tists; in other words, from a perspective ‘within the subculture’. This is
evident if we compare Poulton’s
New Scientist
article with opening para-
graphs of the professional text on which it is based, (‘Mitochondrial DNA
and Human Evolution’, by Rebecca L. Cann, Mark Stoneking and Allan C.
Wilson, in
Nature,
Vol. 325: 1 January 1987):
Molecular biology is now a major source of quantitative and objective
information about the evolutionary history of the human species. It has
provided new insights into our genetic divergence from apes,1–8 and
into the way in which humans are related to one another genetically.9–
14 Our picture of genetic evolution within the human species is
clouded, however, because it is based mainly on comparisons of genes
in the nucleus. Mutations accumulate slowly in nuclear genes. In
addition, nuclear genes are inherited from both parents and mix in
every generation. This mixing obscures the history of individuals and
allows recombinations to occur. Recombination makes it hard to trace
the history of particular segments of DNA unless tightly linked sites
within them are considered.
Our world-wide survey of mitochondrial DNA (mtDNA) adds to
our knowledge of the history of the human gene pool in three ways.
First, mtDNA gives a magnified view of the diversity present in the
human gene pool, because mutations accumulate in this DNA several
times faster than in the nucleus.15 Second, because mtDNA is
inherited maternally and does not recombine,16 it is a tool for relating
individuals to one another. Third, there are about 10 16 mtDNA
molecules within a typical human and they are usually identical to
one another.17–19 Typical mammalian females consequently behave
as haploids, owing to a bottleneck in the genetically effective size of
the population of mtDNA molecules within each oocyte.20 This
maternal and haploid inheritance means that mtDNA is more
sensitive than nuclear DNA to severe reductions in the number of
individuals in a population of organisms.15 A pair of breeding indi-
viduals can transmit only one type of mtDNA but carry four haploid
sets of nuclear genes, all of which are transmissible to offspring. The
fast evolution and peculiar mode of inheritance of mtDNA provide
new perspectives on how, where and when the human gene pool
arose and grew.
This research article introduction follows the now-familiar generic moves
identified by Swales (1981, 1990): in brief, the centrality of the topic is iden-
tified, past research is summarised (the sources are referenced via
endnotes, indicated by the superscript numbers), a gap in the research is
indicated, and the findings of the research previewed. This kind of analysis
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the journal
Nature
, written by James Watson and Francis Crick (reprinted in
Bazerman, 1988: 49–50), proposing a double helix structure for DNA,
confirms this. The article ‘suggests’ a structure for DNA and in the short
letter the tentative vocabulary of perception and belief – ‘appears’, ‘in our
opinion’, ‘we believe’ – figure largely. Generous credit is given to fellow
researchers in different institutions, many who have ‘kindly’ given access
to unpublished research; and the main claim to knowledge – that the
proposed structure of DNA solves the problem of how genetic material is
reproduced – is couched in the modest phrase ‘it has not escaped our
notice’. It is a triumphalist modesty, given that the article reports one of the
major scientific discoveries of all time, but modesty it is: the rhetorical con-
ventions of professional science demand that face-threatening claims are
avoided, and that due deference is paid to the scientific community as a
whole (cf. Myers, 1989, 1990). The community itself is represented as an
altruistic, sharing group of rational colleagues. This is not necessarily the
view presented in other genres that represent scientific activity.
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