Tears

Update note: some proponents of the AAT/H have moved away from the idea that the aquatic phase was in a salt water environment, but most still claim humans' sweat and tears systems evolved as an aquatic feature, as an excretory system for salt. This is a remarkable development, and demonstrates one of the reasons the AAT isn't taken seriously by those who study the evidence. If tears and sweat in humans are claimed to be due to an aquatic lifestyle and the need to excrete salt, the aquatic lifestyle must have been in a salt water environment. A freshwater aquatic period would be no more or less likely to produce these adaptations than a terrestrial lifestyle, so the purported aquatic lifestyle doesn't explain the supposed adaptation of sweat and tears as systems to excrete salt. Of course the AAT/H proponents are wrong about what the human sweat and tears systems can do, so that just compounds their error.

Tears and the AAT/H

"Until evidence of other animals shedding emotional tears is well documented, I will continue to maintain that emotional tearing generally occurs only in humans. I agree with Montagu's view that 'the shedding of tears as an accompaniment to emotional distress has been attributed to other animals... The truth, however, appears to be that while some of these animals may on occasion exhibit the evidences of tears, this occurs very seldom, and is the exception rather than the rule. ...Psychic weeping is not known to occur as a normal function in any animal other than man.'" (William H. Frey 1985: 147. Crying: The Mystery of Tears by William H. Frey, Ph.D. with Muriel Langseth. Minneapolis: Winston Press.)

Some of you may recognize the name of the quoted above; he's the guy Elaine Morgan correctly refers to as "a leading present-day authority on the subject" (Morgan 1990: 98, The Scars of Evolution). Dr. Frey has done studies of emotional tears and Morgan feels they support her theory. Why she feels they support her is rather inexplicable, once you look at the evidence, including the evidence in the book which Morgan cites.

This particular AAT/H idea, initially promoted by Morgan and since repeated many times by AAT/H proponents, is that emotional tears are seen only in humans and aquatic animals (she cites Frey as proof despite his conclusion, which I quoted just now) and they (and our sweat glands) evolved as system to excrete salt. To do this, she ignores a basic principle of physiology I've described below in a section on homeostasis.

This section is in two parts: this first part is specifically on evidence for emotional tears in non-human animals. The second deals with tears and what they contain, and what this means in regard to the likelihood of tears being an excretion system.

Do Animals Shed Emotional Tears?

This is the title of chapter 14 in William Frey's book (Morgan cited it in The Scars of Evolution but left off the main title, leaving only the sub-title, and also left off Frey's co-writer). In it Frey looks at evidence, both scientific and anecdotal, for emotional tearing in non-human animals. His conclusion opened this page.

From Frey's Chapter 14: Do Animals Shed Emotional Tears?

from pp. 135-139: "Some Scientists Say Animals Cry Tears"

In this section Frey mentions "several reports of animals shedding emotional tears -- or what were interpreted as emotional tears -- in the scientific literature cannot be ignored."

Frey opens with Darwin's reports of tears in Indian elephants. Frey also points out the information that AAT/H proponents never seem to mention (even though it appears on the same page of Darwin's Expression of the Emotions in Man and Animals); that Darwin reported contrary information from his correspondents in Ceylon, where observations of recently captured elephants showed no tearing, and "the native hunters asserted they had never observed elephants weeping".

Then Frey continues with reports of other animals shedding tears: dogs and wolves (Cecil Reynolds 1925); seal (Ronald M. Lockley 1966 Grey Seal, Common Seal); sea otter (Georg W. Stellar); lab rats (red tears from Harderian glands [the same types of glands that elephants have]) (John E. Harkness and Marcella D. Ridgeway); and gorilla (Dian Fossey 1983 Gorillas in the Mist).

Note that already we see a mix of aquatic and non-aquatic animals mentioned; this will be a repeating theme, as you'll see. Another recurring theme, and the reason Frey ultimately does not accept these reports as documented, is that none of these reports, indeed none of the "pro-tears" reports, have any means of determining that these tears are due to emotion rather than stress or irritation. In any event, this already destroys the AAT/H claim that only aquatic animals have been reported shedding emotional tears. It should also be noted that Frey's book was cited by Morgan, who nevertheless somehow managed to skip all the reports of non-aquatic animals, despite the fact that they are interspersed with the reports of tears in aquatic animals, just as they are in my list in the paragraph above.

from pp. 139-141: "What Animal Experts Say"

In this section, Frey and his co-writer sent out questionnaires to zoos, animal parks, and marine parks, veterinarians, etc., to see if any of them reported ever seeing emotional tears in nonhuman animals.

