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About the Book
Table of Contents
Part I
Part II
Part III
Part IV
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Part IV: The Fitness of Living
Things: Dauermodifications
Chapter 3
Evidence for Dauermodifications Below
Man
THERE IS A built-in stability accompanied by a responsiveness
to environmental pressures in all living things � plants,
animals, and man. This built-in stability guarantees order and
therefore a measure of predictability which provides man with
the means of controlling the development of things to his own
advantage. Responsiveness, on the other hand, fits all these
creations of God to their physical world and to one another,
to produce a grand harmony. The former is maintained through
nuclear inheritance; the latter is achieved through cytoplasmic
inheritance.
It has always been
obvious enough, really. Naturalists of an older generation with
Christian leanings saw in the fitness of things evidence of God's
directive providence at work. Evolutionists later came to attribute
this fitness entirely to the operation of chance, rejecting the
idea of direct intervention of the Creator. Today it seems that
we may once again be in a position, on the basis of hard evidence,
to recognize a mechanism by which both stability and adjustment
are combined to allow a measure of freedom of variation in form
and function without inviting a total breakdown of order.
The ability of
plants to acquire a new character which enhances fitness, and
to pass it on to succeeding generations as long as the environment
favours it, has been recognized for many years. It was the transient
character of this kind of inheritability that defied explanation
in conventional Mendelian terms. Yet it is this transient character
which seems so necessary to ensure fitness when environmental
conditions change. The environment is changed, not merely when
a shift in temperature or humidity occurs, but also when a species
is forced to migrate into a new habitat due to the pressure of
numbers or other competing forms of life. In
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either case, from the
point of view of a particular species, the environment has changed
and it is essential that the species adjust or become less fit
to survive.
Julian Huxley many
years ago remarked upon the fact that plants are able to make
this kind of adjustment when they are transplanted. He noted
that dandelions whose natural habitat was lowland country changed
their size, form, and proportions surprisingly quickly when transplanted
to a higher altitude. (20) But the adjustment was transitory, for if these
modified plants were then returned to their former habitat, they
quite quickly recovered their previous size and form. This phenomenon
is common enough in nature. Since the nuclear genes remain constant,
the change in either direction has to be attributed to some factor
in the cytoplasm.
The change in such
a case is rapid but not always immediate, and the reversion to
type follows the same course. Such a circumstance can only be
accounted for on the basis of some kind of inheritableness, since
it is progressive and carried over cumulatively. Had mutations
of nuclear genes been involved, the effect would be instantaneous
rather than occupying several generations. Slow adjustment, even
if it occupies only two or three generations, clearly indicates
a carry-over effect which demands explanation in terms of some
inheritable influence. These dandelion observations ought to
have suggested non-nuclear inheritance, but the climate of opinion
did not allow such a suggestion � or if it was made, it did
not gain a serious hearing.
Now, for many years
there has tended to be far greater popular interest in animals
than in plants, because the theory of evolution has occupied
such a large place in our thinking and comparatively few people
connect the theory with plant life. The renewed possibility of
the inheritance of acquired characters in animals has begun to
excite more interest in recent times, because it could provide
an alternative to natural selection as the modus operandi
of progressive change. An increasing number of authorities
are having second thoughts about the adequacy of the concept
of natural selection today, and cytoplasmic inheritance would
seem to provide a new and exciting alternative.
It often happens
that when an idea which has hitherto been repudiated begins to
receive more favorable attention, a whole wealth of new evidence
in its favour is suddenly discovered. It is certain that a number
of authorities whose standing in the scientific community is
unchallengeable have for some time been questioning the validity
of natural selection as an explanation of the fitness of things.
Lucien Cuenot in France,
20. HuxIey, Sir Julian, ref.6, pp.36-37.
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Wood Jones and Sir Alister
Hardy in England, W. R. Thompson in Canada, and many others have
openly challenged it. (21)
The factors which
cause modification tending to greater fitness are observed in
animal species at every level of complexity. The pressures which
operate to spark these adjustments are of at least three kinds:
climatic (which would include environmental temperature, humidity,
altitude, wind, etc.); biotic (other living things which exert
selective pressures due to predation, crowding, altered breeding
habits, etc.); and edaphic (the nature of the rocks and the soil
insofar as they influence the types of food available, their
varying nutritional character, and the kind of water).
