ANSC 420 Lecture Notes - Rudolf Virchow, Jan Swammerdam, Infusoria

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A few lensmakers and natural philosophers had been creating crude microscopes since the late
16th century, and Robert Hooke published the seminal Micrographiabased on observations with
his own compound microscope in 1665. But it was not until Antony van
Leeuwenhoek's dramatic improvements in lensmaking beginning in the 1670sultimately
producing up to 200-fold magnification with a single lensthat scholars
discovered spermatozoa, bacteria, infusoria and the sheer strangeness and diversity of
microscopic life. Similar investigations by Jan Swammerdam led to new interest
in entomology and built the basic techniques of microscopic dissection and staining
Debate over the flood described in the Bible catalyzed the development of paleontology; in
1669 Nicholas Steno published an essay on how the remains of living organisms could be
trapped in layers of sediment and mineralized to produce fossils. Although Steno's ideas about
fossilization were well known and much debated among natural philosophers, an organic origin
for all fossils would not be accepted by all naturalists until the end of the 18th century due to
philosophical and theological debate about issues such as the age of the earth and extinction
Advances in microscopy also had a profound impact on biological thinking. In the early 19th
century, a number of biologists pointed to the central importance of the cell. In 1838 and
1839, Schleiden and Schwann began promoting the ideas that (1) the basic unit of organisms is
the cell and (2) that individual cells have all the characteristics of life, though they opposed the
idea that (3) all cells come from the division of other cells. Thanks to the work of Robert
Remak and Rudolf Virchow, however, by the 1860s most biologists accepted all three tenets of
what came to be known as cell theory.
Up through the 19th century, the scope of zoology was largely divided between physiology,
which investigated questions of form and function, and natural history, which was concerned
with the diversity of life and interactions among different forms of life and between life and non-
life. By 1900, much of these domains overlapped, while natural history (and its
counterpart natural philosophy) had largely given way to more specialized scientific
disciplinescytology, bacteriology, morphology,embryology, geography, and geology.
Widespread travel by naturalists in the early-to-mid-19th century resulted in a wealth of new
information about the diversity and distribution of living organisms. Of particular importance
was the work of Alexander von Humboldt, which analyzed the relationship between organisms
and their environment (i.e., the domain of natural history) using the quantitative approaches
of natural philosophy (i.e., physics and chemistry). Humboldt's work laid the foundations
of biogeography and inspired several generations of scientists.
The emerging discipline of geology also brought natural history and natural philosophy closer
together; Georges Cuvier and others made great strides in comparative
anatomy and paleontology in the late 1790s and early 19th century. In a series of lectures and
papers that made detailed comparisons between living mammals and fossil remains Cuvier was
able to establish that the fossils were remains of species that had become extinctrather than
being remains of species still alive elsewhere in the world, as had been widely believed. Fossils
discovered and described by Gideon Mantell, William Buckland, Mary Anning, and Richard
Owen among others helped establish that there had been an 'age of reptiles' that had preceded
even the prehistoric mammals. These discoveries captured the public imagination and focused
attention on the history of life on earth.
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