Brian Davies, "an animal protectionist and executive director of the International Fund for Animal Welfare" (he's written two books protesting the harp seal hunts in Canada) says yes for seals. Wayne Franzen, trainer of Okha (an Indian elephant), and co-owner of Franzen Brothers Circus, says yes for Indian elephant.

Ian Douglas-Hamilton, "who has done extensive studies of African elephants replied, 'I cannot say that I observed emotional tears in African elephants, although I have seen tears appear when they have been shot or wounded. It is possible that these may be related to emotion, but I am sorry to say I really do not have enough observation in this to say one way or the other'."

Frederick A. King, director of Yerkes Primate Center in Atlanta and survey of 5 experienced primate scientists there say no.

The following experts were asked "(1) Have you ever seen nonhuman animals shed emotional tears? and (2) Do you know of any documented evidence of nonhuman animals shedding emotional tears?" Saul Kitchener, director of the San Francisco Zoological Park; R.M. McNorman, assistant curator of mammals, Bronx Zoo; G. Styfer, overseer at the Toronto Zoological Park; Donald L. Jansen, DVM, associate veterinarian at the San Diego Wild Animal Park; Sanford Friedman, curator and chairman of mammal department at the Brookfield Zoological Park in Illinois "all responded no to both questions".

"Veterinarians and animal trainers who have worked extensively with seals, dolphins, and whales at Sea World in Orlando, Florida, the Seaquarium in Miami, Florida, Marineland in Los Angeles, California, and the Como Park Zoo in St. Paul, Minnesota" all said no. As they report, "seals, dolphins, and whales secrete a watery mucus to protect their eyes from sea water. The overflow of tears due to lack of a drainage system may have been misconstrued as emotional tears".

from pp. 141-146: "Other Reports of Animals' Tears"
Finally, since his earlier work was written about in Psychology Today, Frey has gotten many anecdotal reports about pets or other animals shedding tears. These animals include dogs, cats, cows, pigs, lambs, horse, and a kangaroo.

Summary:

So we can see that there is every bit as much, and as little, evidence for non-aquatic animals shedding emotional tears as there is for aquatic animals. This is contrary to Morgan's claims in print, as well as the claims Morgan and others have made repeatedly in the sci.anthropology.paleo newsgroup and other online forums.

We also see still more evidence of Morgan's style, deliberately burying contrary evidence that is in a book which she cites. (Unless we are to believe that when she read Frey's book, she didn't read the chapter entitled "Do Animals Shed Emotional Tears?" -- does anyone believe that's likely?)

This second part deals with tears and what they contain, and what this means in regard to the likelihood of tears being an excretion system.

When Morgan cites William Frey's work as support for the AAT/H; her reasoning is twofold:

1. She claims that emotional tears are shed by humans, aquatic animals, and Indian elephants, and by no other animals. Part one of my post showed that the evidence for this does not exist. There are no documented cases of emotional tears being shed by any nonhuman animal, and though there are anecdotal reports of such tears in nonhuman animals, these report such tears in many non-aquatic animals. So it cannot be said to be a trait shared only by humans, aquatic animals, and Indian elephants.

2. Frey's work demonstrates that emotional tears do serve an excretory function, and Morgan claims that the original function of emotional tears was the elimination of salt.

First we have an interesting point; then we have to clear up some confusion introduced by Morgan's inaccurate terminology.

The point is that the composition of human tears does show an excretory function of tears which sheds light on their environment of origin. This feature of tears, that they are excretory in regard to some elements, was known even before Frey's work. The actual composition of tears, as opposed to some imagined or postulated composition, is not favorable to the AAT/H, but we'll come to that at the end.

The problem is the confusion Morgan has introduced regarding the types of tears. She uses the term "psychic tears", and posits these as being one of two types of tears, the other being "reflex". She claims there is "general agreement on this", but in fact she is confused. The two types of tears are "basic" (now generally called "basal" or "continuous" tears) and "reflex" tears, and there is in fact general agreement on this. Emotional, also called "psychogenic", tears are one form of reflex tears. The stimulus is emotional rather than being irritant-induced. Basal tears are the normal tear contribution to the "tear film" which lubricates the eye.

