Janus (28 page)

 

 

 

6

 

 

I have quoted some voices of dissent coming from biologists in eminent
academic positions. There have been many others, just as critical of the
orthodox doctrine, though not always as outspoken -- and their number is
steadily growing. Although these criticisms have made numerous breaches
in the walls, the citadel still stands -- mainly, as said before,
because nobody has a satisfactory alternative to offer. The history of
science shows that a well-established theory can take a lot of battering
and get itself into a tangle of contradictions -- the fourth phase of
'Crisis and Doubt' in the historic cycle* and yet still be upheld by the
establishment until a breakthrough occurs, initiating a new departure,
and the start of a new cycle.

 

* See above, Ch. VIII, 9.

 

But that event is not yet in sight. In the meantime, the educated public
continues to believe that Darwin has provided all the relevant answers
by the magic formula of random mutation plus natural selection -- quite
unaware of the fact that random mutations turned out to be irrelevant
and natural selection a tautology.

 

 

Towards the end of the last century Samuel Butler, another disenchanted
Darwinian, wrote in his
Notebooks
:

 

I attacked the foundations of morality in Erewhon, and nobody
cared two straws. I tore open the wounds of my Redeemer as he
hung upon the Cross in The Fair Haven, and people rather
liked it. But when I attacked Mr Darwin they were up in arms in a
moment. [44]

 

Nearly a century later, the emotional reactions to such
lèse
majesté
are still much the same.

 

 

 

7

 

 

In the 1950s a new popular symbol was added to Newton's apple and Mendel's
peas: the double helix. The unravelling of the chemical structure of DNA,
the nucleic acid in the chromosomes, carrier of the 'hereditary blueprint',
was in itself a remarkable achievement and focused attention on the new
field of molecular biology or molecular genetics. At first it looked --
as had been the case with Mendel's laws -- like a heavenly gift to
neo-Darwinism, but it soon turned out to be more of a Trojan horse: the
new insights gained into the infinitely complex bio-chemistry underlying
the 'strategy of the genes' finally demolished the naively simplistic
model of Mendelian genetics.

 

 

In the earlier versions of the model, the chromosomes were represented
as the keyboard of a grand piano with millions of keys.* The fertilized
egg had the whole keyboard at its disposal. As the embryo developed
and each cell became differentiated, most of its keyboard was sealed
off by 'scotch tape' and only those keys remained operative which
served the cell's specialized functions. The 'scotch tape' is called
in the language of genetics a 'repressor'. The agent which strikes
the key which activates the gene at the required time is an inducer or
'operator'. A mutated gene is a key which has got out of tune. On some
occasions, when quite a lot of keys have gone quite a lot out of tune,
the result, we were asked to believe, was a wonderful new melody --
a reptile transformed into a bird, or a monkey into a man.** Somewhere
along the line the theory had obviously gone wrong.

 

* See above, Ch. I, 9.
** This may sound like a malicious caricature of the theory.
However, I used this musical simile for the first time in The
Ghost in the Machine (1967) and three years later Monod himself
endorsed it, as it were: 'Even today,' he wrote [45], 'a good many
distinguished minds seem unable to accept or even to understand
that from a source of noise natural selection alone and unaided
could have drawn all the music of the biosphere.'
Another metaphor, approved by geneticists, compares mutations
(during replication of the chromosomes) to copying errors committed
by careless typists. [46]  Grassé commented: 'The monks of
the Middle Ages made copying errors which altered and corrupted
the texts which they had to reproduce. Who would dare to pretend
that these mistakes constitute the works?' [47]

 

The point where it went wrong was, as we have seen, the atomistic concept
of the gene. At the time when genetics got into its stride, the nineteenth-
century type of atomism was being abandoned by physicists, but was still
in full bloom in the life sciences: reflexes were atoms of behaviour,
and genes were atomic units of heredity. A certain gene was responsible
for straight or curly hair, another for haemophilia; and the organism
was represented as a mosaic composed of these elementary units. But by
the middle of our century these rigidly atomistic concepts of Mendelian
genetics had been considerably softened up -- and had actually become
fluid. It was realized that a single gene may affect a wide range of
different characteristics (pleiotropy). And vice versa, a great number of
genes may interact with each other to produce a single characteristic
(polygeny). Some trivial feature, such as the colour of the iris,
may depend on a single gene, but the hereditary configuration of all
important features of the organism depends on the totality of genes --
the gene complex or 'genome' as a whole. Thus by 1957 one could read
statements like the following in respectable biology textbooks:

