Cronologia delle maggiori scoperte
Certain key discoveries have greatly influenced progress in the study of zoology. This appendix presents some major landmarks in the development of biology and the individuals whose names are commonly associated with them. It is very difficult to appraise the historical development of any field of study. One investigator often gets the credit for an important discovery when many others should share in the prestige. No one individual has a monopoly on ideas; advances in science are built on the work of many minds. Especially in recent years, important discoveries have resulted from the efforts of teams of investigators. Furthermore, because knowledge of a topic accrues over a period of time, it is often difficult to decide in which year the "discovery" occurred.
In this brief outline the student may be able to see some relationships that exist between one discovery and another. Discoveries are not completely isolated, as they may sometimes appear. One may note also that fundamental discoveries in a particular branch of biology tend to be grouped fairly close together chronologically because that particular interest may have dominated the thought of biological investigators at that time.
A reader may wish to locate important discoveries in a given area without reading the entire list. Such an effort may be made easier by use of the following key symbols. Any such system of classification suffers some limitations, however. Many basic discoveries are not easily categorized because they have implications in wide areas. The list of categories must be short, or it becomes too cumbersome. Nevertheless, we hope that the classification will be useful.
[T] Taxonomy, systematics, and environmental fields (behavior, ecology, and the like)
[O] Tissue- and organ-level anatomy and physiology
[C] Cell biology
[D] Developmental biology
[G] Genetics
[E] Evolution and paleontology
[M] Of particular medical significance
Origins of Basic Concepts and Key Discoveries in Zoology
[O] circa 450-370 b.c.: Hippocrates. Establishment of the first biomedical tradition.
This Greek physician developed an extensive body of anatomical and physiological knowledge that formed the basis of the revival of research in anatomy and physiology in the Renaissance. He is best remembered as the "Father of Medicine" who devised the code of medical ethics now administered as an oath to beginning medical practitioners.
384-322 b.c.: Aristotle. The foundation of zoology as a science.
Although this pioneer zoologist and philosopher cannot be appraised by modern standards, there is scarcely a major subdivision of zoology to which he did not make some contribution. However, Aristotle was more a philosopher and poet than scientist, and much of his biological writing is riddled with erroneous opinion.
[O] 130-200 a.d.: Galen. Development of anatomy and physiology.
This Roman investigator has been praised for his clear concept of scientific methods and blamed for passing down certain glaring errors that persisted for centuries. His influence was so great that for centuries students considered him the final authority on anatomical and physiological subjects.
1347: William of Occam. Occam's razor.
This principle of science has received its name from the fact that it is supposed to cut out unnecessary and irrelevant hypotheses in the explanation of phenomena. The gist of the principle is that, of several possible explanations, the one that is simplest, has the fewest assumptions, and is most consistent with available data is the most probable.
[O] 1543: Vesalius, Andreas. First modern interpretation of anatomical structures.
With his insight into fundamental structure, Vesalius ushered in the dawn of modern biological investigation. Many aspects of his interpretation of anatomy are just now beginning to be appreciated.
[O] 1616-1628: Harvey, William. First accurate description of blood circulation.
Harvey's classic demonstration of blood circulation was the key experiment that laid the foundation of modern physiology. He explained bodily processes in physical terms, cleared away much of the mystical interpretation, and gave an auspicious start to experimental physiology.
[O] 1627: Aselli, G. First demonstration of lacteal vessels.
This discovery, coming at the same time as Harvey's great work, supplemented the discovery of circulation.
[O] 1649: Descartes, René. Early concept of reflex action.
Descartes postulated that impulses originating at the receptors of the body were carried to the central nervous system where they activated muscles and glands by what he called "reflection."
[D] 1651: Harvey, William. Aphorism of Harvey: Omne vivum ex ovo (all life from the egg).
Although Harvey's work as an embryologist is overshadowed by his demonstration of blood circulation, his De Generatione Animalium, published in 1651, contains many sound observations on embryological processes.
[O] 1652: Bartholin, Thomas. Discovery of lymphatic system.
The significance of the thoracic duct in its relation to the circulation was determined in this investigation.
[O] 1658: Swammerdam, Jan. Description of red blood corpuscles.
This discovery, together with Swammerdam's observations on the valves of the lymphatics and the alterations in shape of muscles during contraction, represented early advancements in the microscopical study of bodily structures.
[O] 1661: Malpighi, Marcello. Demonstration of capillary circulation.
