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Part IV: The Fitness of Living
How Is Fitness Acquired?
THOSE WHO live nearest to nature never cease to wonder
at the fitness of living things. Until man intrudes, nature
seems replete with evidences of wise design. Every creature is
equipped with all the structures, all the skills, and all the
instincts necessary for its own continuance as part of the web
of life. Man alone appears to be an alien and a disturber.
The concept of
nature as "red in tooth and claw," which Tennyson introduced
in his poem In Memoriam some ten years before Darwin published
his Origin of Species, is increasingly being viewed today
as a travesty of the natural order. Probably the only reason
it has survived so long is that those who contributed most to
reinforce it by their writings, including Darwin himself, derived
too much of their knowledge of animal behaviour by observing
them in captivity. In the wild there is inevitably some shedding
of blood, but we now know that cruelty per se is almost
entirely absent. Death is avoided by all living things, and they
do not seem to live in fear of death, except where man
are extraordinarily sensitively fitted for the kind of lives
they live. To the Christian this is evidence of wise design,
but to the unbeliever it seems to demand some other explanation.
In many cases where the element of fitness is truly extraordinary,
it becomes extremely difficult to see how it could come about
purely by chance.
One of the earlier
students of nature who sought to account for this fitness without
any direct appeal to supernatural intervention was Jean Baptiste
Lamarck (1744 - 1829). In his Philosophie zoologique, published
in 1809, he reasoned that any animal could adjust itself structurally
to improve its fit with the environment and
pass on the advantageous adjustment
to its descendants. By a process akin to compound interest, each
generation improved upon
the fitness of the previous one and thus all living creatures
constantly enhanced their chances of survival ‹ not by a
process of elimination of the unfit, but by improving their own
fitness. This natural ability was resident within the constitution
of all living things. It was not a conscious goal-seeking which
might be confused with some form of teleology, but simply part
of the stuff of living. The important thing was that every gain
was inherited. "Lamarckianism" came to be defined simply
as "the inheritance of acquired characteristics," and
the acquired characteristics were modifications of structure
resulting to the benefit of the organism from the direct influence
of the environment.
In Darwin's time,
Lamarckianism was very widely accepted by those who by disposition
sought an explanation of fitness without appeal to supernatural
agency. Curiously, Darwin did not himself feel happy about it.
He sought for and found what he considered a better explanation
in the multiple concepts of Natural Selection, the Struggle to
Survive, and the Survival of the Fittest. In Darwin's view, Lamarckianism
was unrealistic, mystical, and not adequately borne out by the
facts. He saw the elimination of the unfit as a much more likely
and verifiable principle of improvement of a species. He did
not reject the inheritance of acquired characteristics, but he
questioned whether characteristics were ever acquired by the
mechanism Lamarck envisioned.
In the course of
time, however, Darwin himself gradually shifted his position
in this respect, and it is interesting to observe the change
in his thinking as reflected in his own written observations.
In 1861 he wrote: (1)
My greatest trouble is not being
able to weigh the direct effects of the long continued action
of changed conditions of life without any selection, against
the action of selection on mere accidental (so to speak) variability.
I oscillate much on this head, but generally return to my belief
that the direct action of the conditions of life has not been
great. At least this direct action can have played an extremely
small part in producing all the numberless and beautiful adaptations
in every living creature.
But one year later, on 24 November 1862, Darwin
wrote to Sir Joseph D. Hooker: (2)
I hardly know why I am
a little sorry, but my present work is leading me to believe
rather more in the direct action of physical conditions. I presume
I regret it because it lessens the glory of Natural Selection
and is so confoundedly doubtful.
- 1. Charles Darwin: Life and Letters, edited
by Francis Darwin, Murray, London, 1888, vol. II, p.369, in a
letter to T. Davidson dated 30 April.
- 2. Ibid., p.390.
reflected upon the matter and became convinced enough that ten
years later, when he published the sixth edition of his Origin
of Species he observed: (3)
Species have been modified .
. . chiefly through natural selection of numerous, successive,
slight, favourable variations, aided in an important manner by
the inherited effects of use and disuse of parts; and in an unimportant
manner . . . by the direct action of external conditions. . .
. It appears that I underrated the frequency of these latter
forms of variation as leading to permanent modificaions of structure
independently of natural selection.
