'You must not eat of it,' "Cursed is the ground because of you; through painful toil you will eat of it all the days of your life. It will produce thorns and thistles for you, and you will eat the plants of the field. By the sweat of your brow you will eat your food until you return to the ground, since from it you were taken; for dust you are and to dust you will return.' Adam named his wife Eve, because she would become the mother of all the living. The LORD God made garments of skin for Adam and his wife and clothed them."

While I know that large numbers of Christians do not take this account as a piece of history, there is a very interesting set of circumstances in anthropology which ties many of the features of this story together. These features are the pain of childbirth, sweat, and the need for clothing. All of these have a singular cause--a big head. In what follows I will quote the original authors because the experts can say it better than I.

The brain is a huge consumer of energy. Human adults use about 20 percent of their metabolic energy running the brain. (Johanson and Shreeve, p. 263) Left alone the brain would quickly over heat and die. Even modest increases can be fatal; raising the brain temperature to 106 degrees Fahrenheit causes brain damage. This fact means that the brain must be cooled and the temperature stabilized. Physically, there are several ways to accomplish this--heat conduction, convection or a fluid coolant system. Convection only works in fluids and the brain is not fluid and heat conduction through the skull is too slow. The only real solution is a coolant system like an automobile uses. The cooling system must be efficient. Dean Falk, one of the world's leading authorities on hominid brains, advanced a theory in which the hominid brain could not grow any bigger than the cooling system attached to it. The theory originated from a comment by her mechanic. She writes Falk, 1992, p. 156):

"It was an 'aha' experience, if ever I've had one, and the weirdest combination of events led to it. First, the engine in my 1970 Mercedes needed major surgery. I took it to Walter Anwander (a whiz) in Lafayette, Indiana, who completely rebuilt the engine. One day, while enumerating the wonders beneath the hood (about which I definitely needed schooling), Walter pointed to the radiator and told me 'the engine can only be as big as that can cool.' I didn't think much about it at the time."

The brain, like that engine, can only be as big as the cooling system it has. If the brain overheats, the brain is ruined just like overheating a car engine will ruin it. In the brain the blood acts as the coolant. The brain has several emissary veins which go from the interior of the skull to the skin of the face. These veins are part of the "radiator" system. When a person is cold, blood flows from the cranium outward in these veins. But when a person exercises and becomes overheated, the blood flow reverses and blood flows into the cranium. The reason for this reversal is that the skin of the face (the brow included) acts as a radiator, cooling the blood which then enters the brain to cool that organ. Some of the veins are preserved in the skulls of extinct hominids (and man) in the form of emissary foramina (a foramina is a hole in the skull see Falk 1992 p. 153). Thus a record of the size and number of emissary foramina are preserved in ancient skulls for anthropologists to examine. Falk (1992, p. 159) notes:

"It was beautiful. For the past two million years, the increase in frequencies of emissary foramina kept exact pace with the sharp increase in brain size in Homo. Clearly, the brain and the veins had evolved rapidly and together. I saw that Cabanac's letter was right and that I had unwittingly charted the evolution of a radiator for the brain in my earlier work on emissary foramina. As Anwander had said about my car, the engine can only be as big as the radiator can cool. Apparently, the same is true for heat-sensitive brains."

But emissary veins are only part of the cooling mechanism in mankind. Sweat is the reason that the facial skin cools and the cooling of the skin cools the blood destined for the brain. What do we know about sweat?

The human sweating system is unique among mammals. Bernard Campbell (1974, p. 280-282) describes the function of sweat glands:

"The sweat glands fall into two groups: the apocrine and eccrine glands. The apocrine glands secrete the odorous component of sweat and are primarily scent glands that respond to stress or sexual stimulation. Before the development of artificial scents and deodorants, they no doubt played an important role in human society. In modern man these glands occur only in certain areas of the body, in particular in the armpits, the navel, the anal and genital areas, the nipples, and the ears. Surprisingly enough, glands in the armpits of man are more numerous per unit area than in any other animal. There is no doubt that the function of scent in sexual encounter is of the greatest importance even in the higher primates and man. "The eccrine glands, which are the source of sweat itself, have two functions in primates. Their original function was probably to moisten friction surfaces, such as the volar pads of hand and foot to improve the grip, prevent flaking of the horny layer of the skin, and assist tactile sensitivity. Glands serving that function are also found on the hairless surface of the prehensile tail of New World monkeys and on the knuckles of gorilla and chimpanzee hands, which they use in quadrupedal walking. Glands in these positions are under the control of the brain and adrenal bodies, and in modern man an experience of stress may produce sweaty palms.

