There
are now a small but growing number of biologists who are questioning one of the
cornerstones of neo-Darwinism. These doubts centre on the important concept of the copying error or
the random mutation. According to neo-Darwinism, copying errors supply the raw
material on which the well-understood mechanism of natural selection can act.
The reliance on the copying error as the source of evolutionary novelty or
variation has long formed the basis of the arguments against Darwin's Theory
and it allows groups such as Christian fundamentalists to increasingly voice
their objections to the currently accepted version of Evolutionary Theory.
Since
the publication of his book Evolution: a case of stating the obvious,
Derek Hough has laid out the logical arguments in favour of non-random
mutations. He has now re-worked his original publication to include
mathematical evidence for his theory and he has also added the latest ideas
surfacing from leading scientists and thinkers on evolutionary theory. His
revised work, now re-titled Evolution: from copying errors to
evolvability is currently available from Amazon (ISBN 978-1846241130).
Derek Hough’s thesis can be explained by following the key stages through which life’s genetic algorithm has passed since it first appeared, possibly four billion years ago. Each of the following stages (except the first) can be simulated and explored with the use of computerized genetic algorithms.
1. The origin of life. Inert chemicals happen upon self-replication.
2. Exponential growth in numbers soon leads to the ‘filling up’ of any initial space available to these primitive replicators.
3. Competition for survival leads to improved copying fidelity and differential fitness.
4. There will be a tendency for the early biosphere to automatically ‘condense’ into species. The creation of niches being driven by the elimination of ‘types’ or extinction in a knockout competition; a phenomenon well understood and explained by Darwin in On the Origin of Species.
5. Perfect copying fidelity would be a certain road to extinction. A species composed entirely of clones would soon be eliminated when faced with competition from any other species with the slightest advantage. Copying fidelity would now be selected against and regularly occurring copying errors that in any way create useful variety would be retained by natural selection and form the basis of a variety maintenance system. It is important at this stage to understand that Hough is talking about the retention of the mechanism for creating this useful variety and not the retention of the variety per se. Lynn Helena Caporale in her book Darwin in the Genome explores the possible genetics behind the evolution of the mechanism of variety-generation. [see note (i)]
6. The environment of each unit of inheritance is composed of all other units of inheritance. This environment is never stable. Each heritable unit is always faced with an endlessly varying or variable environment. With an environment that consists of a range of possibilities each species will maximise its fitness by maintaining an appropriate range of characteristics and skills. Genes that influence the outcome of reproduction will control the maintenance of this variety.
7. Design possibility is not unlimited and heritable units ‘learn’, in an algorithmic sense, that maintenance of variety around a specific, limited range of possibilities enhances the average survival chances of these units. There is an element of predictability in the large but essentially limited range of environmental variation, and life’s genetic algorithm ‘learns’ to predict some of this variation and each species can then cope better with the vicissitudes of a varying environment by maintaining an appropriate degree of variety, either in its gene pool or via regularly occurring relevant mutations. Our own immune system presents us with a model for understanding how a species can quickly adapt to an environmental challenge. The limit to design possibility is exemplified in the phenomenon of Convergence, which is clearly expounded in the book Life’s Solution by Simon Conway Morris. [see note (ii)]
8. At the same time as heritable units are maintaining variety, they are also co-operating with other heritable units. Working in teams has proved to be an advantage almost from day one, and these twin characteristics of co-operation and variety maintenance lead to the creation of unique combinations of sub-units. These new combinations of sub-units will lead to the creation of unique organisms, which, whilst not directly demanded by the environment, will survive if there is an available niche. Empty niches will rapidly be filled and convenient niches will become more rare. But the niche requiring sophistication and complexity beyond anything previously achieved will always be available and will always be sought out by this algorithmic search. Evolution can then be seen as a systematic search through the expanse of design possibility or Design Space. [see note (iii)]
Summary
One of the key points which investigators into evolutionary mechanisms must understand is that universal inherited characteristics of life such as the functioning of cells, sexual reproduction, multicellularity and the genetic code itself have all been created by evolution. The system of maintaining variety from one generation to the next as outlined above is just another such universal characteristic and it is maintained because of its usefulness to life as a whole. (www.evolvability.org). The genes for such characteristics are not subject to the same environmental scrutiny as the genes for creating the physical characteristics of an organism. Derek Hough has previously described his thesis as the theory of the self-developing genome. The idea that certain genes control the reproductive success of other genes has profound implications for evolution. It explains phenomena that sit uncomfortably with neo-Darwinism such as sexual reproduction and group selection, both of which seem to break the rule of selfish survival. The new theory also accounts for the rapid evolution of antibiotic resistance.
