barger@ils.nwu.edu (Jorn Barger) (11/03/90)
In article <1371@cluster.cs.su.oz.au> louie@cluster.cs.su.oz.au (Luis Esteban) writes: > I have received a number of solutions to why we have > eyebrows. I have some questions concerning them. > The following is a composition of the explanations and questions. [stuff deleted] I've been waiting for years for someone to ask me this (why do humans have eyebrows). It seems transparently obvious to me that they are primarily _signal-flags_, bars of contrasting color that amplify our emotional expressions, making them readable more easily at a greater distance. Why did humans lose their fur? This seems surely due to sexual selection, not natural selection. But why this baldness became sexually attractive I have no clue. In general, sexual selection is not considered often enough as an evolutionary force. I think that the punctuated equilibrium paradox makes perfect sense if viewed as a case of sexual selection overpowering natural selection until the environmental stresses finally become too great. ................................................................... "The man who pretends to be a modest enquirer into the truth of a self-evident thing is a knave." William Blake ...................................................................
teexmmo@ioe.lon.ac.uk (Matthew Moore) (11/05/90)
Jorn Barger > writes: > >I've been waiting for years for someone to ask me this (why do humans have >eyebrows). It seems transparently obvious to me that they are primarily >_signal-flags_, bars of contrasting color that amplify our emotional >expressions, making them readable more easily at a greater distance. > >Why did humans lose their fur? This seems surely due to sexual selection, >not natural selection. But why this baldness became sexually attractive I >have no clue. > It may be "transparently obvious" to you, but this does not make it the only explanation in the literature. The Hardy-Morgan theory of human evolution (aka the aquatic theory) considers eyebrows to be sunshades. What do you do if the sun gets in your eyes? - You frown, or lower your eyebrows. Loss of fur is a common adaptation to aquatic life (or semi aquatic life), consider the elephant, pig, hippoo, cetaceans (whales and dolphins). Indeed, Hardy first formed his theory when, on his return from a whaling trip, he was struck by the similarity between whale blubber and the human layer of subcutaneous fat. (Subcutaeneous fat being an aquatic adaptation against heat loss).
kell@cs.albany.edu (Brian A. Kell) (11/06/90)
In article <1990Nov5.123912.15186@ioe.lon.ac.uk>, teexmmo@ioe.lon.ac.uk (Matthew Moore) writes: > The Hardy-Morgan theory of human evolution (aka the aquatic theory) > considers eyebrows to be sunshades. What do you do if the sun gets in > your eyes? - You frown, or lower your eyebrows. ... and maybe shade your eyes with your hand? My theory (although I'm no expert!) has always been that eyebrows make really good rain gutters. If you ever stand/walk/hike/jog/etc. in the rain, you may notice that the raindrops hitting your forehead are neatly diverted to the side by your eyebrows, allowing clearer vision than if the water were dribbling into your eyes. This seems to have an obvious selective advantage for hunting and/or evading predators in the days before umbrellas and windshield wipers. ---------------------------------------------------------------------------- Brian Kell SUNY/Albany Departments of Computer Science and Biological Sciences brian@isadora.albany.edu kell@cs.albany.edu bk7295@albnyvms.bitnet
sarima@tdatirv.UUCP (Stanley Friesen) (11/08/90)
In article <1990Nov5.123912.15186@ioe.lon.ac.uk> teexmmo@ioe.lon.ac.uk (Matthew Moore) writes: >The Hardy-Morgan theory of human evolution (aka the aquatic theory) >Loss of fur is a common adaptation to aquatic life (or semi aquatic >life), consider the elephant, pig, hippoo, cetaceans (whales and dolphins). Except that of these examples only the hippos and cetaceans are (semi-)aquatic. Elephants and pigs are as terrestrial as any mammal (that is *all* mammals spend *some* time in/around water). There is another set of circumstances that is leads to loss of hair - namely large size in a relatively equable climate. The examples include: elephant, rhinoceros, &c. Since humans are among the top 10% of the mammals as far as size is concerned, and since we apparently evolved in the tropics, our hairless state could well be due to that. As far as the eyebrows are concerned, the idea about sun visors may well be correct - the bright, steady sun is a major problem in the tropics. -- --------------- uunet!tdatirv!sarima (Stanley Friesen)
msissom@digi.lonestar.org (Marc Sissom) (11/10/90)
> >Loss of fur is a common adaptation to aquatic life (or semi aquatic >life), consider the elephant, pig, hippoo, cetaceans (whales and dolphins). >Indeed, Hardy first formed his theory when, on his return from a >whaling trip, he was struck by the similarity between whale blubber >and the human layer of subcutaneous fat. >(Subcutaeneous fat being an aquatic adaptation against heat loss). Some more support for this 'aquatic period' of human development is the fact that while all other primates are almost completely furred; humans are the inverse, almost completely 'fur-less'. The complement to this is that no other primates(as far as I know) have any background, or history of an aquatic or amphibious lifestyle. Nor do they have any affinity for activity in the water which humans certainly do. Also none exibits this subcutaneous layer of fat. On the other side, is the evidence that no other primates are bipedal, nor do they have any features to implement or enhance the development of aerobic stamina. This supports the argument that the relatively hairless skin with perspiration and cappillary dialation can be a very effective radiator for a body that is running around Africa all day. A breeze across the skin greatly enhances the value of perspiration - the draft caused by walking/running or by the wind. However, with the loss of the insulating cover of fir, the skin(even with the blood flow restricted) can now be a tremendous drain on the body heat in other relatively cool climates. The fat layer can make up somewhat for this loss of an insulating layer in cool conditions. Note that the fat does not cut off the emission of heat when the body is hot because the cappillaries are on the outside of the fat layer and provide a channel for the flow of the excess heat.