flinn@seismo.UUCP (E. A. Flinn) (04/26/84)
There is an interesting article by Elaine Morgan on pages 11-13 of the April 12th 'New Scientist' about the hypothesis that there may have been an acquatic phase in human evolution. She notes Alister Hardy's suggestion in 1960 that such a phase could account for several characteristics that are unique to humans among the hominids, but common among acquatic mammals (lack of body hair, presence of subcutaneous fat, face-to-face copulation, the position of fetal hair, and weeping). It would also explain the pre-adaptations necessary for the emergence of bipedalism and speech. There was flooding in northeastern Africa during the "fossil gap" 4-8 million years ago, after which bipedal hominids first appeared; the flooding may have induced isolated populations of apes to adopt an aquatic style of life, and the subsiding waters would have forced these apes back to land. Another way that humans are unique among land mammals is in our sodium homeostasis: other mammals suffering from sodium deficiency have a compelling craving for salt, and once the deficiency is made up, the appetite vanishes sharply. This mechanism does not operate in humans, so that salt intake has little or no relation to the body's needs, varying from salt aversion in some peoples to excessive intake in western countries. High death rates from diarrhoeal infections have been reported in underdeveloped areas where salt is readily available and its ingestion would save lives, but the active craving triggered in other species by sodium deficit is not triggered. Alone among primates, humans cool their bodies by sweating, which is profligate of sodium as well as water. It's hard to escape the conclusion that one single species of ape in Africa revolutionized its management of both intake and excretion of salt; apparently it is difficult to explain this without humans having spent some of their evolution time in the sea. Marine birds, for example, allowed for excessive salt intake and evolved new ways to eliminate the surplus; humans are apparently the only land animals to have done the same. Humans can hold their breaths for long periods while diving; again, this is unique among land mammals. In humans, as in seals and ducks, vascular constriction during diving is not limited to the arterioles but extends to larger arteries also, which indicates specialized adaptation. Studies have shown that the human diving responses such as apnoea and bradycardia are not purely unconditioned reflexes, but are influenced by higher brain centers to the extent that they can develop in anticipation of immersion - dolphins also have this characteristic. Morgan notes that an incidental advantage arising from this characteristic is the acquisition of sophisticated volitional breath control, without which human speech was unlikely to have evolved. As to the nakedness of the naked ape, there are only two environments known to be conducive to hairlessness in mammals: aquatic and subterranean. Only one environment is known to be conducive to hairlessness plus the subcutaneous fat layer that characterizes humans (alone among primates): the acquatic. The Australopithecus afarensis skeleton shows that this ape was bipedal, and that the bipedalism was so far advanced that this must have evolved earlier, in the fossil gap. A. afarensis left no evidence that they were hunters, so the inference is that the bipedalism evolved for some purpose other than carrying weapons and hurling spears. While a chimpanzee's pelvis is narrow and long, Lucy's was wide and short (as in Homo sapiens), indicating long habituation to a mode of locomotion in which the spine and the hind limbs are roughly in the same plane, instead of at an angle of about 90o, as in most quadrupeds. This alignment is unknown in tree-dwelling primates. Swimming is the only known method of mammalian locomotion in which this pelvic orientation can evolve without necessitating simultaneous weight-bearing adaptations in the lower limbs. If Lucy's ancestors had been swimmers, their descendants returning to land would have had a pelvis powerfully pre-adapted to bipedalism, but their legs and feet would not yet have been fully adapted. This too is seen in the Lucy skeleton, since the toes are long, slender, and curved, the big toe is still slightly opposable, and the automatic locking mechanism of the knee was not yet perfected. Morgan discusses other points, and refers to her book, 'The Acquatic Ape,' published in 1982.
rej@cornell.UUCP (04/27/84)
The first place that I saw this idea (not that I am particularly expert in the area) was in "The Descent of Woman", by a feminist evolutionary biologist. It is a very interesting book, especially to those of us who are fascinated by the way idiology effects science.
dsf@allegra.UUCP (David Fox) (04/27/84)
R. Buckminster Fuller proposed this theory in his book "Critical Path," which was published around 1981. He argues that the assumption that the fossils we find in East(?) Africa represent earliest man is unfounded, since there might have been earlier humans whose remains have not been preserved by the fortuitous (sp?) geological circumstances which exist(ed) in Africa. I can't completely recall his arguments, but I do remember that he claims that humanity originated in the islands off southeast Asia. He mentions the antiquity of the shipbuilding industry, the sealevel during the interglacial period, migration patterns based on prevailing winds, raw materials, population densities, etc. etc. I found it very interesting. I also found it convincing, but I'm fairly credulous in matters I know little about. I'd be interested in hearing other people's reactions, but unfortunately I'm going "off-line" for an unknown period of time. Goodbye, Netland David Fox nowhere!nobody
matt@oddjob.UChicago.UUCP (Matt Crawford) (04/28/84)
Sometime in college I saw a graph of the transmission functions of air and water both compared to the sensitivity of the human eye, as a function of wavelength. The eye's response fit into a wide peak in air's transmission but was almost an exact match to water. I thought the graph I saw was in the Feynman Lectures on Physics, but I can't find it there now. Maybe somebody else has seen the like somewhere?
riddle@ut-sally.UUCP (Prentiss Riddle) (04/29/84)
If memory serves, Carl Sagan also mentioned some variant of this theory
in his book of nearly a decade back, "The Dragons of Eden". I'm sure
that he got the idea from some even earlier source. Check Sagan's book
for references.
He also cited a couple more purportedly aquatic features which we have
but the other primates lack: our downturned nostrils (quite an aid in
holding one's breath underwater) and the traces of webbing found
between our fingers and toes. If I recall Sagan's statement of the
theory correctly, the speculation is not that we were ever exclusively
aquatic like whales or porpoises, but that we evolved at water's edge,
spending considerable time both in and out of the water.
--- Prentiss Riddle ("Aprendiz de todo, maestro de nada.")
--- {ihnp4,seismo,gatech,ctvax}!ut-sally!riddlenonh@utzoo.UUCP (Chris Robertson) (04/30/84)
By a strange coincidence, "The Descent of Woman" just happens to have been written by Elaine Morgan...
dan@gargoyle.UChicago.UUCP (Dan Breslau) (05/02/84)
Isn't there a rare recessive gene for webbed fingers and toes? Dan Breslau ...ihnp4!crsp!gargoyle!dan
kissell@flairvax.UUCP (Kevin Kissell) (05/22/84)
(ahem)
Another (somewhat apocryphal) data point on the subject is the observation
I recall reading that the hairs on the human torso tend naturally to lie
along the path of water-flow around a swimming body.
Kevin D. Kissell
uucp: {ihnp4 decvax}!decwrl!\
>flairvax!kissell
{ucbvax sdcrdcf}!hplabs!/rbg@cbosgd.UUCP (Richard Goldschmidt) (05/22/84)
Another of the interesting points brought up by Elaine Morgan in her book, The Descent of Woman, was the shape of the human nose. It is very different than the forward-directed nostrils of most primates. Presumably, all the better to trap air rather than flooding your nose in an aquatic environment.