Janus (30 page)

 

 

While it was thus impossible to
disprove
either the Darwinian or the
Lamarckian theory by experiment, it turned out to be equally impossible
to
prove
either of them. On the Lamarckian side, the great Pavlov in
Leningrad and MacDougall at Harvard attempted to show that the results
of conditioning in mice and rats were inherited -- and failed to do so.*
On the other hand, the patient labours of the Darwinian geneticists on
thousands of generations of Drosophila have also failed to produce any
evolutionary improvement. As far as the direct experimental evidence is
concerned, the two sides might have called it quits.

 

* Perhaps closest to such proof came Karnmerer's controversial
experiments, described in The Case of the Midwife Toad
and J. McConnell's experiments on Planaria. [8]

 

If the neo-Darwinians nevertheless carried the day -- for the time being
-- the reason was, apart from metaphysical bias, that they were apparently
able to offer 'modern', scientific explanations of some aspects of the
evolutionary process, which the Lamarckians were unable to do. The discovery
of Mendel's laws, the statistical approach to genetics, and lastly the
'breaking of the genetic code', each looked at first like an added
confirmation of Darwin's prophetic foresight (forgetting his own lapses
into Lamarckism). The mechanism of evolution which he had proposed
may have been crude, in need of modifications and refinements; but
the Lamarckians could not offer any mechanism at all in keeping with
modern biochemistry. Random mutations in the chromosomes, triggered
by radioactivity or noxious chemicals, were prima facie scientifically
acceptable as a base for natural selection. But no acceptable hypothesis
was forthcoming to explain how an acquired bodily or mental feature
could alter the 'genetic blueprint', contained in the micro-structure
of the chromosomes. So once more the principle prevailed that a bad
theory is better than no theory, and Lamarckism acquired the stigma of a
'disreputable superstition' because it postulated a principle in nature
without being able to offer a mechanism, in terms of contemporary science,
to account for it.

 

 

This situation, however, has many precedents in the history of science.
When Kepler suggested that the tides were caused by the attraction
of the moon, even Galileo dismissed the idea as an 'occult fancy'
because there was no conceivable mechanism which could explain
action-at-a-distance. Later on, some of Newton's most eminent
contemporaries rejected universal gravity because it meant, in his
own words, 'grappling with ghost fingers at distant objects' and thus
contradicted the laws of mechanics.
Mutatis mutandum
, Lamarckism
was rejected because the proposition that the experiences acquired by
the living organism could influence the structure of its hereditary
chromosomes contradicted the laws of genetics summed up in the 'central
dogma'.

 

 

In actual fact the central dogma succumbed in less than twenty years
after its proclamation under the weight of rapidly accumulating new
evidence. On 25 June 1970, the
New Scientist
(which does not go in
for sensational headlines) announced: 'Biology's Central Dogma Turned
Topsy-Turvy' and
The Times
Science Report followed suit: 'Big Reverse
for Dogma of Biology'.
^[9]
The experimental work, which overturned
the central dogma (and which six years later was rewarded by a Nobel
Prize)* is too technical to be detailed here; suffice it to say that
it established beyond dispute that in certain bacteria the 'hereditary
blueprint' can be altered by the incorporation of agents of external
origin (viruses), which may have harmful or benign effects.
^[10]
Or, as Grassé summed it up:

 

These results demonstrate that there exists a molecular mechanism
which, in certain circumstances, supplies information from outside
to the organism and inserts this information into the organism's
genetic code. This is of immense importance to evolutionists."
* Shared by Temin, Baltimore and Dulbecco

 

It is indeed. This is why I called molecular genetics a Trojan Horse
inside the citadel.

 

 

It would, of course, be silly to jump to the conclusion that because
viruses can produce hereditary changes in a cell, therefore continued
piano practice by the parents will make them beget musical prodigies.
Nevertheless, the discoveries of molecular genetics in the course of
the last decade have finally demolished Weismann's doctrine of the
'unalterability of the germ-tract' and modified its modern version,
the 'central dogma'. Taken in conjunction with the criticisms discussed
earlier on, they may signal the beginning of the end of neo-Darwinism
as represented in contemporary textbooks. Darwinian selection no doubt
plays a part in the evolutionary process, but only a subordinate part
(comparable to the action of the selective weedkiller) and there is a
growing realization that there must be other principles and forces at
work on the vast canvas of evolutionary phenomena. In other words, the
evidence indicates that evolution is the combined result of a whole range
of causative factors -- some known, others dimly guessed, yet others so
far completely unknown.

 

 

 

4

 

 

In
The Case of the Midwife Toad
I suggested that within that wide
range of causative factors a 'modest niche might be found for a kind
of modified "mini-Lamarckism" as an explanation for some limited and
rare evolutionary phenomena'.
^[12]
In the light of recent
developments I am no longer sure that the niche must be so modest,
and the phenomena so rare. It would of course be absurd to revert to
the naive version of Lamarckism which Darwin himself embraced. As said
before, Lamarckism only makes sense if the inheritability of acquired
characteristics is confined to such bodily features and skills which
organisms acquire in response to persistent pressures and challenges of
the environment over many generations.

 

 

This limitation is essential, and the reasons for it can be explained
by a simple analogy. Our sense organs for sight and hearing act like
narrow slits or filters which admit only a very limited frequency range
of electro-magnetic and sound waves. But even this reduced input is
too much for us to cope with. Our minds would cease to function if we
bad to attend to each of the millions of stimuli which -- in William
James's classic phrase -- constantly bombard our receptor organs in a
'blooming, buzzing confusion'. Thus the nervous system and the brain
itself function as a multilevelled hierarchy of filtering and classifying
devices, which eliminate a large proportion of the input as irrelevant
'noise', and assemble the relevant information into coherent patterns
before it is presented to consciousness.* A typical example of this
filtering-and-synthesizing process is what psychologists call the
'cocktail-party phenomenon' -- our remarkable ability to isolate and
attend to a single voice from the medley of sounds impinging on the
ear-drum.