In the first
edition of his Origin of Species (1859, chap.6, p.256),
Darwin had said that natural selection is "in some cases"
aided by the use and disuse of parts and "slightly affected"
by the direct influence of the environment. In the sixth edition
(1872, p.167) the words "in some cases" had become
"in many cases," and "slightly affected"
had become simply "affected." Four years later, in
1876, Darwin wrote in a letter to Moritz Wagner: (4)
In my opinion the greatest error
which I have committed has been not allowing sufficient weight
to the direct action of the environment, i.e., food, climate,
etc., independently of natural selection. . . . When I
wrote the Origin and for some years afterwards I could
find little good evidence of the direct action of the environment;
now there is a large body of evidence.
1877, in a letter to Melchior Neumayer dated 9 March, he wrote
concerning an example of direct influence of the environment
reported by his correspondent. "It is by far the best case which I have
ever met with showing the direct influence of life on the organism."
common-sense logic and the evidence he accumulated in support
of natural selection were persuasive enough that they prepared
the way for the final overthrow of Lamarckianism ‹ an overthrow
completed by the experiments of Auguste Weismann (1843-1914).
It had long been
recognized that modification of a parent body by artificial means
had no effect upon the offspring. Circumcision, for example,
had been practiced for thousands of years without leading to
a race of congenitally circumcised male children. The operation
still had to be performed in every generation. Still
3. Darwin, Charles, The Origin of Species
by means of Natural Selection, Murray, London, 6th edition,
1872, chap.15, p.42l.
4. Charles Darwin: Life and Letters, edited by Francis
Darwin, Murray, London, 1888, vol. III, p.159.
5. Ibid., vol. II, p.232.
there was a possibility
that the modification was not effectively passed on because only
the father of the next generation was involved, and not
the mother. If some comparable gross modification of the mother
had been repeated over the same period of time, the results might
have been different. However, it had been customary in China
for many centuries to bind the feet of female infants in the
upper classes of society. Small feet were considered beautiful.
Yet here again there was no evidence that the modification was
becoming inheritable. Clearly, modifying the male or the
female in such ways, even after centuries of repetition, did
not affect the germinal stream in any way, since no influence
upon subsequent generations had ever been observed.
In an attempt to
determine whether inheritance of such modifications or acquired
characters would occur if both sexes were modified in
the same way, Weismann cut off the tails of experimental mice
of both sexes, male and female, for many generations: he still
found that such a modification did not become inheritable. Thus
Julian Huxley remarked upon the apparent immunity of living organisms
against all experimental attempts to modify their characteristic
form in a way that would be self-perpetuating, underscoring the
fact that there seems to be no direct effect of the environment
upon the germ plasm. In 1938 Huxley observed, (6)
Can the hereditary constituents
be permanently changed by environment? It is clear that theoretically
it should be possible to induce such changes. The hereditary
constitution is seen to be something material which only our
lack of knowledge prevents us from defining chemically; and as
such it must be possible for us to alter it. The remarkable fact,
however, is its stubbornness in resistance in alteration.
Sixty-nine generations of flies
bred in the dark ‹a nd yet no alteration in their eyes or
their instincts with regard to light. Ninety generations in an
attempt to cause their resistance to heat by acclimatization
and selection ‹ without result. . . .
In spite of all the work that has been
done, we have only established that to a great many apparent
outward influences the germ plasm is quite unresponsive.
this was written four decades ago, but subsequent research has
only reinforced the conclusion. Insofar as the germ plasm and
nuclear genes are concerned, the results are still negative.
No experimental modification of the body cells seems capable
of bringing about inheritable changes in the nuclear genes of
the organism. As some wag is reported to have said when referring
to the negative results of Weismann's
- 6. Huxley, Sir Julian, "Inheritance
of Acquired Characteristics" in Essays in Popular Science,
Penguin, Harmondsworth, England. 1938, pp.36-37.
experiments, and with
apologies to Shakespeare's Hamlet: "There is a divinity
that shapes our ends, rough-hew them how we will."
Now it is possible
by deliberately damaging the nuclear genes to bring about
inheritable modifications. But this kind of interruption of the
normal development of an organism must be a comparatively rare
event in nature, (7) and when it does
occur it is even less likely that the effect will be beneficial.
Indeed, there are many geneticists who believe that all gene
mutations which result from this kind of interference with the
normal development of the organism are harmful. Individuals carrying
such harmful genes would tend to be eliminated in the natural
course of events, simply because they are less fit.
The amazing fitness
of organisms within their own particular habitat demands an explanation.
