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No. 215 "Vital Articles on Science/Creation" May 1991
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PATTERNS OF SPECIATION
by Kenneth B. Cumming, Ph.D.*
Copyright (c) 1991 by I.C.R.
All Rights Reserved
* Dr. Cumming is Professor of Biology and Dean of the Institute for
Creation Research Graduate School.
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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.
Endler[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.
Essentialism
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
saltational origins of new essences."
Overview
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
lest, 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 reproducive 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 macro-evolution, without knowing very
well how either takes place, or the causative relation between the two.
Modes of Speciation
Mayr[11] lists twelve potential modes of speciation, not all of which
ave been observed (reworded below by author).
Potential Modes of Speciation
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
hem 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
ource of evolutionary change; and population events, like evolution as
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.'"
Summary
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 still 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."
-- References --
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.
________________________________________________________________________
This "Impact" was converted to ASCII, for BBS use,
from the original formatted desktop article.
Comments regarding typographical errors
in the above material are appreciated.
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