BOOK REVIEW: EVOLUTION, THE TRIUMPH OF AN IDEA

Carl Zimmer, 2002. Published by W. Heinemann, London. 364 pp.

Carl Zimmer writes in detail of the early years of Charles Darwin, his study in Cambridge, his enthusiastic interest in the natural world and his desire to discover how this world worked. In 1831, at the age of 21, Darwin got an unprecedented chance to see the world at work—to participate in a five-year-long voyage around the world on the HMS “Beagle.” This voyage was undertaken to test clocks for the British Navy and draw detailed maps. Darwin’s position was to be a companion to the captain and to collect plants and animals encountered during a journey. Darwin’s family paid for the trip and then supported him financially for the rest of his life so that he could devote all his time and energy to being a naturalist and not be distracted by having to work for a living.

Apparently Darwin’s first thoughts that life on the Earth evolved appeared to him during the voyage. Back in England he started to collect scientific evidence to confirm his assumptions. This process took more than twenty years until his book “On the origin of species by means of natural selection or the preservation of the favored races in the struggle for life” (often named simply “The origin of species”) was published in 1859. The extraordinary fact is that the first printing of 1250 copies was sold out in one day.

EVOLUTION, THE TRIUMPH OF AN IDEA is a thrilling review of Darwin’s theory from the time of its publication until recent time and its striking influence on the development of science. The importance of Darwin’s book was not only in the revolutionary idea that life on the Earth evolved but also in explanations how this process works. Darwin collected and presented innumerable facts—scientific evidence—confirming his theory. Carl Zimmer traces how new scientific data confirming the theory of evolution were discovered during the last 150 years and provides numerous new facts taken from different branches of science. Readers will find many interesting evolution-related subjects in this book: putting dates to the history of life, atomic clocks, fossils, genes, mutations, heredity, evolving of species, examples of natural selections, the tree of life, abnormalities in animals, life explosions, extinctions and rebirth, co-evolution, evolutionary medicine, AIDS, the evolution of sex and sexual selection, the social roots of human evolution, inventing tools, the origin of language and modern humans and many others.

Variability of species, isolation of living populations and natural selection are the main processes in the theory of evolution, which naturalists can observe in populations of living organisms. Modern genetics and microbiology explain how these processes work.

Evolution is impossible without variability and mutation in genes is a natural cause of variability. Mutations are an alteration in genes of a cell and may be the result of accidents in the replication of genetic material or they may be induced by external factors. These mutations are transmitted to the organism’s offsping. “Some mutations are harmful in certain circumstances, but a surprising number have no effect one way or the other. These neitral changes pop up in different populations and linger, creating a variability that is far greater than anyone had previously imagined. All of this variability can be a good thing, evolutionary speaking, because if conditions change, a mutation neutral effects can become useful and be favored by natural selection. Variability is also the raw material for making new species.” All individuals in a population of living organisms are different to some degree; they are not identical. This is called individual variability, variability whithin a single population, which manifests itself in different size, shape, color and other qualities of its individuals. In molluscs, individual variability may be traced in the existence of different shell forms (variations) widely known to collectors. For example, in Cypaeidae the length of each individual shell follows the so-called law of normal statistical distribution with smooth grading between two extremities (the majority of individuals being in the center, as is demonstrated in human height variation).

If a population of molluscs is isolated from other populations of the same species, individuals in this isolated population are breeding only among themselves and their genetic profile will grow distinct from the other groups of individuals of this species. New mutations that crop up in the isolated population could be spread throug natural selection untill all the individuals in the group carried them. Being isolated the mutation can not spread to the other groups of the species. The isolated population would become more and more genetically distinct and some genes could turn out to be incompatible with the genes of molluscs of the same species outside their own population. This is geographical variation, which defines a difference between geogra- phically separated populations of the same species.

If isolation was complete and lasted long enough, these molluscs might lose the ability to interbreed with the other geographical variants of the species. A new species may evolve as a result of this process, although we still do not know how much time is necessary for an isolated population of molluscs to evolve as a new species.

The many mollusc populations, called subspecies, are known from different stages of a process of speciation.

Zimmer tells about difficulties the theory of evolution went through, how teaching of evolution even was prohibited in certain countries. Even to-day one can encounter some kind of opposition. For example, part of the scientific public still feels uneasy with recognizing subspecies in molluscs, for example, as if species of living organisms do not evolve but arise suddenly. They may accept “species or forms” but forms have no scientific status and are not recognized by the formal zoological nomenclature. Perhaps they feel that all species of living creatures, once created do not change with time, in spite of numerous scientific facts confirming the existence of subspecies as a transitional stage in the evolving species.

Examples confirming the influence of variability, isolation and natural selection are known in molluscs inhabiting the Red Sea and its most north-eastern part—the Gulf of Aqaba. The molluscan fauna of the Red Sea, which was isolated from the Indian Ocean in the past, differs from that of the Indian Ocean in the number of living species and their peculiarities. The same is true for the Gulf of Aqaba, which was, perhaps isolated from the rest of the Red Sea in the past and nowadays is partly isolated by the narrow passage, the Strait of Tiran.

Only 54% (26 out of 48 species) of Cypraeidae, 61% of Conidae, 58% of Ranellidae and 53% of Terebridae known in the entire Red Sea are living in the Gulf of Aqaba. Many populations living in the Gulf are different from those found in the Red Sea proper: 80% of Cypraeidae in the Gulf can be delimited as subspecies and 40% of them are limited in their distribution to the Gulf and near-by areas.

EVOLUTION, THE TRIUMPH OF AN IDEA is an interesting, richly illustrated book that makes one think again about the evolutionary theory as a confirmed scientific model explaining how our world evolved, exists and may continue develop in the future.

This review is first published in TRITON 8, September 2003.