THE FRONTIERS OF EVOLUTIONARY BIOLOGY

Everyone knows that our understanding of this world is still incomplete, in spite of the magnificent advances of science. We must ask ourselves, therefore, to what extent this is also true of evolutionary biology.

Here it must be emphasized that the development of molecular biology has resulted in an enormous increase of interest in and understanding of evolution. Easily one-third, if not more, of all papers now published in molecular biology deal with evolutionary questions. Molecular techniques allow us to solve numerous problems that had previously been inaccessible. This is particularly true for phylogenetic problems, for issues in the chronology of evolution, and for the role of development in evolution.

When we look back over the controversies of the last 140 years, what is most impressive is the robustness of the original Darwinian paradigm. The three major theories that competed with it—transmutationism, Lamarckism, and orthogenesis—were decisively refuted by about 1940, and no viable alternative to Darwinism has been proposed in the last 60 years. But this does not mean that we possess a full understanding of all aspects of evolution. I shall now try to enumerate a number of evolutionary phenomena in need of further research and explanation.

To begin with, we still have only a very incomplete knowledge of biodiversity. Although nearly two million animals have already been described, estimates of the number of still undescribed species go as high as 30 million. Fungi, lower plants, protists, and prokaryotes are even more poorly known. The phylogenetic relationship of most of these taxa are only poorly understood or entirely unknown, although molecular methods now make daily new contributions to this understanding. The fossil record of past evolution is still woefully inadequate, as illustrated by the hominid fossil record. Almost every month some new fossil is found somewhere in the world that solves an old problem, or poses a new one. And the ups and downs of the former biota raise innumerable questions about the causes of mass extinction and the varying fates of different phyletic lineages and higher taxa. Even at this rather descriptive level, our ignorance is still enormous. But there are also many uncertainties about aspects of evolutionary theory.

Even though there is no doubt as to the prevalence of geographic (allopatric) speciation and (in plants) polyploidy as the prevailing forms of speciation, we are still uncertain about the frequency of other forms of speciation, for instance, sympatric speciation. The contribution of various factors to the extraordinary rapidity (less than 10,000 or even 1,000 years) of speciation in certain groups of fishes is still not understood.

The astonishing slowdown or stasis of certain evolutionary lineages (“living fossils”) is also rather puzzling, considering that all the other members of their biota evolved at normal rates. The opposite extreme, the rapidity with which certain genotypes were restructured in founder populations, is likewise puzzling.

All of these puzzling problems ultimately seem to be due to the structure of the genotype. Molecular biology has discovered that there is a variety of kinds of genes, some in charge of the production of certain materials (enzymes), others involved in the regulation of the activity of other genes. Most genes apparently are not continuously active but only in certain cells (tissues) and at certain times in the life cycle. Other genes seem to be neutral, while an amazingly large proportion of DNA seems to be totally inactive. The genes of the genotype, therefore, form a complex system of interactions. Owing to these multiple interactions among all the composing genes, such a system is highly constrained. It can respond to some influences or environmental pressures, though most would lead to unbalances and will be selected against.

There are suggestions that genotypes were less tightly constrained at the beginning of the existence of the Metazoa so that for 200–300 million years in the late Precambrian or early Cambrian no fewer than 70 or 80 new structural types evolved. Only about 35 are now left, none of which has changed drastically (in the basics of their body plan) in the 500 million years since the Cambrian. How can we explain such a seemingly drastic change in evolutionary rate? Within these surviving structural types, however, there have been remarkable radiations, such as the insects and the vertebrates.

THE USEFULNESS OF EVOLUTIONARY THOUGHT

Evolutionary thought, and in particular an understanding of the new concepts developed in evolutionary biology, such as population, biological species, coevolution, adaptation, and competition, is indispensable for most human activities. We apply evolutionary thinking and evolutionary models to cope with antibiotic resistance by pathogens, pesticide resistance by crop pests, the control of disease vectors (e.g., malaria mosquitoes), human epidemics, the production of new crop plants by evolutionary genetics, and many more challenges (Futuyma 1998: 6–9).

The principal reason why scientists study evolution is to further our understanding of this phenomenon that affects every aspect of the living world. But evolutionary studies have also made many important contributions to human welfare. Evolutionary thinking has enormously enriched almost all other branches of biology. For instance, more than a third of all current publications in molecular biology show how the nature and history of important biological molecules are illuminated by an evolutionary approach. Developmental biology has been completely revitalized by the study of evolutionary questions and the establishment of the different categories of genes and their elaboration in the course of phylogeny. The evolutionary approach has also given us a wonderful insight into the history of mankind. And nothing has contributed more to our understanding of such human characteristics as mind, consciousness, altruism, character traits, and emotion than comparative studies of the behavior of animals.

It must never be forgotten that the genotype is a harmonious, interacting system that is exposed to natural selection as a whole. Whenever it is inferior in competition with some other genotype it will be selected against, a process that may lead to the extinction of the inferior species.

Biology also tries to explain three other complex systems: the developmental system, the neurosystem, and the ecosystem. Three major biological disciplines are occupied with this task. The study of the developmental system is the task of developmental biology; that of the neurosystem (central nervous system) is the task of neurobiology; and that of the ecosystem is the purview of ecology. However, in all three cases, it is the structure of the genotype that is ultimately responsible for how organisms can meet the challenges of these three systems. Our knowledge of the underlying building blocks of all three systems is already well advanced. Where we are deficient in explanations is the control of the interactions of the components of these systems. No doubt evolutionary biology will make major contributions toward this end.