Sir Cyril Hinshelwood
has shown that even such lowly forms as bacteria respond to such
pressures. (22) Various
kinds of bacteria will "learn" to cope with a new food
or poison and will transmit their acquired biochemical wisdom
more or less durably (according to the number of cell generations
for which the treatment has been applied) to their descendants.
We are only too well aware of the fact that various insecticides
applied to plants � and antibiotics applied to ourselves
� tend to lose their potency if they are used in one form
for too long a period. The organisms under attack develop an
immunity (or fitness, from their point of view) without becoming
specifically different at a species level. Only by modifying
the treatment every so often can they be held in check by reason
of the constant upsetting of the mechanism of adjustment whereby
they are able to develop immunity. This is clearly a case of
dauermodification.
But it is not merely
in these lower forms of life that we observe this phenomenon.
We have a number of instances of species of frogs or salamanders
which have gradually spread along either side of some natural
barrier such as a mountain or a lake and diverged sufficiently
as they spread that, when they were again brought into contact
at the far end of the barrier, they show themselves to be no
longer a naturally interbreeding community. (23) The two populations that demonstrably began as one
are now isolates and
21. See Lucien Cuenot, L'evolution biologique:
les faits, les uncertitude. Masson, Paris, 1951; F. Wood
Jones, Trends of Life, Arnold, London, 1953; Sir Alister
Hardy, The Living Stream, Collins, London, 1965; W. R.
Thompson, introduction to Centennial edition of Darwin's Origin
of Species, Dent, New York, 1959.
22. Sir Cycil Hinshelwood: quoted by Donald Michie, "The
Third Stage in Genetics" in A Century of Darwin,
ed. S. A. Barnett, Heineman, London, 1958, p. 65.
23. Frogo: Maynard Smith, The Theory of Evolution, Penguin,
Harmondsworth, England, 1958, p. 189; and salamanders, Edward
Dodoun, A Textbook of Evolution, Saunders, Philadelphia,
1952, pp. 318,321.
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continue to be so even
though sharing a single habitat again. This separateness may
stem from several causes, depending upon the particular route
taken by the migrating sub-populations. A different food supply
along the way may induce different tastes that become inherited
and persist. This in turn may cause a divergence in body
odour (24) or size
or coloration or mating calls or other changes (25) which are preserved by the two divergent lines even
after they come together again in a single habitat. The new tastes
may in no way affect the fitness of the individual, and there
will therefore be no immediate pressure tending to its reversion.
It is clear that
such divergent subspecies are still genetically a single species,
for it can be shown in many cases that they will interbreed in
the laboratory. (26) Yet,
for what might be called psychological reasons, (27) they no longer do so in
nature. It seems likely that in some instances the single habitat
shared by both subspecies will tend to draw them together again;
but this does not necessarily happen, since their divergent forms
may both be very well-suited to their survival so that there
is no pressure driving them toward convergence again. The persistence
of the divergent forms under these circumstances is clearly an
example of dauermodification. T. M. Sonneborn notes that: (28)
Differing conditions for mating
reactivity (temperature, light), once they arise, constitute
such effective barriers to interbreeding that different varieties
(of protozoa) can and do intimately coexist in the same body
of water without losing their integrity. Even when the mating
type specificities are only slightly different and interbreeding
is possible, the varieties are found to coexist in the same body
of water in nature. From these observations, it would seem that
even relatively slight changes in mating type specificity could
lead to isolation of a new variety.
- The opposite
of a divergence is convergence. In this case, two distinct species
which cannot be shown to have a common ancestry may increasingly
become alike in form and function as a result of sharing similar
needs under similar environmental conditions. Some of the evidence
of this well-established phenomenon is
-
- 24. Dodson, Edward, ref. 23, p. 321.
