9 months ago


converted into harmless

converted into harmless recessives by natural selection. When evolution was not in progress, natural selection made on the whole for uniformity. Polymorphism, the occurrence of a stable pattern of genetic inequality within populations, was recognised as an interesting but somewhat unusual phenomenon, each example of which required an explanation peculiar to itself. These ideas were superseded through the impact of genetics, which was far from departmental status in the universities of the 1920's. Natural populations are now known to be highly diverse, and even chemical polymorphism has been found wherever it has been looked for. Today it is no longer possible to think of the evolutionary process as the formulation of a new genotype or the inception of a new type of organism. The raw material of evolution is itself a diverse population, and the product is a new and well-adapted pattern of genetic inequality, shaped and actively maintained by selective forces. An important modern viewpoint is that the population, as a whole breeds true, not its individual members, so that we can no longer draw the old distinction between an active process of evolution and a more or less stationary end product. Evolution is constantly in progress and the genetical structure of every population is diverse and dynamically sustained. As yet, nothing is known about the genetic specification of order at levels above the molecular level, and this is probably where the next major developments in systematic zoology will occur. Already, it is possible to observe new ideas on the relationship between cellular and organ function emerging at the interface between developmental biology and cell biology, which may allow new insight into the way in which organs exist as integrated cellular systems in their own right. Cell biology had its origins in the two decades before the second World War coincidentally with the rise of biochemistry. Urease and pepsin were crystallised respectively in 1926 and 1930. Tobacco mosaic virus was crystallised in the 1930's, when it was thought to be a pure protein. Other portentous discoveries were those arising from X-ray diffraction, which revealed an essentially crystalline orderliness in common biological structures. The first electron micrographs were published in the 1930's with a resolving power of one micron. This was the time at which the old concept of the colloidal organisation of matter was being replaced by ideas of precise compartmentation of cells. The view of protoplasm as a fragile colloidal slime, permeating otherwise inanimate structures was already obsolete in the 12

thirties, but the colloidal conception was still used with an allowance made for heterogeneity, and for the existence of what were termed liquid-crystalline states and cytoskeletons. The substitution of the structural for the vague colloidal conception of the physical basis of life was one of the great revolutions of modern biology. The change was very gradual, and was only finally completed in the late 1950's when the electron microscope became a routine instrument. One of the most recent developments of the electron microscope enables chemical analysis to be carried out with a high degree of precision within the sectioned specimen. With this instrument, the biochemist and the zoologist may realise the long-sought integrative goal of their respective disciplines as they sit, side by side and discuss the implications of molecular events in a multi-molecular, highly compartmented structure. Biochemists, by destroying this compartmentation, destroy the regulating systems which they wish to study, and so can only study the 'nuts and bolts' of the organism. Other important interactions between biochemistry and zoology are now widespread at the physiological level. Although comparative studies of function have always taken place alongside anatomical investigations, it was in an effort to escape from the fruitless arguments of descriptive systematic zoology that a group of zoologists deliberately broke away from this mainstream in the 1920's in order to augment description by experiment. Two aspects of this new school of experimental zoology can be observed in modern zoology encompassed by the fields of comparative endocrinology and comparative neurophysiology. At worst, the experimental school has carried through a systematic philosophy to a less complex level of physiology and biochemistry without adding anything new to a phylogeny already established on morphological grounds. At best, it has unravelled the workings of new organ systems. This is particularly true for the structure and functions concerned with homeostasis or self-regulation, which was a concept clarified in the 1920's from many old ideas concerning the immediate resistance of animals to environmental change. Some of the greatest achievements of physiological analysis have been performed on material that in 1926 was known only to zoologists, but the exploitation of these structures, such as the giant axon of the squid, has been in the hands of workers trained in other fields. This probably reflects different attitudes towards biological modelling, where a system is chosen for study simply on the grounds that it shows in an exaggerated or uncomplicated form a mechanistic phenomenon of particular interest. Biological modelling is commonplace in physiology and biochemistry but not in zoology, where there is a tendency to study a particular animal long 13

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