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: from copying errors to evolvability, Derek Hough has laid out the logical arguments in favour of non-random mutations. Written for students and the interested layperson, Derek Hough’s book introduces the reader to the important phenomenon of the algorithmic process, an understanding of which is vital to an understanding of evolution.
Berkeley Publishing has a limited number of copies of Hough’s book available to students, free-of-charge. Please email your mailing details to berkeleypub@aol.com
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
The essence of
Hough’s thesis is that it is not only organisms that are acted upon by
natural selection but more importantly natural selection also ensures that the
best systems for creating those
organisms are also selected. 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
(www.molinu.org/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.