"The second and more recently evolved function of the eccrine glands is the lowering of body temperature through the evaporation of sweat on the surface of the body. The hairy skin of monkeys and apes carries eccrine glands, but they are neither so active nor so numerous as in man. Modern man is equipped with between two and five million active sweat glands, and they play a vital part in cooling the body. The heat loss that results from the evaporation of water from a surface is enormously greater than that which could be expected to occur as a result of simple radiation. The fact that sweat contains salt necessitates a constant supply of the mineral if man is to survive in a tropical climate.

"It has been observed that like almost all mammals, primates sweat very little. Even hunting carnivores, such as dogs, lose heat by other means, such as panting. Sweating has evolved as a most important means of heat loss in man, a fact that is surely correlated with the loss of his body hair. The apparent importance in human evolution of achieving an effective means of heat loss indicates without doubt that early man was subject to intense muscular activity, with the production of much metabolic heat; he could not afford even the smallest variation in body temperature. With such a highly evolved brain, the maintenance of a really constant internal environment was a need of prime importance in human evolution."

With this need to dissipate heat in order to maintain a constant brain temperature, hair becomes a problem. Hair traps the sweat and hinders evaporation. Zihlman and Cohn (1986, p. 308) relate:

"How might early hominids have dissipated the heat load generated internally, as well as externally from the sun? One way is through the skin. The skin of modern humans contrasts with that of other, nonhuman primates in four features: 1) humans have a great density (over two million) of functioning eccrine sweat glands over the entire body surface; 2) loss of the apocrine sweat glands has been associated with hair loss, and has occurred except in the ano-genital and axillary regions; 3) hair follicles are diffuse and hair shafts are noticeably reduced in size; 4) skin pigment ranges from dark to light.

"How might these features be interpreted in a functional and evolutionary way? There is the remarkable thermo-regulatory function of eccrine sweat glands. Sweating can deliver two litres of water to the skin surface in two hours and carry off almost 600 calories of heat. Hair tends to trap moisture, so that sweat evaporation is more effective with reduced hair. Interestingly, the number of hair follicles in humans is similar to that in chimpanzees and gorillas, but the much reduced size of hair shafts in humans gives a hairless appearance."

Why do we have hair on our head? Zihlman and Cohn (1988, p. 404) inform us:

"Hair retention on the head is probably important in protecting the scalp from the sun's ultraviolet rays and may assist in stabilizing the temperature of the brain. Human populations are variable in the amount of body hair present, but in all of them the skin surface is hairless enough to permit efficient heat loss from sweating."

Radiatively, hair on the top of the head absorbs the solar heat and re-radiates most of it. An absorbing layer can reduce by half the amount of energy reaching the top of the skull.

When is it likely that mankind needed this cooling mechanism for heat removal? Probably fairly early. For modern men even moderate exertion on the savanna increases the heat production by 100% over the resting levels. Since Homo erectus was as large as we are (Ruff, 1993, p. 56), similar exertions on the plains would yield similar heating. Even the smallest Homo erectus has a brain which is over twice as large as that of the chimpanzee which can get by without sweating. Homo erectus would need to sweat. Since he needed to sweat, then he needed to be relatively hairless as we are.

If he were relatively hairless, then the Homo erectus who lived in Georgia (former USSR Larick and Ciochon, 1996, p. 548-550) would have been ill-equipped to handle the winter temperatures below zero Fahrenheit which occur from time to time in that area. He would have needed clothing. Because of these considerations, Anthropologists like Brian Fagan were forced to conclude (Fagan, 1990 p. 76):

"For Homo erectus to be able to adapt to the more temperate climate of Europe and Asia, it was necessary not only to tame fire but to have both effective shelter and clothing to protect against heat loss. Homo erectus probably survived the winters by maintaining permanent fires, and by storing dried meat and other foods for use in the lean months."

This is a very human set of behaviors and Homo erectus was found in European Georgia 1.6 million years ago.

Now to tie up the final item, pain in childbirth. Among mammals there are two patterns of brain growth. The first pattern is called altriciality. In this pattern the animal is born helpless and extremely immature. The brains of altricial animals are usually half the size of the adult's, and double in size by adulthood. Because of this it takes lots of parental effort to raise the young. Animals following this pattern usually have litters and perform this care for multiple offspring at once. Cats, with their blind and helpless kittens are altricial. The other pattern is precocial. In this pattern the offspring are usually born single and from birth are able to get around quite well. Their brains are nearly adult size at birth. The are alert and all their organs are functioning. An example of this pattern is the horse, the wildebeest etc., where the young will run with the herds within minutes.

