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Darwin, C. R. in correspondent 
Davidson, Thomas in correspondent 
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From:
Charles Robert Darwin
To:
Thomas Davidson
Date:
23 Dec [1856]
Source of text:
American Philosophical Society (Mss.B.D25.142)
Summary:

Asks TD about variation among brachiopods.

Contributor:
Darwin Correspondence Project
From:
Thomas Davidson
To:
Charles Robert Darwin
Date:
29 Dec 1856
Source of text:
DAR 162: 116
Summary:

His experience confirms CD’s view that some species and even some genera of Brachiopoda are consistently more variable than others, and that such variable forms are variable in all localities and at all periods. Similarly a species that shows a lack of variability does so at all points in time and space. Discusses the causes of variability. [See Natural selection, p. 106.]

Contributor:
Darwin Correspondence Project