and so appreciated Darwin’s thoughts about taxonomy. Consequently, Cohn realized
that bacteria, too, needed to be classified based upon their genealogy. He realized,
though, that using their forms would be insufficient to this purpose and there was a
need to examine their developmental processes and chemical features to determine
their descent. Pasteur had even commented that differentiation of bacteria could only
come through examinations of their physiological functions (Cohn 1875). Thus
Cohn began a 20-year effort to find these features.
Cohn’s work led him to believe that bacteria form a distinct group of life and that
they transmit stable characters to subsequent generations, though variations sometimes appear, as they do in all life. He thought their group best fit in the plant
kingdom with their closest relatives the Schizophyta (fission plants) or
Cyanophyceae (cyanobacteria). The isolation of pure cultures also led Cohn to
propose that bacteria could be classified into distinct species (Cohn 1875). His
ideas did not take hold at first as the idea that they were morphologically pliable in
nature was still strong.
Microbiology research in the mid-nineteenth century, with the exception of
Pasteur, was largely being conducted in Germany (Matta 2007). Mattias Jakob
Schleiden was a botanist at the University of Jena and wrote in 1838 that plants
were made of cells and argued that botanists should focus on the functions of plant
cells, rather than their gross parts, to understand the nature of plants (Schleiden
1838). Cohn accepted this call, though, in doing so, his work disputed some of the
work of Schleiden (Drews 1999). Schleiden was early to accept Darwin’s theory of
evolution. Schleiden advocated for the study of cryptogams, plants without true
seeds and flowers like mosses, algae, and fungi, since they would allow easier
investigations of the basic processes of plants. This approach naturally included
examinations of microbes, including bacteria. Thus microbiological studies developed among botanists. A separate line of microbiological investigations arose among
medical practitioners, particularly after the work of the physician Koch. It was,
however, the work of botanical microbiology that focused on the functions of
microbes that led to interest in their place in the world and their evolution. Evolutionary questions were a natural part of botanical studies, but not those of investigators interested in medical aspects of microbes. Consequently, as the latter gained
greater influence over the science of microbiology after the turn of the twentieth
century, microbial evolution studies entered their “Dark Ages” as described below.
2.6 Early Attempts at a Natural Taxonomy of Bacteria
Cohn had also developed the idea of the cycle of life as applied to bacteria. In 1872
he described the “entire arrangement of nature” in which the decomposition of dead
material by microbes provided the materials for new life (Ackert Jr 2007). This,
along with Pasteur’s examinations of microbial ferments, began examinations of the
biochemical physiology of microorganisms and their contributions to the functioning of the planet.
2 Darwin’s Science’s Impact on the Evolution of the Microbiological Sciences
27
that bacteria, too, needed to be classified based upon their genealogy. He realized,
though, that using their forms would be insufficient to this purpose and there was a
need to examine their developmental processes and chemical features to determine
their descent. Pasteur had even commented that differentiation of bacteria could only
come through examinations of their physiological functions (Cohn 1875). Thus
Cohn began a 20-year effort to find these features.
Cohn’s work led him to believe that bacteria form a distinct group of life and that
they transmit stable characters to subsequent generations, though variations sometimes appear, as they do in all life. He thought their group best fit in the plant
kingdom with their closest relatives the Schizophyta (fission plants) or
Cyanophyceae (cyanobacteria). The isolation of pure cultures also led Cohn to
propose that bacteria could be classified into distinct species (Cohn 1875). His
ideas did not take hold at first as the idea that they were morphologically pliable in
nature was still strong.
Microbiology research in the mid-nineteenth century, with the exception of
Pasteur, was largely being conducted in Germany (Matta 2007). Mattias Jakob
Schleiden was a botanist at the University of Jena and wrote in 1838 that plants
were made of cells and argued that botanists should focus on the functions of plant
cells, rather than their gross parts, to understand the nature of plants (Schleiden
1838). Cohn accepted this call, though, in doing so, his work disputed some of the
work of Schleiden (Drews 1999). Schleiden was early to accept Darwin’s theory of
evolution. Schleiden advocated for the study of cryptogams, plants without true
seeds and flowers like mosses, algae, and fungi, since they would allow easier
investigations of the basic processes of plants. This approach naturally included
examinations of microbes, including bacteria. Thus microbiological studies developed among botanists. A separate line of microbiological investigations arose among
medical practitioners, particularly after the work of the physician Koch. It was,
however, the work of botanical microbiology that focused on the functions of
microbes that led to interest in their place in the world and their evolution. Evolutionary questions were a natural part of botanical studies, but not those of investigators interested in medical aspects of microbes. Consequently, as the latter gained
greater influence over the science of microbiology after the turn of the twentieth
century, microbial evolution studies entered their “Dark Ages” as described below.
2.6 Early Attempts at a Natural Taxonomy of Bacteria
Cohn had also developed the idea of the cycle of life as applied to bacteria. In 1872
he described the “entire arrangement of nature” in which the decomposition of dead
material by microbes provided the materials for new life (Ackert Jr 2007). This,
along with Pasteur’s examinations of microbial ferments, began examinations of the
biochemical physiology of microorganisms and their contributions to the functioning of the planet.
2 Darwin’s Science’s Impact on the Evolution of the Microbiological Sciences
27