And the explanation must also account for the fact that living
things seem to have a large capacity for adjustment to environmental
pressures and seem to be able to pass on the benefit of these
adjustments by inheritance to succeeding generations. Since experimentally
it has not seemed possible to mimic nature in this respect by
effecting changes on nuclear genes we must suppose either that
there is some built-in mechanism of adjustment that is inheritable
by some other means than nuclear genes, or that God has been
at work creatively making these adjustments throughout the past.
Certainly the fitness
of things is everywhere manifest in nature and all the more manifest
as the circumstances are more carefully examined. Since the environment
tends to be in a state of flux, fitness must involve a similar
flexibility. The ideal mechanism would be one which can capture
and hold any successful adjustment made in one generation so
that the next generation can build upon it. Wood Jones was one
of those who argued strongly for this view, but despite his eloquence,
current orthodoxy ‹ having rejected Lamarck ‹ did not
allow him a hearing: he was arguing in favour of some form of
inheritance of acquired characters. (8) He was arguing, in fact, in favour of the view that
environmental pressures did have a direct effect on the
development of living forms over successive generations and not
merely an indirect effect through a process of natural selection
by elimination of the less fit.
7. The very persistence of many forms over
supposedly millions of years without significant change is evidence
of this. The stability of many organisms over enormous periods
of time is astonishing.
8. Jones, F. Wood, Trends of Life, Arnold, London, 1953,
especially chap.12, p.128, "The Inheritance of Adaptations."
negative evidence against the inheritance of acquired characters
under experimental conditions in the laboratory is not always
borne out by what goes on in nature. The contradiction may have
been unresolved in the past, because current theory has demanded
that nuclear genes provide the only pathway for inheritable
factors and these genes are remarkably immune to the direct influence
of environmental pressures, except those which are essentially
But in the past
few years a renewed interest in the possibility of another pathway
whereby the environment might have a direct influence upon an
organism responding in an inheritable way has led to the conclusion
that there are probably carriers of inheritable material in the
cytoplasm of the cell and not merely in the nucleus. These
carriers, which have been termed Plasmagenes, are responsive
to the direct action of the environment. This responsiveness
appears to be somewhat delayed, so that the environmental pressure
must be held constant over several generations to influence the
plasmagenes. That the response of these extra-nuclear genes can
be inherited through succeeding generations is demonstrated by
the fact that the effect persists even when the original stimulus
is removed. If the environment gradually reverts to its original
nature, the modified organisms will continue to retain their
altered form for several generations, and then they too revert.
Thus the response
of the organism to direct environmental pressure is demonstrated.
Yet it is seen to be of such a nature that it retains its flexibility
and is therefore able to adjust in either direction to its own
advantage and pass on the adjustment to successive generations.
In this way the mechanism contributes to the fitness of the organism
without endangering it if the environmental pressure changes.
This type of modification which continues for a limited time
even when the stimulus which provoked it is removed has been
termed a dauermodification.
Such a mechanism
serves the dual purpose of preserving the line in its purity
and maintaining the species as such, while at the same time opening
the way for a form of adjustment that allows a particular species
to spread successfully into different habitats which it could
not otherwise occupy. The nuclear genes therefore preserve the
species as such: the plasmagenes preserve the local population
as a variety.
between the conventional Darwinian view of natural selection
and the view which is now beginning to crystallize, based on
plasmagenic inheritance of acquired modifications, is this: the
depended upon a process
of selective elimination of the unfit, whereas the latter
favours survival by inherited adaptation. Progress, identified
as increasingly successful adaptation, no longer becomes a ruthless
weeding out, but a demonstration of a sensitive mechanism specifically
designed to guarantee exactly the opposite result, namely, an
improvement in the chances of survival of every individual. It
is in some sense a reflection of the benevolence of the Creator
rather than of a pitiless eradication in the interests of efficiency
at all costs.
Copyright © 1988 Evelyn White. All
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The older view
of nature as ruthlessly efficient is therefore replaced by a
more generous view, which holds that any disadvantaged species
need not be eliminated but is provided with the means of contributing
to the greater fitness of its descendants. This is achieved by
passing on to these future generations the benefits of its own
response to the environment even though these were not overtly
expressed in its members at the time.
It is as though
the Lord has so designed the mechanism of inheritance in order
that the "kinds" of Genesis will not be destroyed or
blurred, while yet allowing modification which greatly increases
the range of climate, altitude, food resources, and so forth,
that the particular species can occupy. There are numerous illustrations
of this type of response among plants and animals; and there
are some striking illustrations of it for man himself.