"Reflex secretion may be of peripheral sensory origin through fifth nerve stimulation (cornea, conjunctiva, skin, nose) or of central sensory origin. In the latter the stimulation may be retinal, varying with the intensity of light, or psychogenic, as in weeping caused by emotional disturbances or by various central nervous system diseases. The production of tears on an emotional basis is unique to humans among all vertebrates". (Benjamin Milder 1987:24)

The excretory abilities of the lacrimal (tear) glands

It is an established physiological fact that to be involved in changing the body's balance of a substance, such as salt (the balance in what we are talking about is the balance of water to a given substance), any given excretion must contain a concentration of the substance that is greater than its concentration in plasma, which is called being "hypertonic". An organ which does this is said to be capable of "active" rather than "passive" excretion for that substance. That the lacrimal glands can and do perform active excretion is well known to those in the field of ophthalmology. However, they are not capable of actively excreting sodium, as the AAT/H requires.

Central to Morgan's thesis is that our lacrimal glands actively excreted salt at some time in the past, even though they don't now. This requires that our lacrimal glands underwent two massive changes, starting and ending with a passive secretion of sodium. This idea is certainly far less parsimonious than the idea that the observed and measured active secretion of the lacrimal gland indicates our actual environmental past habitat.

Secretions in tears

The facts on substances which the lacrimal gland is capable of actively excreting, and on sodium, which the lacrimal gland cannot concentrate sufficiently for active excretion.

"Sodium in tears is about equal to that in plasma and has been found to correlate with it, suggesting a passive secretion into the tears.

"Potassium, with an average value of about 20 mmol/l is much higher than the corresponding plasma concentration of about 5 mmol/l. This indicates an active secretion into the tears". (van Haeringen 1981:92)

"The manganese concentration of emotional tears (25.2 +/- 6.6 ng/ml) was not significantly different from that of irritant-induced tears (34.2 +/- 8.8 ng/ml) obtained from the same healthy female subjects". (Frey et al. 1981:564)

"The manganese concentration of emotional tears from women exceeded that of serum (0.98 +/- 0.09 ng/ml) obtained from the same subjects by about 30-fold". (Frey et al. 1981:564)

"Paired samples from 25 women also showed that the protein concentration of emotional tears was 24% greater than that of irritant-induced tears (P<.01) (Table 1). We found a higher protein concentration for emotional tears from men as well (P>.05), although we obtained paired samples from only four subjects". (Frey et al. 1981:562)

The only higher concentrations that Frey and his colleagues found being excreted in emotional tears as contrasted to irritant-induced tears were higher concentrations of proteins. Frey feels that the process of crying helps in emotional release through eliminating substances such as prolactin, ACTH, Leucine-Enkephalin, and manganese. He also feels that the levels of prolactin in one's system provide a threshold effect, affecting how easily emotional tears are shed in response to a given stimulus. This, he thinks, accounts for his findings that women "shed tears more often and more readily than men". Adult women typically have much higher levels of prolactin than adult males, and these levels also rise during pregnancy, another period when emotional tears are known to be more easily shed.

Innervation of tear secretion

Morgan has suggested that the source of control for psychogenic tearing is important to her theory, but this is based on her mistaken idea that human emotional tearing is a characteristic shared by aquatic animals and no other animals. This has been shown to be a completely unsupported notion: there is no documented evidence for nonhuman aquatic animals shedding emotional tears, and the anecdotal and non-documented evidence is at least as strong or stronger for emotional tears in non-aquatic nonhuman animals.

What matters is the ability of lacrimal glands to excrete hypertonic substances. If they cannot excrete a given substance with a greater concentration than it appears in plasma (i.e., "hypertonic"), the purpose for these tears cannot be for excretion of an excess of that substance. It is well documented that human tears are never hypertonic in regard to sodium.

