ANTHROPOLOGY: ON HUMANS AND RACE
ScienceWeek http://scienceweek.com
The following points are made by D.A. Hughes et al (Current
Biology 2004 14:R367):
1) Systematists have not defined a "type specimen" for humans, in
contrast to other species. Recent attempts to provide a
definition for our species, so-called "anatomically modern
humans", have suffered from the embarrassment that exceptions to
such definitions inevitably arise -- so are these exceptional
people then not "human"? Anyway, in comparison with our closest-
living relatives, chimpanzees, and in light of the fossil record,
the following trends have been discerned in the evolution of
modern humans: increase in brain size; decrease in skeletal
robusticity; decrease in size of dentition; a shift to bipedal
locomotion; a longer period of childhood growth and dependency;
increase in lifespan; and increase in reliance on culture and
technology.
2) The traditional classification of humans as Homo sapiens, with
our very own separate family (Hominidae) goes back to Carolus
Linnaeus (1707-1778). Recently, the controversial suggestion has
been made of lumping humans and chimpanzees together into at
least the same family, if not the same genus, based on the fact
that they are 98-99% identical at the nucleotide sequence level.
DNA sequence similarity is not the only basis for classification,
however: it has also been proposed that, in a classification
based on cognitive/mental abilities, humans would merit their own
separate kingdom, the Psychozoa (which does have a nice ring to
it).
3) As for sub-categories, or "races", of humans, in his Systema
Naturae of 1758 Linnaeus recognized four principal geographic
varieties or subspecies of humans: Americanus, Europaeus,
Asiaticus, and Afer (Africans). He defined two other categories:
Monstrosus, mostly hairy men with tails and other fanciful
creatures, but also including some existing groups such as
Patagonians; and Ferus, or "wild boys", thought to be raised by
animals, but actually retarded or mentally ill children that had
been abandoned by their parents. In his scheme of 1795, Johann
Blumenbach (1752-1840) added a fifth category, Malay, including
Polynesians, Melanesians and Australians.
4) Blumenbach is also responsible for using the term "Caucasian"
to refer in general to Europeans, which he chose on the basis of
physical appearance. He thought Europeans had the greatest
physical beauty of all humans -- not surprising, as he was of
course European himself -- and amongst Europeans he thought those
from around Mount Caucasus the most beautiful. Hence, he named
the "most beautiful race" of people after their supposedly most
beautiful variety -- a good reason to avoid using the term
"Caucasian" to refer to people of generic European origin
(another is to avoid confusion with the specific meaning of
"Caucasian", namely people from the Caucasus).
5) The extent to which racial classifications of humans reflect
any underlying biological reality is highly controversial;
proponents of racial classification schemes have been unable to
agree on the number of races (proposals range from 3 to more than
100), let alone how specific populations should be classified,
which would seem to greatly undermine the utility of any such
racial classification. Moreover, the apparent goal of
investigating human biological diversity is to ask how such
diversity is patterned and how it came to be the way that it is,
rather than how to classify populations into discrete "races".(1-
4)
References:
1. Nature Encyclopedia of the Human Genome. (2003). Cooper, D.
ed. (Nature Publishing Group),
2. Fowler, C.W. and Hobbs, L. (2003). Is humanity sustainable?.
Proc. R. Soc. Lond. B. Biol. Sci. 270, 2579-2583
3. Encyclopedia of Human Evolution and Prehistory. (1988).
Tattersall, I., Delson, E., and Van Couvering, J. eds. (Garland
Publishing)
4. World Health Organization Website http://www.who.int
Current Biology http://www.current-biology.com
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Related Material:
HUMAN EVOLUTION: A FUNCTIONAL HUMAN-APE GENETIC DIFFERENCE
The following points are made by Pete Currie (Nature 2004
428:373):
1) Ever since the famous occasion in the 19th century in which
Bishop Wilberforce ridiculed the possibility that man was
descended from apes, and the biologist T. H. Huxley (1825-1895)
bravely chose primate ancestry rather than ignorance, the debate
over our origins has claimed a special place in evolutionary
theory. With the acceptance by most of us that we are indeed a
product of natural selection, discussions surrounding the issue
have cooled somewhat. But exactly how natural selection acted to
produce the modern human form has remained hotly contested.
2) Stedman et al(1) describe what may be the first functional
genetic difference between humans and apes. Remarkably, the
timing of the appearance of this genetic alteration, or mutation,
roughly coincides with the appearance of "human-like"
characteristics in the hominid fossil record, and the authors
present convincing arguments as to how the mutation could have
been responsible for their acquisition.