By demonstrating capillaries in the lung of a frog, Malpighi was able to complete the scheme of blood circulation. Harvey never saw capillaries and thus never included them in his description.
[C] 1665: Hooke, Robert. Discovery of cells.
Hooke's investigations were made with cork, and the term "cell" fits cork much better than it does animal cells, but by tradition the misnomer has stuck.
[C] 1672: de Graaf, R. Description of ovarian follicles.
De Graaf's name is given to the mature ovarian follicle, but he believed that follicles were the actual ova, an error later corrected by von Baer.
[C][T] 1675-1680: van Leeuwenhoek, Anthony. Discovery of protozoa.
The discoveries of this eccentric Dutch microscopist revealed a whole new world of biology.
[T] 1693: Ray, J. Concept of species.
Although Ray's work on classification was later overshadowed by that of Linnaeus, Ray was really the first to apply the species concept to a particular kind of organism and to point out the variations that exist among the members of a species.
[O] 1733: Hales, Stephen. First measurement of blood pressure.
This was further proof that bodily processes could be measured quantitatively-more than a century after Harvey's momentous demonstration.
[D] 1745: Bonnet, Charles. Discovery of natural parthenogenesis.
Although somewhat unusual in nature, this phenomenon has yielded much information about meiosis and other cytological problems.
[T] 1758: Linnaeus, Carolus. Development of binomial nomenclature system of taxonomy.
So important is this work in taxonomy that 1758 is regarded as the starting point in the determination of generic and specific names of animals. Besides the value of his binomial system, Linnaeus gave taxonomists a valuable working model of conciseness and clearness that has never been surpassed.
[D] 1759: Wolff, Kaspar F. Embryological theory of epigenesis.
This embryologist, the greatest before von Baer, did much to overthrow the preformation theory then in vogue and, despite many shortcomings, laid the basis for the modern interpretation of embryology.
[O] 1760: Hunter, John. Development of comparative investigations of animal structure.
This vigorous eighteenth-century anatomist gave a powerful impetus not only to anatomical observations but also to establishment of natural history museums.
[T] 1763: Adanson, M. Concept of empirical taxonomy.
This botanist proposed a scheme of classification that grouped individuals into taxa according to shared characteristics. A species would have the maximum number of shared characteristics according to this scheme. The concept has been revived recently by exponents of numerical taxonomy. It lacks the evaluation of the evolutionary concept and has been criticized on this account.
[G] 1763: K?lreuter, J.G. Discovery of quantitative inheritance (multiple genes).
K?lreuter, a pioneer in plant hybridization, found that certain plant hybrids had characteristics more or less intermediate between the parents in the F1 generation, but in the F2 there were many gradations from one extreme to the other. An explanation was not forthcoming until after Mendel's laws were discovered.
[T] 1768-1779: Cook, James. Influence of geographical exploration on development of biology.
This famous sea captain made possible a greater range of biological knowledge because he took able naturalists on his voyages of discovery.
[C] 1772: Priestley, J., and J. Ingenhousz. Concept of photosynthesis.
These investigators first pointed out some major aspects of this important phenomenon, such as the use of light energy for converting carbon dioxide and water into released oxygen and retained carbon.
[C] 1774: Priestley, J. Discovery of oxygen.
Discovery of this element is of great biological interest because it helped in determining the nature of oxidation and the exact role of respiration in organisms.
[C] 1778: Lavoisier, Antoine L. Nature of animal respiration demonstrated.
A basis for the chemical interpretation of the life process was given a great impetus by the careful quantitative studies of the changes during breathing made by this great investigator. His work also meant the final overthrow of the mystical phlogiston hypothesis that had held sway for so long.
[T] 1781: Abildgaard, P. First experimental life cycle of a tapeworm.
Life cycles of parasites may be very complicated, involving several hosts. That a parasitic worm could require more than one host was a revolutionary concept in Abildgaard's day and was widely disbelieved until the work of Küchenmeister over 60 years later.
[E] 1791: Smith, William. Correlation between fossils and geological strata.
By observing that certain types of fossils were peculiar to particular strata, Smith was able to work out a method for estimating geological age. He laid the basis of stratigraphic geology.
[O] 1792: Galvani, L. Animal electricity.
The lively controversy between Galvani and Volta over the twitching of frog legs led to extensive investigation of precise methods of measuring various electrical phenomena of animals.