 

All genes in the total inherited message tend to act together as an
integrated whole in the control of development . . . It is easy to
fall into the habit of thinking that an organism has a set number
of characteristics with one gene controlling each character. This
is quite incorrect. The experimental evidence indicates clearly that
genes never work altogether separately. Organisms are not patchworks
with one gene controlling each of the patches. They are integrated
wholes, whose development is controlled by the entire set of genes
acting co-operatively. [48]

 

This is a far cry from the earlier versions of the theory. In those
early days of genetics, a gene could be 'dominant' or 'recessive', and
that was about all there was to know about it. But with the advent of
molecular biology, phenomena of previously undreamt-of complexity entered
into the model (just as in sub-atomic physics), so that more and more
terms had to be coined and added to the vocabulary: repressor genes,
with co-repressors and apo-repressors; modifier genes, switch genes,
operator genes which activate other genes, 'cistrons' and 'operons'
(Monod) which constitute sub-systems of interacting genes (we might
call them 'genetic holons'), and even genes which regulate the rate
of mutations in genes. While the activities of the chromosomes had
originally been conceived like the unfolding of a linear sequence as
on a tape-recorder, it should have gradually become apparent that the
genetic controls in the cells of the developing embryo operate as a
self-regulating micro-hierarchy
, equipped with feedback devices from a
hierarchy of environments* which surrounds each and every cell.

 

* See above, Ch. I, 9.

 

Such a holarchy -- unlike a recording tape or a 'blueprint' -- must be
conceived of as a stable, flexible affair. Yet it must to a large extent
be self-regulating and capable of self-repair. It must not only protect
the growing embryo against the hazards and buffetings to which it is
exposed, but also protect the species against the evolutionary hazards of
phylogeny -- the random mutations occurring in its own chromosomal genes.

 

 

The conception of a 'genetic micro-hierarchy'* is still regarded with
scepticism or hostility among the hard core of the defenders of the
synthetic theory -- mainly, perhaps, because its acceptance would lead
to a basic revaluation of our notions of the evolutionary process --
as will be seen in subsequent chapters.

 

* A term first proposed, as far as I know, by L. L. Whyte.

 

 

8

 

 

Unlike the current metaphor of the 'genetic blueprint' which gives
the impression of a fixed topological map to be mechanically copied,
the concept of a 'genetic hierarchy' implies that the selective and
regulative controls in the organism operate on several levels.

 

 

The lowest levels are concerned with
eliminating
harmful variations
in the genetic material; the higher levels with
coordinating
the effects
of acceptable changes. The mystery, as we shall see, lies in the operation
of the higher levels -- the coordination (or orchestration) of those changes
which transform the amphibian egg into a reptilian egg, and a reptile into
a bird. But first, I must say a few words about the operation of the lower
levels.

 

 

Several biologists (among them von Bertalanffy, Darlington, Spurway,
Lima-de-Faria and, more recently, Monod) have suggested that the evolutionary
screening process -- the action of the 'selective weedkiller' -- might start
inside the organism, on the level of the molecular chemistry of the genome
itself. Mutations are alterations in the sequence of the chemical units in
the chromosomes (the four letters of the genetic alphabet); they have
been compared to the copying errors of mediaeval monks which corrupted
the antique texts.
^[49]
The concept of 'internal selection' launched
by the biologists just quoted, implies that there is a hierarchy of
correctors and proof readers at work to eliminate the misprints. In the
orthodox theory, natural selection is entirely governed by the pressures
of the
external
environment, which kills off the unfit and blesses
the fit with abundant progeny. In the light of the foregoing, however,
any chromosomal change, whatever its cause, must pass the tests of
internal
selection for physical, chemical and biological fitness
before being let loose as an evolutionary novelty. Thus the concept of
a genetic micro-hierarchy imposes strict limitations on the range and
evolutionary impact of random mutations and
reduces the importance of
the chance factor to a minimum
. The proverbial monkey at the typewriter
works in fact on a very sophisticated machine which the manufacturers have
programmed to print only words which convey meaning and to erase nonsense
syllables automatically.* Thus the hierarchic model at least enables us
to get rid of the monkey-typist and of Monod's roulette wheel. It does
not answer the ultimate question who or what programmed that prodigious
typewriter, but it puts the question mark where it properly belongs and
enables us to approach the problem step by step as we move on to higher
levels of the genetic hierarchy.