Natural selection will now exert a two-fold influence in order to maintain an appropriate level of variety within each species. It acts on genes that maintain the variety-generating system and it also acts on ‘body-building’ genes to eliminate designs that sit uncomfortably at the edge of the fitness landscape. Occasionally, however, organisms of novel design escape from the straightjacket of the niche and jump into a new niche with their own fitness landscape, thereby facilitating speciation and evolution. The self-developing genome encourages pre-adaptive moves in Design Space whilst speciation separates out these new designs from the parental species and therefore allows the self-developing genome to drive further differentiation. [see note (iv)]
A wonderful emergent consequence of variety maintenance at the level of the sub-unit is the constant search for evolutionary novelty and complexity at the level of the organism.
Notes
(i)
Darwin
was very much pre-occupied with the mystery of the origin of new variation. (www.darwinvsdawkins.com). He considered the problem very
carefully. He knew nothing of genes or the arithmetic of genetic
algorithms. The closest he
came to the idea of variety generation was his theory of ‘use and disuse’,
which, in simple terms, stated that, for example, if you did a lot of press-ups
in your lifetime then your offspring would inherit bigger biceps. The next
generation would then possess a new range of bicep potentiality (both in a
physiological and a hereditary sense) and biceps could go on getting bigger and
bigger down the generations (or smaller if you didn’t exercise them). Both
Darwin’s and Hough’s theories have similar outcomes although Hough’s theory
dispenses with the need for any information to pass from the soma (the body) to
the germline (the genes).
(ii)
Organisms,
and indeed any heritable units, do not exist in isolation. Organisms only exist
in the context of a niche. An organism and its niche only ever exist together:
they define each other. Life on earth can then be seen to constitute an
integrated system, an interrelated network in which each individual unit has an
intimate knowledge (in an algorithmic sense) of their particular niche, which
is composed of other individual units. This interdependence, which stretches
back billions of years, determines the current characteristics of each
organism. These characteristics have been determined by the coordinated action
between the organism’s own genes and the genes belonging to the constituents of
its niche. This relationship leaves each organism with a pre-programmed
knowledge of its niche, a knowledge that takes account of any environmental
variation that can be tracked and prepared for. Biological characteristics are
limited by the possibilities of the genetic code and it is this limitation,
coupled with the length of time that the organism and its niche have evolved
together in unison that has driven the evolution of variety maintaining
mechanisms as a contingency against a continually varying or variable niche.
Computer simulations are similarly restricted by their code and for this reason
they are ideally suited to model evolution.
(iii)
Darwin
was puzzled by the universal phenomenon of ‘correlated variation’. He was
convinced that there must be some underlying biological mechanism that
ensured that all the different parts of an organism were correlated with each
other. This correlation is well explained by Hough’s theory. Let’s take the
evolution of the giraffe as a simplistic example. A giraffe needs long legs to
reach the higher branches. It then needs a long neck to enable it to feed at
ground level. And it then needs a strong heart to pump blood to a much greater
height. According to Hough, variety will be maintained in each of these three
characteristics. Each population of giraffes will contain a range of leg
length, neck length and heart strength. But the really interesting evolution
happens when a single individual, by chance, has each of these characteristics
at the high end of the range, i.e. long legs, a long neck and a strong
heart. This combination of characteristics will then be selected over other
combinations. Rapid evolution, which is possible as a result of a variety
maintenance mechanism, backs up Darwin’s description of an organism’s
characteristics as being ‘plastic’.
The emergence of non-trivial complexity is more
difficult to see but can be studied with the use of computerized genetic
algorithms. A good example of this approach can be found at http://myxo.css.msu.edu/papers/nature2003/Nature03_Complex.pdf
(iv)
Under
this system, differentiation (or evolution) is facilitated by an abundant
availability of unoccupied niches, which can occur, for example, following a mass
extinction. The self-developing genome will also take advantage of any
relaxation in natural selection following a sudden change of environment. For
example, domestication of animals for farming or as pets often allows genes
that were once subject to tight natural selection pressures to become available
for re-working to create other novel characteristics along with their
corresponding new niches. There was obviously a plentiful supply of empty
niches 600 million years ago when the evolution of large-scale life forms
initially took off: to attribute the pre-Cambrian explosion to a fortuitous
series of copying errors is absurd.