Tears are, however, strongly hypertonic in regard to potassium. In this regard, the lacrimal glands call to mind the "salt" glands of terrestrial reptiles and birds. Morgan has many times -- both in published work and online -- inaccurately claimed that salt glands are only found in marine birds and reptiles, ignoring the many terrestrial birds and reptiles who have these glands. These animals include ostriches and other birds, and lizards, including iguanas, chuckwallas, and others. The "salt" glands of these terrestrial birds and reptiles, unlike those found in marine birds and reptiles, are used primarily to excrete potassium. "In other words the secretion resembles that of the ostrich and differs markedly in composition from that of marine birds and reptiles" (Peaker and Linzell 1975:247-8).

So the actual observed and measured excretions in human tears far more closely resemble the excretions from the "salt" glands of terrestrial birds and reptiles than those of marine birds and reptiles. Thus for human tears' excretory abilities to indicate a terrestrial background requires no change. For their abilities to indicate a marine background requires not just one but two massive changes, starting and ending with a passive secretion of sodium.

The idea that human tears indicate a marine past is certainly far less parsimonious than the idea that the actual observed and measured active secretion of the lacrimal gland indicates our actual environmental past habitat would be terrestrial rather than aquatic.

References

1975 Salt Glands in Birds and Reptiles by M. Peaker and J.L. Linzell (Dept. of Physiology, Agricultural Research Council, Institute of Animal Physiology, Babraham, Cambridge). Monographs of the Physiological Society No. 32. Cambridge University Press: Cambridge, London, New York, Melbourne.

1981 "Clinical Biochemistry of Tears" by N.J. van Haeringen, Ph.D. Survey of Ophthalmology 26(2):84-96.

1981 "Effect of stimulus on the chemical composition of human tears" by William H. Frey II, Ph.D., Denise DeSota-Johnson, B.A., and Carrie Hoffman, B.S.; and John T. McCall, Ph.D. American Journal of Ophthalmology 92:559-567.

1985 Crying: The Mystery of Tears by William H. Frey II, Ph.D. with Muriel Langseth. Minneapolis: Winston Press.

1987 "Chapter 2: The lacrimal apparatus" by Benjamin Milder, M.D. In Adler's Physiology of the Eye: Clinical Application, edited by Robert A. Moses, M.D. and William M. Hart, Jr., M.D., Ph.D. Eighth edition. The C.V. Mosby Company: St. Louis, Washington, D.C., and Toronto.

Homeostasis

Homeostasis in bodily fluids refers to a self-regulating process wherein an organism maintains, within reasonable limits, a relatively steady balance of a given substance. One of the most important of these is salt. Our plasma contains salt, and we need a certain amount of it or we get sick or die. This is not just true of blood plasma, but the fluid (cytoplasm) in all our cells. This isn't due to aquatic or non-aquatic lifestyles, it's common to all vertebrates. (Its only connection to aquaticness is that it's almost certainly a holdover from the extremely ancient past of hundreds of million of years ago when there actually were nothing but aquatic animals.) If we get too much salt in those fluids, we have to be able to get rid of some or we get sick or die. This also is true of all vertebrates, terrestrial and aquatic. Homeostasis in bodily fluids doesn't just pertain to salt and water; other elements, like potassium, are involved too. The AAT/H often focuses on this process because how these systems work in different animals does say a lot about the environmental backgrounds over their evolutionary history. They are right to look at it, but sadly, they generally seem to lack a basic understanding of the physiology behind it, which leads them to make huge errors. Our method of maintaining balance in both salt and potassium, when compared to aquatic and terrestrial mammals, does indeed point to one of the two environments as the one we evolved in. But it isn't aquatic.

It is an established physiological fact that to be involved in changing the body's balance of a substance, such as salt or potassium (the balance in what we are talking about is the balance of water to a given substance), any given excretion must contain a concentration of the substance that is greater than its concentration in plasma, which is called being "hypertonic". An organ which does this is said to be capable of "active" rather than "passive" excretion for that substance. For example, while AAT/H proponents claim we used our sweat glands and tears to excrete salt, they are not capable, or even close to being capable, of active secretion. This is true of all mammals, including aquatic mammals. Only one organ in mammals is capable of actively excreting salt, the kidneys. This is why the kidneys of marine mammals are all large and heavily lobed, unlike human kidneys; with better hormonal control over rate of urine formation and concentration via the kidneys. Besides the aquatic marine environment, there is one other environment which needs this type of adaptation, and that, ironically, is very dry deserts. The problem in both places is the same, little or no fresh water, and the denizens thereof must be able to conserve the water they get and expel the salt they get with it. So kangaroo rats and whales turn out to have a lot in common, homeostasis-wise. Note that when I pointed this out in the sci.anthropology.paleo newsgroup, some AAT/H proponents (including Elaine Morgan) couldn't see why we would use the same system that every other mammal uses, without exception.

