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The Cancer Journal - Volume 6, Number 4 (July-August 1993)

editorial


Evolution theory from a new perspective



No doubt Darwin's evolution theory is the most important theory biology. It is simple, intuitively obvious and explains how life evolved from simple to complex individuals. Darwin's theory attempts to replace the theory of Creationism, whose interpretation of the diversity of species is based on the first chapter of Genesis in the Bible (1). These two theories explain the diversity of life from different angles. Creationists ask "Who is responsible for this phenomenon?" and "What is its purpose?", while Darwinists are interested in "What is its underlying nature?", and "How does it change?". Each theory has its merits. Today Darwinism seems more appealing since it stimulates thinking and breeds new theories.

In spite of its great appeal, it is obvious that Darwin's theory will soon be replaced by a better one, particularly since it leaves many basic questions on evolution unanswered. The theory is too narrow and simplistic. It explains evolution in terms of three independent factors:
1. Each living entity has a genetic memory that contains a blueprint of the organism that is manifested by its phenotype. The genetic memory and blueprint may change randomly in an unpredictable way, leading to a change of the phenotype.
2. Genetic memory is inherited.
3. Blueprint changes affect the chances of the individual to survive in the hostile environment. In fact, the environment "selects" the best fitting individuals.

These simple rules do not account for the complexity of the processes involved in the evolution of species. The genome is hit by many mutations and it is inconceivable that only a few contribute to the selection process. The environment is even more complex. Its selection of the fittest depends on a large number of features while Darwin's theory presumes that it can be accounted for by a small number of attributes. At best, evolution theory is a drastic simplification of a complex process and is barely adequate for describing what really goes on. Yet many biologists apply it to explain virtually everything. Some even believe in Universal Darwinism, regarding it as a corner stone of an Universal Life (2-4).

In view of these shortcomings one is tempted to search for a better theory to replace Darwinism. Fortunately, there is a conceptual model for describing evolution that is at least as powerful and convenient as Darwin's theory. Embryogenesis. Let embryogenesis be regarded as evolution of cells in the organism. Each cell division in the growing embryo creates a progeny which differs slightly from its ancestor. The process is known as differentiation and may be explained in a Darwinian way. The genome of the dividing ancestor is hit by somatic mutation which changes the phenotype of its progeny. The best fitting progeny is then selected by the organism while the rest are eliminated. Each division reduces the potential of a cell to differentiate into different cell forms. This process is known as determination and is most pronounced at birth.

Embryogenesis can be described in two ways, either as increasing differentiation, or as Darwinian evolution of cells. It is still impossible to distinguish between the two possibilities by experimental means. Both descriptions are equivalent in many aspects, e.g., embryological determination is analogous to Darwinian speciation. If so, why not explore the merit of the differentiation concept for explaining the variety of species? It seems that we might have some difficulty in doing so, since embryological differentiation proceeds in a sealed-off microcosm, while Darwinian evolution proceeds in the open. This apparent distinction may not be correct. In fact, what appears as Darwinian evolution of species could also be regarded as species differentiation proceeding within a super-individual called Gaia (5).

The name of the Greek Earth Goddess Gaia stands for a startling hypothesis by James Lovelock according to which "the biosphere is a self-regulating entity with the capacity to keep our planet healthy by controlling the chemical and physical environment". Gaia is an ecosystem which was born in the "primitive soup" and has been evolving, or differentiating, ever since. While the Biosphere is defined as the part of Earth where living things normally exist, Gaia is a biosphere which controls itself. An ecosystem in which Life and its environment are coupled. Gaia differentiates and the life forms differentiate in it.

The analogy between differentiation and Darwinian evolution is also highly relevant for understanding neoplasia (6,7). The oncological dogma maintains that a neoplasm is a parasite created during a chance mutation evolving according to Darwin's laws. Random mutations change the genome of the evolving neoplasm and the environment, here the host, selects the best fitting malignant cells (8). The current dogma thus implicitly assumes that the host actively selects and promotes its own destruction. Fortunately, differentiation provides a better explanation, and since it is equivalent to Darwinian evolution, neoplasia can be explained as differentiation. A neoplasm is regarded here as an organ created by the organism which differentiates for the host's own benefit (9).


G. Zajicek
e-mail: Gershom@md2.huji.ac.il


REFERENCES

1 Numbers RL. The Creationist: The Evolution of Scientific Creationism. Knopf, 1992
2 Dawkins, R. Universal biology Nature 360:25-26,1992
3 Estling R. Universal Darwinism. Nature 361,489,1993
4 Dover G. Universal Darwinism. Nature 360,505,1992
5 From Gaia to Selfish Genes. Barlow C. Editor The MIT Press Cambridge MA, 1991.
6 Zajicek G. What is a disease? Cancer J 4:296,1991.
7 Zajicek G. What is neoplasia? Cancer J 4:228,1991.
8 Nowell PC. The clonal evolution of tumor cell populations. Science, 194:23-28, 1976.
9 Zajicek G. Cancer is a metabolic deficiency. Cancer J 4:356, 1991.



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