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To Thomas Davidson   23 December [1856]

Summary

Asks TWStCD about variation among brachiopods.

Author:  Charles Robert Darwin
Addressee:  Thomas Davidson
Date:  23 Dec [1856]
Classmark:  American Philosophical Society (Mss.B.D25.142)
Letter no:  DCP-LETT-2021

From Thomas Davidson   29 December 1856

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.]

Author:  Thomas Davidson
Addressee:  Charles Robert Darwin
Date:  29 Dec 1856
Classmark:  DAR 162: 116
Letter no:  DCP-LETT-2024

To Thomas Davidson   26 April 1861

Summary

Asks TWD to carry out research on brachiopods to see whether the forms in one formation are intermediate between those above and below.

Describes unpublished study of spirifers by J. W. Salter.

Author:  Charles Robert Darwin
Addressee:  Thomas Davidson
Date:  26 Apr 1861
Classmark:  DAR 143
Letter no:  DCP-LETT-3128

To Thomas Davidson   30 April 1861

Summary

Thanks TWD for his letter. Difficulties with CD’s theory are many and great, but CD thinks the reason is that we underestimate our ignorance. The imperfection of the geological record counts heavily for CD. His greatest trouble is weighing "the direct effects … of changed conditions of life without any selection, with the action of selection on mere accidental (so to speak) variability. I oscillate much on this head, but generally return to my belief that the direct [effects] … have not been great."

Is surprised that any one, like W. B. Carpenter, can go as far as to believe all birds may have descended from one parent, but will not go further and include all the members of the same great division. Such beliefs make "Divine mockeries" of morphology and embryology, the most important of all subjects.

Author:  Charles Robert Darwin
Addressee:  Thomas Davidson
Date:  30 Apr 1861
Classmark:  DAR 143
Letter no:  DCP-LETT-3131

From Thomas Davidson   3 May 1861

Summary

Sends three tables on the known geological distribution of genera and subgenera of Brachiopoda. Has been continually puzzled by intermediate forms, and is convinced that the greater number of species can be linked together. "Natura non facit saltum."

Author:  Thomas Davidson
Addressee:  Charles Robert Darwin
Date:  3 May 1861
Classmark:  DAR 99: 1–2
Letter no:  DCP-LETT-3135

To Thomas Davidson   7 April 1873

Summary

Thanks TWStCD for catalogue of his Cretacean fossils.

Regrets he cannot visit Brighton.

Author:  Charles Robert Darwin
Addressee:  Thomas Davidson
Date:  7 Apr 1873
Classmark:  American Philosophical Society (Mss.B.D25.426)
Letter no:  DCP-LETT-8845
Document type
letter (6)
Correspondent
Date
1856 (2)
1861 (3)
1873 (1)
letter