3) The evolution of the genus Homo is associated with the
appearance of several defining features or traits, which set the
species within it apart from our more distant ancestors(2). Among
these morphological innovations is a reduced reliance on powerful
masticatory (jaw) muscles as a means of breaking down food. Large
jaw muscles are a feature of a number of genera of the family
Hominidae. These include living primates and extinct forerunners
of Homo, such as Paranthropus and Australopithecus, which are
believed to possess many features more allied to extant apes. By
contrast, a relatively slight masticatory apparatus is associated
with the fossil remains of species within Homo and modern humans,
and the advent of this morphological transition is closely
correlated with a dramatic increase in cranial capacity.
4) How exactly did this shift in cranial morphology come about?
By analyzing gene sequences in the human genome, Stedman et al(1)
have identified a new member of the class of genes that encode
myosin heavy chain (MYH) that may be associated with this change.
Myosin heavy chains are a critical protein component of the
sarcomeres, the "engine room" of skeletal muscle from which
contractile force is derived. There are numerous types of myosin
heavy chain specialized for the different muscle-contraction
rates specific for different muscles. The inactivation of
individual MYH genes, either in gene "knockout" mutant mice or in
human disease, often results in a dramatic reduction in the size
of the muscles in which they are active(3-5).
5) The particular gene in question, MYH16, is specifically
expressed in the jaw muscles of humans and monkeys. But,
surprisingly, a mutation in the human gene prevents the
accumulation of MYH16 protein. Stedman et al(1) found that, by
contrast, all non-human primates for which genome sequence could
be obtained have an intact copy of the gene, and have a high
level of MYH16 protein in their jaw muscles. An analysis of the
time at which the mutation arose during hominid evolution places
it at about 2.4 million years ago, the period just before the
evolution of the modern hominid cranial form. These findings
suggest a seductive hypothesis: that a decrease in jaw-muscle
size, produced by inactivation of MYH16, removed a barrier to the
remodeling of the hominid cranium which consequently allowed an
increase in the size of the brain.
References (abridged):
1. Stedman, H. H. et al. Nature 428, 415-418 (2004)
2. Wood, B. Nature 355, 783-790 (1992)
3. Acakpo-Satchivi, L. et al. J. Cell Biol. 139, 1219-1229 (1997)
4. Allen, D. L., Harrison, B. C., Sartorius, C., Byrnes, W. C. &
Leinwand, L. A. Am. J. Physiol. Cell Physiol. 280, C637-C645
(2001)
5. Martinsson, T. et al. Proc. Natl Acad. Sci. USA 97, 14614-
14619 (2000)
Nature http://www.nature.com/nature
--------------------------------
Related Material:
ON HUMAN EVOLUTION
The following points are made by Ian Tattersall (Scientific
American 2001 December):
1) When we contemplate the extraordinary abilities and
accomplishments of Homo sapiens, it is certainly hard to avoid a
first impression that there must somehow have been an element of
inevitability in the process by which we came to be what we are.
The product, it's easy to conclude, is so magnificent that it
/must/ stand as the ultimate expression of a lengthy and gradual
process of amelioration and enhancement. How could we have got
this way by accident? If we arrived at our exalted state through
evolution, then evolution must have worked long and hard at
burnishing and improving the breed, must it not?
2) Yet that seems not to be how evolution works; for natural
selection is not -- it cannot be -- in itself a creative process.
Natural selection can only work to promote or eliminate novelties
that are presented to it by the random genetic changes
(influenced, of course, by what was there before) that lie behind
all biological innovations. Evolution is best described as
opportunistic, simply exploiting or rejecting possibilities as
and when they arise, and in turn, the same possibility may be
favorable or unfavorable, depending on environmental
circumstances (in the broadest definition) at any given moment.
There is nothing inherently directional or inevitable about this
process, which can smartly reverse itself any time the fickle
environment changes.
Scientific American http://www.sciam.com
ScienceWeek http://scienceweek.com
--
Best,
Frederick Martin McNeill
Poway, California, United States of America
mmcneill@fuzzysys.com
http://www.fuzzysys.com
http://members.cox.net/fmmcneill/
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Phrase of the week :
There are living systems; there is no "living matter".
-- Jacques Lucien Monod (1910-1976)
:-))))Snort!)
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