Now, according to Walker and Shipman (1996, pp220-222), altricial species almost never have bigger brains than precocial species. The reason is that for all mammals save one, the brain grows rapidly during gestation but then grows less rapidly after birth. There is a kink in the graph of brain size vs. time which occurs at birth. Altricial species whose immature state at birth and subsequent slow down in the rate of growth forever remain behind the more maturely born precocial species.

What humans seem to have accomplished is the trick of keeping the brain growing ar the embryonic rate for one year after birth. Effectively, if humans are a fundamentally precocial species, our gestation is (or should be) 21 months. However, no mother could possibly pass a year old baby's head through the birth canal. Thus, human babies are born "early" to avoid the death of the mother. Walker and Shipman (1996, p. 222) write:

"Humans are simply born too early in their development, at the time when their heads will still fit through their mothers' birth canals. As babies' brains grow, during this extrauterine year of fetal life, so do their bodies. About the time of the infant's first birthday, the period of fetal brain growth terminates, coinciding with the beginnings of speech and the mastery of erect posture and bipedal walking."

This pattern of growth has huge implications. Every other primate doubles their brain weight from birth to adulthood. But due to the early birth of humans, we triple our brain's birth rate. Our last 12 month of fetal growth rate of the brain occurs outside the sensorially deprived womb. The vast quantities of sensory input during the first year of life affects the rate and nature of the neural connections. Because of this year of helplessness, parents must provide close physical and emotional support for the infant. Unlike chimp babies who can cling to their mother's fur, human infants cannot even hang on to mother in spite of having the hand reflex. The mother has no fur because she sweats and she sweats because of a big brain which is why she gives birth to her child early. This early birth then requires the mother to care for the infant and increases the bond between mother and child which partially makes us human.

So, what is the birth pattern in Homo erectus? It is human. Shipman and Walker (1989,p. 388-389) point out that the adult Homo erectus cranial capacity was 950 cc. If they followed the ape-like pattern of doubling their brain size after birth, they would need to be born with a brain size of around 400 cc. Following the discovery of a nearly complete Homo erectus skeleton, the approximate size the erectus birth canal is known. A head with a 400 cc brain is 10 cm too big to fit through the birth canal. Estimates place the maximum fetal brain size able to fit through the erectus birth canal at just 231 cc (Walker and Shipman, 1996, p. 226-227). Homo erectus had a human pattern of birth and must have endured similar pain in childbirth.

[Recent research But this is not all. A recent study of Homo rudolfensis which lived eight hundred thousand years earlier than the 1.6-million-year-old Homo erectus studied by Walker and Shipman above, also had a human birth pattern of trebling its brain size from birth to adulthood. Homo rudolfensis stood about 5 foot 8 inches tall and was quite human in form below the neck (Stanley 1998, p. 164. Steven M. Stanley showed that the birth canal of a Homo rudolfensis would only be able to pass a fetal head of about 210 cc. The adult of this species had brain sizes in the range of 760 to 900 cc. This data would strongly imply that pain in childbirth of the type experienced by human mothers extends back at least 2.4 million years to the initial appearance of Homo rudolfensis. (Stanley, 1998, p. 160-163)

The birth pattern means that Homo rudolfensis children would also be born as helpless as any human or erectus baby which would require long periods intensive care. This would lead to an intense period of bonding between mother and child as also occurs among humans. And the enlarged brain would most likely have meant hairlessness among the rudolfensis also. In short, this birth pattern means they had many of our traits which are theologically associated with the Fall.]

To close, it would appear that there is a single underlying cause of God's curse for the man and woman and it is an increase in brain size. This increase also caused the loss of hair requiring clothing when mankind eventually inhabited northern climes. Homo erectus is found in European Georgia 1.6 million years ago. Without fire or clothing, he would have been unlikely to survive the more severe winters in that area.

The fact that Homo erectus and Homo rudolfensis were saddled with the problems given to Adam and Eve after the fall has theological implications for the status of Homo erectus and Homo rudolfensis, the time during which Adam lived as well as who is eligible for salvation. I have long contended that humanity in the theological sense is much older than most Christians are willing to admit. If sweat and increased pain in childbirth and clothing are not signifying of humanity and the Fall, what then does theologically separate us from mere animals?