 

* Cf. Ch. I, 13.

 

Now what the Weismann doctrine, or the central dogma, really amounts to
is the postulate that a comparable filtering apparatus must protect the
hereditary blueprint in the germ-cells against the 'buzzing confusion'
of biochemical intrusions which otherwise would play havoc with the
continuity and stability of the species. But that does not necessarily
exclude the possibility that some very persistent and vital acquisitions,
made by generation after generation, may not gradually seep through the
filter and become hereditary. There are, at any rate, some classical
examples, quoted over and over again in the literature, which seem to
cry out for a Lamarckian explanation because Darwinism has none to offer:

 

There is, for example, the hoary problem why the skin on the soles of
our feet is so much thicker than elsewhere. If the thickening occurred
after birth, as a result of pressure and friction, there would be
no problem. But the skin of the sole is already thickened in the
embryo which has never walked, bare-foot or otherwise. A similar,
even more striking phenomenon are the horny callosities on the African
warthog's forelimbs, on which the animal leans while feeding; on the
knees of camels; and, oddest of all, the two bulbous thickenings on
the ostrich's undercarriage, one fore, one aft, on which that ungainly
bird squats. All these callosities make their appearance, as the
skin on our feet does, in the embryo. They are inherited
characteristics. But is it conceivable that these callosities
should have evolved by chance mutations just exactly where the animal
needed them? Or must we assume that there is a causal, Lamarckian
connection between the animal's need to protect these vulnerable
spots and the genetic mutation which satisfies that need? [13]

 

These examples, and many others which are too technical to be cited here,
have been bandied about by Lamarckians ever since the controversy started;
and the Darwinians, unable to offer a satisfactory explanation, consistently
evaded the issue, or -- on Samuel Butler's phrase -- kept 'ostrichizing'
the evidence. A century after Butler, these evasive tactics still prevail.*

 

* The interested reader will find a recent example of it in the
discussion which took place at the Alpbach Symposium after Professor
Waddingtons paper 'The Theory of Evolution Today', when the hoary
tale of the ostrich and the warthog was brought up again by the
present writer. [16]  It was particularly interesting to note
that although Waddington was, as we have seen, highly critical of
the synthetic theory, he instantly rallied to its defence when it
was attacked from outside.

 

It is admittedly difficult to see how an acquired callosity could
conceivably produce a change in the chromosomes. But, as Waddington
himself pointed out in an earlier book
^[14]
, 'even if improbable,
such processes would not be theoretically inexplicable. It must be for
experiment to decide whether they happen or not'. He even produced a
'speculative model' to show a possible way how changes in the activities
of body-cells could affect the gene-activities in germ-cells by means of
adaptive enzymes. As he wrote, the model was 'intended only to suggest
that it may be unsafe to consider that the occurrence of directed
non-random mutations related to the environment can be ruled out of
court
a priori
'.
^[15]

 

 

 

5

 

 

It has been known for a long time that the 'Weismann barrier' which
supposedly isolates the reproductive cells, the carriers of heredity,
from the rest of the body, does not apply to plants; nor to lowly animals
such as flatworms and hydra, which can regenerate a whole individual,
including its reproductive organs, from virtually any segment of their
bodies. Ultimately, biologists will have to face the choice of clinging
to the dogma of the 'impenetrable wall' protecting the 'unalterable
germ-tract' from the rest of the world, and ascribing all evolutionary
alterations of it to pure chance -- or admitting that the wall is
porous, a system of fine-meshed filters which permits only selected,
vital information to penetrate into the inner sanctum of heredity
in the germ-cells. Molecular genetics does not tell us -- as yet --
how this is achieved; but it is a new science in constant flux and it
does not exclude a priori the possibility of a phylogenetic memory for
vital and recurrent experiences encoded in the chromosomes. How else
but through some process of phylogenetic learning and memory-formation
could the complex inherited skills of building a bird's nest or weaving
a spider's web have arisen? The official theory, as we have seen, has
no explanation for the genetics of such inherited virtuosity.

 

 

To recapitulate: one can draw an analogy between the filtering apparatus
which operates in the nervous system to protect the mind from irrelevant
stimuli, and the genetic micro-hierarchy which protects the hereditary
endowment against harmful chance mutations, and coordinates the effects of
useful ones. We can now extend the analogy and suggest that there is also
a Lamarckian micro-hierarchy at work in the process of evolution, which
prevents acquired characteristics from interfering with the hereditary
blueprint -- except for those select few which respond to some vital need
of the species, originating in sustained pressures by the environment
over many generations -- like the thickened skin on the soles of the
human embryo. We would thus have a quasi-Darwinian micro-hierarchy,
mainly responsible for the immensely rich
variations
on the same level
of the evolutionary ladder, and a quasi-Lamarckian micro-hierarchy,
mainly responsible for the
evolution
to higher levels. And there are no
doubt still other causative factors at work, beyond our present horizon.

 

 

Only a fool could deny the revolutionary impact of Darwinism on the
outlook of the nineteenth century, when -- as one biologist put it,
^[17]
the educated public was faced with the alternative
'for Darwin or against evolution'. But the narrow sectarianism of the
neo-Darwinists of our own age is an altogether different matter; and
in the not-too-distant future biologists may well wonder what kind of
benightedness it was that held their elders in its thrall. This prognosis
is shared by some of the critics I have quoted, and perhaps by the
majority of the younger generation. It is certainly significant that even
in the Introduction, written by an eminent entomologist, to the Everyman
Library's Centenary Edition of Darwin's
The Origin of Species