Following a trip with Alexander von Humboldt through eastern Russia and the
Chinese frontier in 1829, Ehrenberg began a 30-year study of infusoria in soils,
sediments, rocks, and dust samples that he and others had collected from around the
world. He studied and named many species of protists and diatoms, in particular. He
attempted to associate different species with their geographic distribution. It was
these studies that attracted Darwin’s attention. Darwin thought that his samples
would help him extend his biogeographic studies to the microbial world. He also
thought that the microbiology of some of his rock samples would help him prove
how those sedimentary rocks formed. In particular, he was looking for proof of his
theory that mineral samples he had collected in the Pampas had formed in an estuary
and so should contain marine foraminifera (Darwin Correspondence Project Letter
no. 870 2020a).
Darwin reported that Ehrenberg’s examination of the dust that he had collected and
dust that had been collected later by Lieutenant Robert Bastard James of the HMS
Spey off the northwest coast of Africa were both composed in large part of infusoria,
including over 67 different forms (Darwin 1846). His dust and that of Lieut. James
contained 37 species in common. All but two species were freshwater organisms.
Oddly, none of these had been found to be of Saharan African origin based on
Ehrenberg’s previous studies. Instead, they were South American or Senegalese
species. This was contrary to where it appeared the dust came from, based on the
wind direction at the time of its deposition. Darwin commented, “I think there can be
no doubt that the dust which falls in the Atlantic does come from Africa. How to
explain the enigma of the absence of characteristic African forms and of the presence
of two species from S. America, I will not pretend to conjecture” (Darwin 1846).
A dispute over the origin of the Pampas region of South America was a subject
that Darwin hoped Ehrenberg’s examinations could help settle. The French geologist
Alcide de
0 Orbigny posited that this raised geological formation had been formed
through a catastrophic inundation of seawater. Darwin contended that it had formed
through a gradual process involving formation of an estuary of freshwater or
brackish water and mud (Jardine 2009). Darwin sent Ehrenberg soil samples collected there, and he reported, “. . .Professor Ehrenberg has had the kindness to
examine for me a little of the red earth, taken from low down in the deposit, . . .
and he finds in it many infusoria, partly salt-water and partly fresh-water forms, with
the latter rather preponderating; and therefore, as he remarks, the water must have
been brackish. . . . this shows that just before the Pampas was slowly elevated into
dry land, the water covering it was brackish” (Darwin 1845).
2.5 Natural Taxonomy: Phylogeny-Based Systematics
After his death, Darwin’s greatest impact on the development of microbiology was
the effect of his theory of evolution on the systematics of microorganisms. Taxonomy of plants and animals before Darwin’s theory was largely based on the scheme
of Carl Linnaeus, though other taxonomic schemes were attempted. In his work on
2 Darwin’s Science’s Impact on the Evolution of the Microbiological Sciences
25
Chinese frontier in 1829, Ehrenberg began a 30-year study of infusoria in soils,
sediments, rocks, and dust samples that he and others had collected from around the
world. He studied and named many species of protists and diatoms, in particular. He
attempted to associate different species with their geographic distribution. It was
these studies that attracted Darwin’s attention. Darwin thought that his samples
would help him extend his biogeographic studies to the microbial world. He also
thought that the microbiology of some of his rock samples would help him prove
how those sedimentary rocks formed. In particular, he was looking for proof of his
theory that mineral samples he had collected in the Pampas had formed in an estuary
and so should contain marine foraminifera (Darwin Correspondence Project Letter
no. 870 2020a).
Darwin reported that Ehrenberg’s examination of the dust that he had collected and
dust that had been collected later by Lieutenant Robert Bastard James of the HMS
Spey off the northwest coast of Africa were both composed in large part of infusoria,
including over 67 different forms (Darwin 1846). His dust and that of Lieut. James
contained 37 species in common. All but two species were freshwater organisms.
Oddly, none of these had been found to be of Saharan African origin based on
Ehrenberg’s previous studies. Instead, they were South American or Senegalese
species. This was contrary to where it appeared the dust came from, based on the
wind direction at the time of its deposition. Darwin commented, “I think there can be
no doubt that the dust which falls in the Atlantic does come from Africa. How to
explain the enigma of the absence of characteristic African forms and of the presence
of two species from S. America, I will not pretend to conjecture” (Darwin 1846).
A dispute over the origin of the Pampas region of South America was a subject
that Darwin hoped Ehrenberg’s examinations could help settle. The French geologist
Alcide de
0 Orbigny posited that this raised geological formation had been formed
through a catastrophic inundation of seawater. Darwin contended that it had formed
through a gradual process involving formation of an estuary of freshwater or
brackish water and mud (Jardine 2009). Darwin sent Ehrenberg soil samples collected there, and he reported, “. . .Professor Ehrenberg has had the kindness to
examine for me a little of the red earth, taken from low down in the deposit, . . .
and he finds in it many infusoria, partly salt-water and partly fresh-water forms, with
the latter rather preponderating; and therefore, as he remarks, the water must have
been brackish. . . . this shows that just before the Pampas was slowly elevated into
dry land, the water covering it was brackish” (Darwin 1845).
2.5 Natural Taxonomy: Phylogeny-Based Systematics
After his death, Darwin’s greatest impact on the development of microbiology was
the effect of his theory of evolution on the systematics of microorganisms. Taxonomy of plants and animals before Darwin’s theory was largely based on the scheme
of Carl Linnaeus, though other taxonomic schemes were attempted. In his work on
2 Darwin’s Science’s Impact on the Evolution of the Microbiological Sciences
25