It is also intriguing to me that the ancient Hebrew writer would choose as a curse for man and woman, two different maledictions which can be caused by a single phenomenon--an increase in brain size. This single cause also would require the loss of hair and the subsequent need for clothing. There is no way that the Hebrew writer could have had the knowledge to purposefully construct this tale. Is this a fortuitous conjunction of statements or is it divine inspiration?

APPENDIX

The data for the below is from a Jan.1969 Scientific American Article on the Eland and Oryx by Taylor. Desert animals like these should be expected to sweat a lot but they don't.

Eland Sweat

It uses 5.5 liters of water per 100 kg body weight when hot p. 94-95;60 % lost via evaporation. 20% via feces 20 percent via urine. p. 89

5.5*5*.6=16.5 liters per day via evaporation. or 3.3 liters per day per 100 kg body weight. In human terms they sweat 2.268 liters/day (a human weighs 70 kg so there are 7.14 human body masses per eland.

~C.R. Taylor, "The Eland and the Oryx",Scientific American January 1969

Humans are better. humans weigh 70 kg thus there are 7.14 humans in an eland.

"Sweating can deliver two litres of water to the skin surface in two hours and carry off almost 600 calories of heat. "~Adrienne L. Zihlman and B. A. Cohn, "Responses of Hominid Skin to the Savanna," South African Journal of Science, 82:2, (1986), p. 307-308, p. 308

A human supplied with sufficient water and salt can theoretically sweat up to 24 liters over a 12 hour period. This shows the difference between our sweating efficiency and the eland.

ORYX

Oryx weighs 202 kg Grolier's Computer encyclopedia

uses 3 liters water per 100 kg on hot day. p. 95

62% lost through evaporation p.89

2.02*3*.62=3.75 liters per day or 1.87 liters per day per 100 kg body weight. In human terms they sweat 1.299 liters of water per day. (there are 2.88 humans per oryx body mass.)

Sweating efficiency.

The oryx sweats 15 liters/202kg over a 24 hour period. This is .074 liters per kg. At 580 large calories per liter evaporated, this is the removal of 42 calories per kg. Mankind on the other hand can sweat .34 liters/ kg over a 12 hour period (2 liters per hour and 70 kg mass). This is the removal of 197 calories/kg. If we do this in time then the oryx removes 362 calories per hour and man removes 1160 calories per hour. Human sweat is tremendously more efficient by either measure!

As to the need for cooling I took my cannibalistic hamster and measured her. (This vile, nasty little rodent, I call Hannibal after the guy in the movie The Silence of the Lambs. She ate her young.) She can be represented by a cylinder 2.6 cm radius and 15 cm long. My cat, aptly named "Butterball" can be represented by a cylinder 8.4 cm radius and 35 cm long. The hamster has an approximate surface area of .0287 square meters. The cat has .2289 square meters. Their respective volumes are 318 cc for the hamster and 7735 cc for the cat. Lets try to maintain a constant temperature of 25 degrees C in a cylinder of water with these dimensions. Room temperature lets assume is 20 C. Radiation laws say that heat is exchanged is area x sigma *(To-Tr)^4. Sigma=5.67 x 10^-8 watts per meter squared.

Plugging in these values we find using 1 gm/cc:

the cat loses .0037 microjoules per hour per gram.

Hannibal the cannibal loses .0115 microjoules per hour per gram.

The cat has more difficulty losing heat than the hamster on a per gram basis.

Thus, since the oryx is bigger than mankind, he should have more trouble eliminating heat (even if he were naked) and so should need a more efficient heat removal mechanism but he has a less efficient one.

Camel

A camel can only sweat 8.8 liters per day per 100 kg. This is 5104 big calories per day per 100 kg. Mankind is more efficient either per day or per kg. The camel unlike mankind can survive a 14 degree Fahrenheit body temperature rise.

Fur

A furry animal simply cannot have as efficient a sweating mechanism as a hairless one. I will agree that a kg of water evaporated will remove the same amount of heat whether under fur or not. But fur will seriously hinder evaporation. I do not have the data for dogs, but I do have it for camels.

Consider this:

"Their total water expenditure per day was 3 liters per 100 kilograms body weight in the shorn animal and only 2 liters in the unshorn camel. Thus a shorn camel with fur 0.5-1 centimeters long would evaporate 50 percent more water than would an animal with unshorn fur. The temperature at the fur surface was as high as 70-80 C, so the temperature gradient through the fur was more than 30 C." Hilde Gauthier-Pilters and Anne Innis Dagg, The Camel, (Chicago: University of Chicago Press, 1981), p. 73

Think about the physics and you will see why fur hinders the efficiency of sweating.

