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Darwin Correspondence Project


Sources|Discussion Questions|Experiment

Darwin and barnacles

Darwin’s interest in Cirripedia, a class of marine arthropods, was first piqued by the discovery of an odd burrowing barnacle, which he later named “Mr. Arthrobalanus," while he was aboard the HMS Beagle. After completing four Beagle-related publications, Darwin dissected, classified, and wrote about barnacles on a daily basis from 1846 to 1854. Ultimately, Darwin's deep and focused research on barnacles resulted in the publication of four serious monographs, which established him as a major figure in the British zoological community. (Darwin's earlier geological publications had already established him as a man of scientific merit).

Barnacles and speciation

Darwin’s work on barnacles was a key component in the theory of speciation he published in his 1859 magnum opus On the Origin of Species. By studying a group of organisms in its entirety, both living forms and fossilized remains, Darwin was able to see the fascinating variety among related individual forms and to understand how this diversity might have developed over time. In his studies, Darwin classified the various barnacle groups using an innovative theoretical framework. For instance, though he used the term 'homology' in some of his work in the standard 19th-century fashion (i.e., the same organ in different animals with a variety of forms and functions), he also used it in a more evolutionary sense by comparing barnacle larvae to adults and by comparing barnacles to crustaceans more generally. Significantly, Darwin's detailed research into a single class--in this case Cirripedia--provided substantive evidence of the broad and sweeping theory of evolution by natural selection he proposed in On the Origin of Species. This body of evidence helped Darwin convince his readers of the validity of his ideas.

You can download the entire packet of reading materials here: Barnacle Source Packet



Grant, R.E. 1827. Notice regarding the Ova of the Pontobdella muricata, Lam. The Edinburgh Journal of Science Vol. VII. April-October: 160-161, index and Plate II.

Grant, R.E. 1827. Observations on the Structure and Nature of Flustra.The Edinburgh New Philosophical Journal April-October: 337-342.

Barrett, P. H. ed. 1977. “On the Ova of Flustra, or, Early Notebook, Containing Observations Made by C.D. When He Was at Edinburgh, March 1827.” In Barrett, P. ed., The collected papers of Charles Darwin. 2 vols. Chicago: University Press, 2: 285-91.


Browne, Janet. 2008. Darwin's Origin of Species: A Biography. New York: Grove Press. (p.1 - 83)


Letter Packet: Darwin's Barnacles

Letter 1015—Darwin to J. D. Hooker, [18 Oct 1846]

In a quick note to his friend and colleague, Joseph Dalton Hooker, Darwin proposes a social visit in conjunction with his trip to London to have Mr. Arthrobalanus illustrated.

Letter 1022—Darwin to J. D. Hooker, [12 Nov 1846]

One month later, he writes to Hooker again discussing the unusual anatomy of Mr. Arthrobalanus.

Letter 1140—Darwin to J. C. Ross, 31 Dec 1847

Darwin writes to James Clark Ross, officer in the British navy and polar explorer, asking him to collect and preserve specimens of Cirripidea on his upcoming expedition to the Arctic in search of the lost explorer John Franklin.

Letter 1253—Darwin to Albany Hancock, [21 Sept 1849]

Darwin writes to barnacle expert Albany Hancock to ask him to share preserved specimens with him.

Letter 1370—Darwin to Syms Covington, 23 Nov 1850

In this letter, Darwin thanks his former servant, Syms Covington, for sending him a box of barnacles from Australia.

Supplementary Reading

Stott, Rebecca. 2004. Darwin and the Barnacle. New York: Farber & Farber.


1. Why is Darwin interested in the barnacle he eventually names "Mr. Arthrobalanus"? Why do you think this barnacle inspired Darwin to study barnacles for eight years?

2. How does Darwin use correspondence to contribute to his study of Cirripidea? How crucial do you think the specimens and information he obtained through correspondence were to his studies?

3. From what regions does Darwin request barnacle specimens? Why was it necessary for him to have specimens from so many different parts of the world?

4. How did Darwin's observations of the immense variation in Cirripidea influence his views on the mutability of species? Describe the significance of Darwin's barnacle work to his ideas in On the Origin of Species.


Here is an example of a classroom activity performed at Harvard:

After reading about and discussing Darwin’s observations of barnacles, the class went to the Harvard Museum of Comparative Zoology. There the class viewed the museum’s collection of prepared barnacle slides, many of them from the period in which Darwin’s own barnacle collection was being put together. After visiting the museum, the class collected its own fresh barnacle specimens from nearby Woods Hole in Massachusetts. The students were then able to observe both the prepared barnacle slides and the fresh barnacles specimens under microscopes. Observing barnacles first-hand enabled the students to better understand Darwin’s appreciation for these creatures.

Although your university may not have its own barnacle specimen collections, many public natural history museums have similar collections. If you are located near a coast, barnacles are easily obtained from ship pilings or intertidal rock groupings. Your students could explore Darwin’s notes on his observations of flustra, and then make their own observations.

Learning objectives

In this teaching module, you will find the resources necessary to discuss Darwin’s observations and experiments with barnacles, and relate them to his thoughts on speciation. This module also provides an opportunity to examine how Darwin used correspondence to collect specimens and evidence for his scientific work. 

1. discuss Darwin’s fascination with barnacles 

2. examine the contribution of Darwin’s work with barnacles to his theory of speciation

3. explore the relationship between empirical observation and scientific theory