Review of Species Problem
Previously, 1
a sample of definitions for the term "species" was given.
Presuppositions for each definition seem to be important in establishing
the validity, or at least usefulness, of any particular definition.
Endear 2 concludes: "It
is clear that species concepts vary radically depending on their
purpose, be it theoretical or operational, taxonomic or evolutionary,
contemporaneous or clade, reproductive or cohesive. It is unproductive,
and often positively misleading, to apply one species concept
to all species, or to answer all questions."
Notice that the definitions of species as used above
hinge on their explanatory power for evolutionary phenomena. If
speciation were real, but subject to finite limits of variation,
then microevolution very well might be confirmed without the collateral
concept of macroevolution being established at all. A creationist
view allows for some speciation because of the wide range of definitions,
but does not support higher taxonation.
A variety of terms have been used in the past to
describe species for the limited view of variation: immutable,
3 constancy, 4
essences, 5 fixity, 6
types, 7 and kinds. 8
The underlying idea is that organisms are grouped by limited expressions,
such that gaps exist between fundamental groups. Today's young
earth creationist is not a strict essentialist, in that variation
is expected and thoroughly acknowledged. On the other hand, gaps
between groups are said to be common, and seldom, if ever, bridged.
Mayr 9 reviews the contrast
of thoughts: "Essentialism with its emphasis on discontinuity,
constancy, and typical values ("typology"), dominated
the thinking of the western world to a degree that is still not
yet fully appreciated by the historians of ideas. Darwin, one
of the first thinkers to reject essentialism (at least in part),
was not at all understood by the contemporary philosophers (all
of whom were essentialists), and his concept of evolution through
natural selection was therefore found unacceptable. Genuine change,
according to essentialism, is possible only through the saltation
of new essences."
Speciation, like its parent concept, evolution,
is said to be a fact, even though few beginning-to-end examples
can be given for it. Bush 10
states: "Furthermore, speciation is usually a rare event,
seldom, if ever, observed from start to finish. Our current concepts
of speciation are therefore primarily based on post hoc reconstructions
of past events, or derived from theoretical population genetic
models usually based on classical Mendelian genetics, with all
the inherent weaknesses and speculative nature of these approaches.
The post hoc approach is, at best, subjective, and it is
thus not surprising that recent advances in molecular biology
call into question certain widely held conclusions of the naturalists
and population geneticists (Crick, 1979)."
This is not to deny that speciation occurs. Much
evidence implies that isolating processes are establishing
unique populations all the time. Indeed, in the case of ploidy,
a new isolated species (depending on the definitions) can occur
in one generation. However, if speciation (primarily reproductive
isolation) is the process of microevolution, and, in turn macroevolution,
as some proponents hold, then we are once again in the precarious
position of declaring that the fact of speciation leads directly
to the fact of macroevolution, without knowing very well how either
takes place, or the causative relation between the two.
Mayr 11 lists
twelve potential modes of speciation, not all of which have been
observed (reworded below by author).
Transformation of single species
1. Single species transformation by mutations, etc.
2. Single species transformation by genetic input from a second
species
3. Fusion of two species by hybridization into a single species
Multiplication of species by unique events
1. Asexual species mutating into a new species
2. Macrogenesis or hopeful-monster production
3. Chromosomal aberrations leading to new species
4. Chromosomal set multiplication within a species
5. Chromosomal set combining between species
Multiplication of species by population events
1. New species formed within single populations
- sympatry
2. New species formed at hybrid zones - semigeographic
3. New species formed by geographically isolated populations
4. New species formed by extinction within the range of the species.
The first three modes only involve the change of
starting species totally into following species without branching.
The next five modes involve speciation events that are peculiar
in mechanics. The last four modes involve populations which are
said to give rise gradually to more than one new species through
branching. Mayr gives no detailed examples of each of these modes
at this citation, but does offer some general conclusions: First,
speciation has come to mean principally the multiplication of
species; therefore, phyletic speciation (single species transformation)
is not of particular interest to evolutionists. Fusion of species
is a retrograde process for evolution, and simply may be the breeding
of subspecies that were incompletely identified.
Asexual species formation is complicated by the
very definition of species, which is assigned, most generally,
to reproductively isolated populations. Since vegetative processes
are involved, every individual is reproductively isolated from
all others at the outset. Commonly, such organisms are said to
belong to a collective species.
