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Re: Hominid Altitudinal-Latitudinal Adaptations
(no name) ((no email))
20 Oct 1996 13:36:55 -0700
In article <01bbbe9f$a94a0aa0$5c2770c2@default>, "John says...
>
>It might be thought that terrestrial mammal specie needing to
>adapt from an equatorial climatic zone at sea level to a higher
>latitude would move north or south as required. However, most
>mammal specie do not do this. For good reason.
>
>Any mammal specie needing to adapt to a higher latitude will
>need a number of
>simultaneous genetic adaptations to meet the basic requirements
>of the latitude
>concerned.
>
>For example, a mammal specie moving from an equatorial climatic
>zone at sea level
>to a semi-equatorial climatic latitude, will need to adapt to at
>least four different
>climatic conditions. These comprise a reduction in average
>annual temperature,
>reduced humidity, seasonal changes and changes in day length. As
>a result, four
>simultanous genetic adaptations are required.
>
>However, there is an alternative route to a higher latitude
>which would involve fewer
>simultaneous adaptions. In this respect, the specie could adapt
>first to a higher
>altitude on the equator, and then adapt to a higher latitude. In
>such a case, a move
>from an equatorial latitude to a semi-equatorial altitude would
>only require two
>simultaneous adaptations. As the semi-equatorial altitude is
>still on the equator, the
>specie would only need to adapt to a reduction in annual average
>temperature and a
>reduced humidity level.
>
>When the specie had adapted to the semi-equatorial altitude, it
>could then adapt to
>the semi-equatorial latitudes. This would only require a further
>two simultaneous
>adaptations. Obviously, two simultaneous adaptations are far
>more likely than four
>simultanous adaptions. So the altitudinal-latitudinal adaptive
>route is the one taken
>by most mammal specie. Hominids would be no exception to the
>rule.
>
>It should be noted that Mount Kenya on the equator, has a full
>range of climatic
>zones ranging from equatorial at its base, to polar at its peak.
>
>When a specie has moved north or south to a higher latitude, it
>then spreads east
>and west throughout the global climatic zone. Only when the
>whole of the latitudinal
>habitats are completely populated will there be any need for a
>further
>altitudinal-latitudinal adaptation.
>
>During global cold periods the latitudinal climatic zones are
>moved towards the
>equator. The terrestrial specie tend to remain in their
>respective climatic zones, so
>they also move towards the equator. This creates a population
>squeeze in the
>equatorial regions - at all altitudes. As a result, it is during
>these global cold periods
>that the altitudinal - latitudinal adaptations on the equator
>tend to take place.
>
>So there is no altitudinal adaptive continuum. Specie will only
>adapt to a new
>equatorial altitude when they have to. As long as they can
>migrate north or south
>within the climatic zone, this will be the preferred line of
>adaptive migration. As the
>global cold periods come at infrequent intervals, the
>altitudinal adaptations are
>similarly infrequent.
>
>
>Fossil evidence implies that H. erectus adapted to the warm
>temperate altitudes and
>latitudes. The general consensus of paeleontological opinion
>seems to be that H.
>archaic was an adaptation to the cold temperate latitudes, while
>H. neanderthal was
>an adaptation to tundra latitudes.
>
>If this is correct, it would appear that the colonization of the
>tundra altitude and
>latitude was the last habitat adaptation. So the question arises
>as to the status of the subsequent hominid adaptations. In this
>context, it should be noted that an ecological niche is not
>solely a habitat. It is also a behaviour. For this reason, there
>can be many different ecological niches in the same habitat.
>
>By implication, it would appear that the H. sapiens adaptation
>was a behavioural
>adaptation rather than a habitat adaptation. If this was so,
>then H. neanderthal and H. sapiens would be complementary specie
>within the same habitat. This would be
>similar to the situation of the Gorilla and Bonobo, which are
>closely related specie
>inhabiting the same equatorial habitat. A further implication is
>that H.ss was also a
>behavioural adaptation, this time occupying a complementary
>niche in the cold
>temperate climatic zone. Here it would share its habitat with H.
>archaic.
>
>And so to the questions.
>
>1. Was H. archaic a cold temperate climatic adaptation?
>
>2. Was H. neanderthal a tundra climatic adaptation?
>
>3. Is there any evidence of seasonal migrations concerning
>either of the above
>specie?
>
>4. Was H. sapiens a behavioral adaptation to a tundra habitat?
>Is there any evidence
>that it was contemporary with H. neanderthal?
>
>5. Likewise, is there any evidence that H.ss was contemporary
>with H. archaic?
>
>6. In view of the evidence of habitat destruction by H.ss, could
>this behaviour have
>started at the inception of the specie?
>
>John.
>
>John Waters is the author of "Helpless as a Baby",
>a book concerned with general and human
>evolution. It may be accessed at URL
>http://www.dircon.co.uk/jdwaters/HAAB.htm
>
>jdwaters@dircon.co.uk
I see a difficulty in the theory.
I think there is a fifth climatic adaption, and very important indeed.
Moving north the uvb radiation
is much reduced, and the uvb radiation is essential
for the synthesis of vitamin D and the fixation
of calcium in the bones. So moving in latitude from the ecuator
the human skin need to become lighter to
improve the absortion of the uvb radiation.
But in altitude the effect is the contrary : uvb radiation
increases, so there is better for the human being to have a darker skin...
Anton Uriarte
Department of Geography, Prehistory and Arqueology
University of the Basque Country.
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