- 25. Moore, John A., "An Embryologist's
View of the Species Concept" in The Species Problem,
edited by Ernst Mayr, A.A.A.S., Washington, D.C., 1957, p.329.
- 26. Dodson, Edward, ref.23, p.318.
- 27. See New Scientist, 26 February,
1976, p.439 under the heading "Green Toads Sing their Way
through Evolution." The frequency and pitch of the toad's
mating call is modified by the range of temperature within which
the young are matured, and only toads with the appropriate calls
any longer attract one another. The community is therefore broken
up somewhat by the effects of different temperatures on the young.
- 28. Sonneborn, T. M., "Breeding Systems,
Reproductive Methods, and Species Problem in Protozoa" in
The Species Problem, edited by Ernst Mayr, A.A.A.S., Washington,
D.C., 1957, p.233.
pg.4
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examined in a previous volume in this
series. (29) Such
a mechanism must also involve the principle of dauermodification;
otherwise each generation would have to start from scratch and
the offspring would be born without the advantages accruing from
their parents' experience. The gains would not be cumulative.
But we know that such gains are cumulative, because the neonate
is usually found to bear in miniature most of the structures
which the adult has acquired to its own advantage. For example,
a number of animals which live in and out of water display an
alignment of nostrils, ears, and eyes that permits them to submerge
themselves almost entirely below the water while yet being able
to breathe and see and hear what goes on around them. The hippopotamus
and the crocodile are among such animals, and their young
are similarly equipped.
F. Wood Jones wrote
eloquently about many of these examples of fitness of animals
for the kind of lives they live. But unfortunately he attributed
it to what can best be described as a kind of mystical goal-seeking
drive in all living things directed toward satisfying needs begotten
by the circumstances of ecological demands. He commented: (30)
Exactly how these could be explained
on the supposition that structural alterations are due solely
to random genetic variations acted on by "natural selection"
determining the "survival of the fittest" in a "struggle
for existence" is a thing which seems very difficult to
conceive.
It is a principle
broadly applied in the history of the development of scientific
ideas that a useful theory is not overthrown by the mere citation
of contrary evidence, but only by the presentation of a better
theory. Natural selection, rightly or wrongly, is a concept which
has much to commend it. It appeals to our sense of the obvious,
and in terms of human experience the history of man seems to
bear it out. Moreover, it can be made rational justification
for the powerful among men to exhibit freely some of the worst
aspects of human nature.
But it is not at
all certain that animal nature and human nature are the same.
What is appropriate in nature may not at all be appropriate in
human society, so that neither the reasonableness nor the unreasonableness
of the concept of natural selection in human terms has any real
bearing on whether it is an appropriate concept to apply in nature.
Man is a fallen creature, and his present behaviour makes him
unnatural by almost every
29. 0n this, see "Convergence and the Origin of
Man," Part III
in Evolution or Creation?, vol.4 in The Doorway Papers Series.
30. Jones, F. Wood, ref. 21, p. 84.
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standard of judgment.
We do not find the struggle to survive in nature taking the same
form as it does in human society. There is no certainty that
nature is ruthless in the sense that human society constantly
tends
to be.
The fitness of
things in nature is everywhere apparent. The un-fitness of man
is also everywhere apparent.
One would suppose that if man is really part and parcel of the
web of nature, he will become increasingly fit by the same kind
of dauermodifications. There is some evidence that such modifications
do indeed improve man's fitness, but there is the disruptive
factor of man's fallen nature constantly placing his survival
in jeopardy.
As we shall see
in the next chapter, man shares in the web of life to the extent
that dauermodifications at least contribute this much to his
well-being, namely, that he is better able to obey the command
to fill the earth and subdue it. It is dauermodifications that
have enabled him successfully to become truly ubiquitous. He
can thrive in any climate. It is a remarkable fact that wherever
dauermodifications can be demonstrated in man, they seem to serve
this purpose above all � which may be one more evidence of
benevolent design.
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Copyright © 1988 Evelyn White. All rights
reserved
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