1. Fur hinders the free flow of air. The air under the fur becomes saturated and must be replaced by dry air for heat to be removed.

2. Water on the skin under the fur is cooler than water would be on the open skin. Cooler temperature means slower evaporation and less heat removed per unit time.

3. Some of the sweat under the fur will be stuck to the hair itself. When it evaporates, it cools the hair, which does not have the same effect as cooling the skin, under which flows the blood. It is the blood which needs to be cooled so that it can cool the interior of the body.

One gentleman continues to claim that a furred camel is more efficient at sweating than is man.  I find this very odd so I am adding this to show how wrong this idea is. A furred animal which sweats 2 liters of water is less efficient than one which sweats 3 liters of water. Efficiency is a rate, quantity per hour per 100 kg. If the purpose is to examine heat removal, which is what we are talking about here, then the more water which can evaporate the more heat is removed in a shorter time. So, efficiency in heat removal is the system that removes more heat. Thus allowing 3 kg of water to evaporate in a given time is more efficient at heat removal than allowing only 2 kg of water to evaporate in the same time.

I sent this to that gentleman on  January 8, 1997.  FOR HEAT REMOVAL under hair being more efficient. The entire reason mankind lost his hair was because the brain required heat removal and it was slower and less efficient under fur as Gauthier-Pilters and  Dagg show.

The heat removed when a gram of water is evaporated is 600 calories. A liter is 1000 g. Thus 3 liters on the shorn camel removes 3000*600=1.8 million small calories, or in food calories terms, 1800 calories (these are the large calories) But 2 liters removes only 1200 large calories. The shorn camel is more efficient at heat removal. And until you can show that a furred camel sweats more than this, then you haven't shown that he is more efficient. The furred camel is more efficient AT WATER RETENTION BUT NOT HEAT REMOVAL.

Now, what if a camel actually sweated at a human rate. What would that mean? I checked the Grolier's encyclopedia for the following data. A camel can be as hefty as 680 kg and can lose 25% of his weight in water. So, a 600 kg camel if he sweated as much as a human would go through 48 liters/100 kg/day * 6= 288 liters of water per day. Since they can go without water for 7-9 days that means that their bodies must store 2592 liters of water. Thus the camel MUST then have a volume which is greater than 1000cc/liter X 2592 liters = 2592000 cc. And since water weighs 1 g/cc the camel must be a behemoth which weights 2592 kg. Of course the weight of a camel is usually no more than 700 kg. So, yes a camel sweats, but no where near as great as a man. Lets look at this another way. If a camel can only lose 25% of his weight in water, that is 170 kg of water. As we have seen,  if a camel sweated as severely as a human, then he would have to sweat more than that in a single day. Thus, if a camel sweats like a human, he can only go one day without water. QED.  Man's sweating rate is unique--I stand by this and any suggestion that our sweating is not unique among the mammals displays a lack of knowledge of the topic as well as a lack of actually doing the above calculations which would show how silly the idea is.

Campbell,Bernard, 1974. Human Evolution, (Chicago: Aldine Publishing).

Fagan,Brian M. 1990. The Journey From Eden, (London: Thames and Hudson)

Falk, Dean, 1992 Braindance,(New York: Henry Holt and Co.)

Johanson, Donald and James Shreeve, 1989, Lucy's Child, (New York: William Morrow).

Larick, Roy and Russell L. Ciochon, 1996, "The African Emergence and Early Asian Dispersals of the Genus Homo."American Scientists, 84(Nov/Dec, 1996).

Ruff, Christopher B., 1993, "Climatic Adaptation and Hominid Evolution: The Thermoregulatory Imperative," Evolutionary Anthropology, 2:2, p. 53-60,

Shipman, P. and A. Walker, 1989. "The Costs of Becoming a Predator," Journal of Human Evolution, 18, 373-392.

Stanley, Steven M., 1998, Children of the Ice Age, (New York: W. H. Freeman)

Walker, Alan and Pat Shipman, 1996, The Wisdom of the Bones, (New York: Alfred Knopf).

Zihlman, Adrienne L. and B. A. Cohn, 1986, "Responses of Hominid Skin to the Savanna," South African Journal of Science, 82:2, p. 307-308.

Zihlman, Adrienne L. and B. A. Cohn, 1988, "The Adaptive Response of Human Skin to the Savanna" Human Evolution, 3:5(1988):397-409.

Last Modified 8-22-98