Earthworms
Sources|Discussion Questions|Experiment
Earthworms and Wedgwood cousins
As with many of Darwin’s research topics, his interest in worms spanned nearly his entire working life. Some of his earliest correspondence about earthworms was written and received in the 1830s, shortly after his return from his Beagle voyage, and his last letters about worms were written only months before he died in March 1882. In the same way that Darwin cast a wide net when seeking information on pigeon morphology, the action of climbing plants, and biogeography, Darwin wrote to friends and contacts near and far to collect information on worms. Some of his most faithful informants and observers of the actions of earthworms were members of his own family, in particular his nieces, Lucy and Sophy Wedgwood, the daughters of Emma Darwin’s brother Josiah. Darwin relied on and valued the careful observations of these two young women, even going so far as to submit Lucy Wedgwood’s observations for publication in the Gardeners’ Chronicle.
After Figure 1, The formation of vegetable mould, By Charles Darwin, Credit: Biodiversity Heritage Library/University of Toronto, http://www.biodiversitylibrary.org/bibliography/21214
Scientific evidence for the history of life
Darwin chose to study earthworms in order to fill out the details of his theory of evolution by natural selection. His book Fertilisation of Orchids (1862) was Darwin’s “flank movement against the enemy”; it argued that the intricacies of adaptation could have arisen from natural selection working alone. Similarly, The Power of Movements in Plants (1880) was a study of incredible empirical detail that demonstrates Darwin’s creative experimental methods. Darwin’s study of earthworms was a treatise on the power of present day observations for making inferences about past events. The philosophy of a historical science (be it geology or evolutionary theory) was a subject that Darwin had contemplated from his earliest days as a naturalist. As his final published work, The Formation of Vegetable Mould through the Action of Worms was a fitting end to a lifetime of varied natural studies and theoretical work.
You can download the entire packet of reading materials here: Earthworms Source Pack
SOURCES
Papers
Darwin, C.R. 1840. On the formation of mould. Transactions of the Geological Society (Ser. 2) 5:505-509.
Darwin, C.R. 1881. The Formation of Vegetable Mould, Through the Action of Worms. London: John Murray. Chapters 1 and 3.
This exchange of letters between Darwin and his niece Lucy, aged 26 at the time, demonstrates Darwin’s solicitation of information, his niece’s readiness to comply with his request, and his gratitude for her observations.In his last letter touching on earthworms, written less than three months before his death, Darwin remarks on the degree to which evolutionary theory has penetrated young scientists working “in any branch of Biology.” Darwin likens the views of a disbeliever who reviewed Earthworms to those of the thinkers who stood against heliocentrism.
Gould, S.J. “A Worm for a Century and all Seasons” reprinted in Hen’s Teeth and Horses Toes.
In an essay for Natural History magazine, Stephen Jay Gould argues for the importance of Darwin’s last book and its centrality to Darwin’s view of history.
DISCUSSION QUESTIONS
1. What do you think of Darwin’s letter to John Murray? What does Darwin make of the influence of his own theory on the discipline of biology?
2. How does Darwin request the help of his nieces? What does the tone of Darwin’s correspondence with his nieces tell you about Darwin’s domestic life and extended family?
3. How does Darwin praise the observational abilities of his son and nieces? What do you make of his relationship to them through the correspondence?
4. What do you think of Darwin’s final book? Would you have expected this to be the final topic Darwin touched on in his scientific career? How does this topic relate to the rest of Darwin’s scientific work?
EXPERIMENT
Observe earthworms as Darwin did! You will need:
- several small plastic pots
- moist potting soil
- earthworms (which can be ordered)
- a string instrument (piano, upright base, violin etc.) and someone to play it
Method:
Put the earthworms into the clay pots, about 20-30 in each pot. Observe them first without playing any music. How are they moving? Do they react to movements of the pots? Do you have a baseline for their behavior to start the experiment?
Play music for the earthworms. Do they react? Why do you think Darwin wanted to carry out this experiment? Can you relate your own observations to the letter selections for this module?
Do the earthworms react to vibrations that touch the soil? What about vibrations in the air? What does this tell you about the way that earthworms ‘hear’?
Objectives:
- make detailed observations of earthworms’ movements and habits
- observe whether earthworms react to music
- discuss why Darwin did this experiment
- relate your experience to Darwin’s discussion of earthworms in the correspondence
To see an example of this activity, as performed at Harvard University, click here!