Because birds' and reptiles' kidneys are not as highly developed as those of mammals, they have had to develop the salt glands that AAT/H proponents think we should've emulated. Remember that an organism can't just evolve whatever feature it likes, like picking up a performance muffler and installing it on your car. They start with what they have, and birds and reptiles have kidneys which are inefficient compared to those of mammals. In fact, the more sophisticated kidney is considered to be one of the great mammalian adaptations. All mammals faced with high salt loads relative to fresh water availability, have developed specialized kidneys to deal with the problem, kidneys which can produce highly concentrated urine. Humans do not have these features. Aquatic mammals, in fact, can even get necessary water by drinking seawater for an indefinite period; humans doing so get sick and die. (Aquatic mammals actually generally get enough water through their food, which is also about as salty as seawater.)

Besides the simple yet critical matter of sweating being entirely incapable of producing the required hypertonic salt-water mix -- it's never even close to hypertonic -- there is another critical reason that sweating (whether eccrine or apocrine) is not a usable salt excretion system: its essentially unregulated nature (the mammalian renal system, on the other hand, is a highly regulated system whose purpose is the regulated excretion of various substances and the maintenance of the required salt-water balance). If you simply sweat a lot and drink fresh water, under work stress the renal system can shut down. This causes a health crisis, with accompanying violent and painful cramps, as well as -- less immediately dangerous but still critical -- fatigue and depression. This would make relying on "sweating plus drinking water" a highly dangerous form of salt excretion, even if the required large amounts of drinking water are available.

How large would these amounts of water be? Assume for a moment that you don't mind violent cramps on a daily basis, and that they wouldn't be a problem for an aquatic mammal. How much would you have to sweat to sweat out this salt? Some early researchers had the idea that sweat might be a excretory process rather than the one which tends to retain as much non-water as possible. They of course realized that salt was far too dilute in sweat for it to be a target of this hypothesized excretory system; they went for urea as the target. However, researchers J.S. Weiner and K. Hellman pointed out that the sweat glands' activity "is directed quite to the opposite purpose, of conserving sodium chloride and glucose" (1960:171) and they did the calculations to see how much sweat would be required to perform this task: the number is 80 liters. 80 liters of sweat every day, and the upper limit for men working all day in desert conditions (far more strenuous and harsh conditions than our hominid ancestors would go through) is 10 liters (6 liters being the more normal amount under those harsh conditions). Clearly, sweat just can't be expected to do the job, and keep in mind that urea is far more plentiful in sweat than salt is. And even if you could sweat more than 80 liters a day, every day, there's those violent cramps. Sweat as an excretory system just doesn't make sense at all. By the way, all this info was available long before even Hardy wrote up his AAT/H paper; even longer before Morgan did her first book on the subject. Was Morgan aware of it? I got the reference to Weiner and Hellman's research from her; she quoted them. So she had the info in her hand that proved her contention to be wrong even as she wrote it up.

Organisms which rely on maintaining a salt-water balance (all vertebrates except for some fish) must have a regulated system which doesn't simply "mess up" their salt-water balance. This isn't just a nicety, or a handy option in life; it's a critically important need without which the organism cannot live. Amongst mammals this system is always, without exception, the renal system; it is never, ever, any other system... period. Other types of vertebrates utilize other systems -- gills, salt glands, or the skin itself -- but mammals always use the kidneys. Period.

This is not opinion or hypothesis, but basic physiological fact.