 

* This metaphor is almost literally applicable to mistakes made in
the protein manufacture in micro-organisms due to 'nonsense syllables'
appearing in the RNA. [50]

 

The next step leads us to the remarkable powers of regeneration and
self-healing which reside in the gene-complex as a whole, or a substantial
sub-assembly of it. These powers are demonstrated by experimental embryology;
we remember (p. 41) that if, in the early stages of development of the
newt embryo, the tissue which would normally develop into its tail, is
transplanted into the position of a future leg, that tissue will grow
not into a tail, but into a leg. Such magic is not confined to ontogeny;
it can also be observed in phylogeny. I have given one example among
many in
The Ghost in the Machine
:

 

The fruit-fly has a mutant gene which is recessive, i.e., when paired
with a normal gene, has no discernible effect . . . But if two of
these mutant genes are paired in the fertilized egg, the offspring
will be an eyeless fly. If now a pure stock of eyeless flies is made
to inbreed, then the whole stock will have only the 'eyeless' mutant
gene . . . Nevertheless, within a few generations, flies appear in
the inbred 'eyeless' stock with eyes that are perfectly normal.
The traditional explanation of this remarkable phenomenon is that
the other members of the gene-complex have been 'reshuffled and
re-combined in such a way that they deputise for the missing normal
eye-forming gene'. [51]

 

But no biologist has been so perverse as to suggest that the new eyes
evolved by pure chance, thus repeating in a few generations an evolutionary
process which took millions of years. Nor does the concept of natural
selection provide the slightest help. The re-combination of genes to
deputize for the missing gene must have been coordinated according to some
overall plan, or set of rules, governing the action of the gene-complex
as a whole. It is this coordinating activity, originating at the apex
of the genetic hierarchy which ensures
both
the genetic stability of
species over millions of years, and their evolutionary modifications
along biologically acceptable lines.
The central problem of evolutionary
theory is how this vital coordinating activity is carried out.
This is
where the big question mark comes in. The metaphor has shifted from the
croupier at the roulette wheel to the conductor directing his orchestra.

 

 

This shift was already foreshadowed by some of the founding fathers of
neo-Darwinism who became dissenters, such as Bateson and Johannsen. The
latter (who, we remember, coined the term 'gene') wrote that after all the
minute effects of Mendelian mutations had been taken into consideration,
there would still remain 'a gteat central something' which contained
the clue to the enigma. [52]

 

 

Waddington had an ambivalent attitude to the official theory; I have
quoted him poking fun at evolution-by-chance-mutation; on the other hand,
he wanted to avoid a complete break with the Darwinian doctrine. As a
way out of the dilemma, he proposed in a much-quoted broadcast lecture
that in the evolution of a complex organ, such as the human eye, a chance
mutation may 'affect the whole organ in a harmonious way'. This implies
that the mutation affecting a single component -- say, the lens -- acts
merely as a trigger on a complex pre-set system which has been programmed
to react 'in a harmonious way' (our 'programmed typewriter'); and that
this programming is also inherited, i.e., represented on a higher level
of the genetic hierarchy. Moreover, the harmonious evolution of seemingly
unrelated organs (i.e., the wings, air-sacs and digestive system of birds)
is coordinated at an even higher level -- the 'great central something'
at the apex of the hierarchy.