[E] 1796: Cuvier, Georges. Development of vertebrate paleontology.
Cuvier compared the structure of fossil forms with that of living ones and concluded that there had been a succession of organisms that had become extinct and were succeeded by the creation of new ones. To account for this extinction, Cuvier held to the theory of catastrophism, or the simultaneous extinction of animal populations by natural cataclysms.
[E] 1801: de Lamarck, J.B. Evolutionary concept of use and disuse.
Lamarck gave the first clear-cut expression of a hypothesis to account for organic evolution. His assumption was that acquired characteristics were inherited; modern evolutionists have refuted this part of the hypothesis.
[O] 1802: Young, T. Hypothesis of trichromatic color vision.
Young's hypothesis suggested that the retina contained three kinds of light-sensitive substances, each having a maximum sensitivity in a different region of the spectrum and each being transmitted separately to the brain. The three substances combined produced the colors of the environment. The three pigments responsible are located in three kinds of cones. Young's explanation has been modified in certain details by other investigators.
[O] 1811: Bell, C., and F. Magendie. Discovery of the functions of dorsal and ventral roots of spinal nerves.
This demonstration was a starting point for an anatomical and functional investigation of the most complex system in the body.
[D] 1817: Pander, C.H. First description of three germ layers.
The description of three germ layers was first made on chicks, and later the concept was extended by von Baer to include all vertebrates.
[D] 1827: von Baer, Karl. Discovery of mammalian ovum.
The very tiny ova of mammals escaped de Graaf's eyes, but von Baer brought mammalian reproduction into line with that of other animals by detecting ova and their true relation to follicles.
[C] 1828: Brown, Robert. Brownian movement first described.
This interesting phenomenon is characteristic of living matter and sheds some light on the structure of cells.
[T] 1828: Thompson, J.V. Nature of plankton.
Thompson's collections of these small forms with a tow net, together with his published descriptions, are the first records of the vast community of planktonic animals. He was also the first to work out the true nature of barnacles.
[C] 1828: W?hler, F. First to synthesize an organic compound.
NH2CONH2. This success in producing an organic substance synthetically was the stimulus that resulted in preparation of thousands of compounds by others.?W?hler succeeded in making urea (a compound formed in the body) from the inorganic substance ammonium cyanate; thus, NH4OCN
[D][E] 1830: von Baer, Karl. Biogenetic law formulated.
Von Baer's conception of this law was conservative and sounder in its implication than has been the case with many other biologists (Haeckel, for instance). Von Baer stated that embryos of higher and lower forms resemble each other more the earlier they are compared in their development, and not that the embryos of higher forms resemble the adults of lower organisms.
[E] 1830: Lyell, C. Modern concept of geology.
The influence of this concept not only did away with the catastrophic theory but also gave a logical interpretation of fossil life and the correlation between the formation of rock strata and the animal life that existed at the time these formations were laid down.
[C] 1831: Brown, Robert. First description of cell nucleus.
Others had seen nuclei, but Brown was the first to name the structure and to regard the nucleus as a general phenomenon. This description was an important preliminary to the formation of the cell theory a few years later, for Schleiden acknowledged the importance of the nucleus in the development of the cell concept.
[O] 1833: Hall, Marshall. Concept of reflex action.
Hall described the method by which a stimulus can produce a response independently of sensation or volition and coined the term "reflex action." It remained for the outstanding work of Sir Charles Sherrington in the twentieth century to explain much of the complex nature of reflexes.
[M][O] 1835: Bassi, Agostino. First demonstration of a microorganism as an infective agent.
Bassi's discovery that a certain disease of silkworms was caused by a small fungus represents the beginning of the germ theory of disease that was to prove so fruitful in the hands of Pasteur and other able investigators.
[C] 1835: Dujardin, Felix. Description of living matter (protoplasm).
Dujardin associated the jellylike substance that he found in protozoa and that he called "sarcode" with the life process. This substance was later called "protoplasm," and the sarcode idea may be considered a significant landmark in the development of the protoplasm concept.
[M][O] 1835: Owen, Richard. Discovery of Trichinella.
This versatile investigator is chiefly remembered for his researches in anatomy, but his discovery of this very common parasite in humans is an important landmark in the history of parasitology.
[C][O] 1838: von Liebig, Justus. Foundation of biochemistry.
The idea that vital activity could be explained by chemicophysical factors was an important concept for biological investigators studying the nature of life.