1988 Animal Physiology: Mechanisms and Adaptations (3rd edition) by Roger Eckert (University of California, Los Angeles), with Chapters 13 and 14 by David Randall (University of British Columbia), revised in part by George Augustine (University of Southern California). W.H. Freeman and Company: New York.

pg. 393:

The Vertebrate Kidney
To speak of the vertebrate kidney would be misleading unless we note that it is organized somewhat differently in different groups of vertebrates. Comparisons can be made after we first consider the mammalian kidney. The mammalian kidney performs certain functions that in lower vertebrates are shared by such organs as the skin and bladder of amphibians, the gills of fishes, and the salt glands of birds and reptiles. It is also the osmoregulatory organ of which we have the most complete understanding, thanks to extensive research over the past four to five decades.

pg. 415:

Salt glands have subsequently been described in many species of birds and reptiles, especially those subjected to the osmotic stress of a marine or desert environment. These species include nearly all marine birds, ostriches, the marine iguana, sea snakes, and marine turtles, as well as many terrestrial reptiles. Crocodilians have a similar salt-secreting gland in the tongue.

pg. 415:

The formation of nasal gland fluid does not include filtration, as does the formation of urine by the glomerular kidney.

1978 Comparative Anatomy of the Vertebrates (4th edition) by George C. Kent (Department of Zoology and Physiology, Louisiana State University, Baton Rouge, Louisiana). C.V. Mosby Co.: Saint Louis.

pg. 326:

Sweat glands eliminate some salt in mammals, but salt loss by this route is merely incidental to secretion of water for its evaporative cooling effect. It is not a regulated route for salt excretion and, in fact, salt lost by this route usually must be replaced. Mammals eliminate excess salt via kidney tubules.

1990 Sea Otters by Marianne Riedmann. Monterey Bay Aquarium: Monterey, California

pg. 35:

Otters and most other marine mammals are constantly in danger of losing water to the more concentrated, or salty, ocean in which they live. They must keep the osmotic concentration of their body fluids constant despite their saltwater environment, a process known as osmoregulation. And besides living in sea water, sea otters eat marine invertebrates that have an elevated salt content, much higher than that of fishes, and often as high as that of the surrounding sea water. This salty diet raises the otter's "salt load" even further. Sea otters conserve water and maintain a suitable water balance by means of their large, heavily lobulated kidneys. Their kidneys are very efficient at concentrating urine by absorbing water and eliminating excess salt in urea, a waste product that's more concentrated than ocean water. Yet exhibit otters living at the aquarium sometimes drink fresh water from a hose and sprinklers that clean the windows. Although wild otters lack sources of fresh water, they do drink sea water, which may help them process and eliminate urea.

1990 The Pinnipeds: Seals, Sea Lions, and Walruses by Marianne Riedmann. University of California Press: Berkeley, L.A., and Oxford.

pg. 31:

Pinnipeds conserve water and maintain water balance in several ways. The heavily lobulated kidneys of seals and most marine mammals are extremely efficient at concentrating urine; they absorb water and eliminate excess salt in urine that has a concentration equal to or greater than seawater [various refs that I didn't copy]. The chloride concentration in seal urine is therefore as high as or higher than that of ocean water (which contains an average of 535 millimoles of chloride per liter). A seal that drinks a liter of seawater, after excreting the salts, ends up with a slight net gain of pure water. A human, however, experiences a net water loss of about a third of a liter of water after drinking the same amount of seawater. Human kidneys are less powerful than those of seals or whales, and even the most concentrated urine they can produce is always more dilute than salt water. Water is therefore wasted in eliminating the excess salt in urine.

1984 Grzimek's Animal Life Encyclopedia vol 11: Mammal II Dr. Bernhard Grzimek, ed. Van Nostrand Reinhold: New York, Cincinnati, Toronto, London, Melbourne

"Whales" by Dr. Everhard J. Slijper (Professor, Zoological Laboratory, University of Amsterdam) and Dr. Dietrich Heinemann (Director, Zoological Garden, Munster)

pg. 462, 467 (pages 463-466 are plates):

Vertebrate animals are not really built for an aquatic life; the salt content of their blood and body tissues is less than that of sea water. Thus the excess salt which is accumulated from food and water must be eliminated from the body. Whales do not have salt excretory cells like those the bone fishes have on their gills. They are not able to excrete salt through their nasal glands like many sea birds. Whales also do not have perspiration glands, which help many other mammals give off excess salt. The kidneys are the whale's only salt-excreting organs. Whales have very large kidneys relative to those of land mammals; the kidneys of small whales are twice as large as those in land mammals of the same size. In addition, the whale's kidneys are divided into several lobes, the renculi, so that the important exterior surface is increased. Whales are probably able to excrete large quantities of urine with their kidneys. We do know that the urine of the bottle-nosed dolphin occasionally contains particularly large amounts of salt.