Re: AAT Questions...sweat
Phil Nicholls (pnich@globalone.net)
Mon, 10 Jul 1995 21:15:47 GMT
When primates do sweat it is exclusively eccrine sweat. I posted the
following article about six months ago but it appears Pat et. al. have
forgotten it.
PRIMATE SWEATING
". . . the chief mystery does not lie in any one of these
ANOMALIES [emphasis added], not even the woderful brain or the
dexterous hands or the miracle of speech. It lies in the
sheer number and variety of the ways in which we differ from
out closest relatives in the animal kingdom." (Morgan, 1990)
Pat Dooley has once again raised the issue of the uniqueness of human
sweating, rejecting observations by noted primatologists that primates
sweat and if that sweat is a product of apocrine or errcrine glands.
Is human sweating really anomalous?
As Pat points out there are two main kinds of sweat glands in mammals.
Basically Eccrine glands are associated with hair follicles while
apocrine
glands open directly onto the skin. There are other differences as
well.
If we look at primates as a whole, we find that in Prosimians and
New World monkeys the apocrine glands are more numerous but that
in Old World Monkeys there distribution is at a ratio of 1:1, 1:2 or
1:3
depending on the body region sampled (Sokolov, 1982:160-169). For
the rhesus monkeys, Sokolov remarks that "Except for the lips and
ischila
callosities the eccrine glands are plentiful." (Sokolov, 1982,
p.165. Johnson and Elozondo (1974) note that the distribution of
eccrine
glands in the rhesus monkey is identical to that observed in humans.
For the chimpanzee, the Sokolov notes "All of the features of
chimpanzee eccrine glands are similar to those of humans. In
the immature female the apocrine sweat glands are much smaller
in size than in the male. These are fewer in number than the
eccrine glands." (Sokolov, 1982, p.169).
In primates ANY SWEATING THAT OCCURS IS ECCRINE SWEAT
(see Robertshaw, 1985 for an overview of sweating in primates
vs non-primates. For a look at the research on sweating in
primates, see Hiley, 1976; Johnson and Elizondo, 1974 and
Newman et. al., 1970). The first primates were probably
nocturnal, as are many of the living prosimians today. Nocturnal
primates do not really need to worry about overheating.
They discharge excess body heat by panting. As a result,
the apocrine glands in Prosimians did not develop a thermo-
regulatory role. As primates evolved and anthropoids appeared
and moved into diurnal niches, they continued to pant until two
evolutionary pressures forced a change. Increase in body size and
increase
in relative brain size are well known trends in anthropoid
evolution. As body size increases the number of eccrine sweat
glands also seems to increase (Robertshaw, 1985). As brain
size increases, the size of the nasal sinuses is reduced.
Since in closed-mouth panters this is the place where most of
the heat exchange takes place, the increase in brain size
produced a need for an alternative heat rejection system.
Now the question, as Pat asks, is why eccrine glands when
apocrine glands are the gland of choice in other mammals. The
answer, I believe, lies in the neurophysiology of sweating.
Apocrine glands are controlled by the sympathetic nervous
system. The neurons which control apocrine glands use
noradrenline as their neurotransmitter. Eccrine glands are
also controled by the sympathetic nervous system but unlike
apocrine glands they are cholinergic, i.e. use acetylcholine
as a neurotransmitter. The difference may be compared to
playing a piano. Noradrenline works like the pedals,
affecting the action of all the tones being played.
Acetylcholine is like the individual piano keys. Cholinergic
neurons are employed where fine control over the effector
organs is required. Anthropoid primates need a greater degree
of control over their heat rejection systems because of their
larger brains, which are very sensative to temperature
changes.
This is particularly important in Homo sapiens.
Apocrine sweat occurs in bursts which saturate the skin
quickly. The amount of sweat they produce cannot be regulated
nor can their action be sustained for any period of time.
(Robertshaw, 1985). This is ideal for an animal that needs to
cool off quickly after a period of brief intense activity but
are not suited to the task of regulating body temperature over
an extended period of time.
Eccrine sweating is not anomalous. It is consistant with the trend
observed in anthropoids, established long before the the
hominid/pongid split. Apocrine sweat glands never developed a
thermoregulatory role in primates. Eccrine sweating makes makes
good sense of neurophysiological grounds.
-------------------------------
Bligh, J (1967) A thesis concerning the process of secretion
and discharge of sweat. Environmental Search 1:28-51.
Hiley DA (1976) The thermoregulatory responses of the galago
(Galago crassicaudatus), the baboon (Papio cynocephalus) and
the chimpanzee (Pan satyrus) to heat stress. Journal of
Physiology, 254:657-670.
Johnson, GS and Elizondo, R (1974) Eccrine sweat gland in
Macaca mulatta: physiology, histochemistry and distribution.
Journal of Applied Physiology 37:814-820
Morgan, E. (1990) Scars of Evolution. New York: Oxford
University Press.
Newman, CM; Cummings, EG; Miller; Wright, H (1970)
Thermoregulatory responses of the baboon to heat stress and
scopolamine. Physiologists 13:271-285.
Robertshaw, D (1985) Sweat and heat exchange in man and other
mammals. Journal of Human Evolution 14: 63-73.
Sokolov, VE (1982) Mammal Skin. Berkeley, CA: University of
California Press.
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Phil Nicholls "To ask a question you must first
pnich@globalone.net know most of the answer.
Semper Alouatta! - Robert Sheckley
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