Macrogenesis is not known from real data, but is
rather an hypothetical construct. Many monsters have been born,
but none are known to have given rise to new species lines.
Chromosomal alterations, either in structure or
number, are common. Indeed, the only direct evidence for speciation
is found in the formation of polyploid organisms. Multiple sets
of chromosomes make them unable to cross with the parent species;
hence they become new species, even though they might look and
behave very much like the parental lines.
Most speciation is said to be associated with gradual
population changes under the influence of geographical differences.
The mechanisms for such speciation is hotly disputed, even though
the population data seem to indicate definite levels of divergence
or subspecies formation. Mayr concludes, on page 513: "The
widespread occurrence of geographic speciation is no longer seriously
questioned by anyone."
Once again, we come to a dissettling conclusion
regarding the process of speciation. Transformation within single
species is not of highest importance to evolution; unique speciation
events are not a major source of evolutionary change; and population
events, like evolution as a whole, are said to be difficult to
observe. Hard evidence (start to finish) for speciation as a major
process in evolution is obviously lacking.
Mayr, on page 48 comments: "Speciation is a
slow historical process and, except in the case of polyploidy,
it can never be observed directly by an individual observer. .
. . The method [of construction] most suitable for our purpose
consists in the reconstruction of an essentially continuous series
by arranging fixed stages in the correct chronological sequence.
. . . Stating our aim more specifically, it should be possible,
speciation being a slow process, to find natural populations in
all stages of 'becoming species.'"
The wide variety of definitions for the term species
today permits one to conclude that some new species are being
formed from old species. Thus, speciation supporting microevolution
(horizontal change), is an acknowledged phenomenon. However,
the critical category of speciation that would establish macroevolution
(vertical change) is said to be difficult to document as a totally
observed event. Although much literature has been written to illustrate
the concept, most of it is inferential. Even in these writings,
a credible extrapolation of these transformations to establish
higher taxonation above the species level is very suspect.
Today's creationist interpretation of speciation
would be given in an essentialist perspective claiming that even
though the ancient "fixity of species" dogma is disproved
by speciation events, there are also practical limits to so-called
"phyletic" change. These limits are seen in the historic
and current documentation of discontinuities between types. This
subject will be the theme of an upcoming article on "specialization."
[1] K. B. Cumming, "On
the Changing Definition of the Term 'Species,'" Acts
& Facts "Impact" No. 211 (1991); pp. i-iv.
[2] J. A. Endler, "Conceptual and
Other Problems in Speciation," in D. Otle and J. A. Endler,
Speciation and Its Consequences, (Sunderland, Massachusetts,
Sinauer, 1989), pp. 625-648.
[3] D. Kohn, "Theories to Work
By: Rejected Theories, Reproduction, and Darwin's Path to Natural
Selection" in W. Coleman and C. Limoges, Studies in
History of Biology (Baltimore, Maryland, The Johns Hopkins
University Press, 1980), p. 69.
[4] J. Phillips, Life on the Earth
(New York, Arno Press, 1980), pp. 191, 194 [Originally prepared
in 1860].
[5] E. Mayr, "The Nature of the
Darwinian Revolution," Science, 166 (1972): pp.
981-989.
[6] M. Denton, Evolution: A Theory
in Crisis (London, England, Burnett Books, 1985), pp. 17-367
[particularly p. 19].
[7] C. Lyell, Principles of Geology
(New York, D. Appleton and Co., 1853 Ninth Ed.), pp. 578-590
[particularly p. 579].
[8] H. Morris, Ed., Scientific Creationism
(El Cajon, California, Master Books, 1984, Eleventh Ed.),
pp. 51-54.
[9] E. Mayr, The Growth of Biological
Thought (Cambridge, Massachusetts, The Belknap Press, 1982),
p. 38.
[10] G. Bush, "What Do We Really
Know About Speciation?" in R. Milkman, Perspectives
on Evolution (Sunderland, Massachusetts, Sinauer, 1989),
pp. 119-128 [particularly pp. 119, 120].
[11] E. Mayr, Animal Species and
Evolution (Cambridge, Massachusetts, The Belknap Press,
1979), pp. 428, 488, 513.* Dr. Cumming is Professor of Biology
and Dean of the Institute for Creation Research Graduate School.
