Charles Darwin Yelled at Worms!
By Gregory Vogel
Darwin not only yelled at worms, he appears to have serenaded them with musical instruments as well.
The idea of evolution through natural selection was of course Darwin's greatest contribution to the natural sciences (and understanding evolutionary concepts is essential to understanding the natural world), but he wrote about a great many other topics as well. He wrote an entire book about earthworms and how they alter the soil, titled:
ACTION OF WORMS,
OBSERVATIONS ON THEIR HABITS.
CHARLES DARWIN, LL.D., F.R.S.
(It's too bad we aren't writing books with titles like that anymore.)
In this book, Darwin is mostly interested in how earthworms influence soil formation, but he explores general earthworm physiology as well. There were lots of popular ideas about earthworms at the time, but little had been written about them formally. Being a trained natural scientist, Darwin conducted numerous experiments, and systematically observed the behavior of earthworms under many different conditions. Do they see or can they sense light at all? Do they feel hot or cold? Can they smell? Are they sensitive to vibrations? Can they hear?
Darwin's explanations of how he went about testing these questions are very fun to read, and quite instructive as narratives of basic scientific inquiry. When testing whether worms could hear or not, for example, he tried many different sounds, both high- and low-pitched. He played a tin whistle, a bassoon, and the piano for them to see if they would react. (Maybe he had a musician help him, but I like to imagine it was Darwin playing the instruments.) When he played the piano for them, he was careful to make sure that the vibrations from the instrument did not reach them, because this is a separate variable. When he shouted at them (I wonder what he shouted?), he was careful to make sure that his breath didn't strike them.
These experiments, it seems to me, would be wonderful classroom exercises to teach biology and to introduce basic concepts of scientific inquiry. All of the observations and experiments Darwin explains in this book are 'tabletop' science - no special equipment is necessary, and they are simple enough that they require no special training. They are compelling arguments because they are understandable and they are testable.
Below is a short excerpt from Darwin's book on worms (pages 26-28).
Worms do not possess any sense of hearing. They took not the least notice of the shrill notes from a metal whistle, which was repeatedly sounded near them; nor did they of the deepest and loudest tones of a bassoon. They were indifferent to shouts, if care was taken that the breath did not strike them. When placed on a table close to the keys of a piano, which was played as loudly as possible, they remained perfectly quiet.
Although they are indifferent to undulations in the air audible to us, they are extremely sensitive to vibrations in any solid object. When the pots containing two worms which had remained quite indifferent to the sound of the piano, were placed on the instrument, and the note C in the bass clef was struck, both instantly retreated into their burrows. After a time they emerged, and when G above the line in the treble clef was struck they again retreated. Under similar circumstances on another night one worm dashed into its burrow on a very high note being struck only once, and the other worm when C in the treble clef was struck. On these occasions the worms were not touching the sides of the pots, which stood in saucers; so that the vibrations, before reaching their bodies, had to pass from the sounding board of the piano, through the saucer, the bottom of the pot and the damp, not very compact earth on which they lay with their tails in their burrows. They often showed their sensitiveness when the pot in which they lived, or the table on which the pot stood, was accidentally and lightly struck; but they appeared less sensitive to such jars than to the vibrations of the piano; and their sensitiveness to jars varied much at different times. It has often been said that if the ground is beaten or otherwise made to tremble, worms believe that they are pursued by a mole and leave their burrow. I beat the ground in many places where worms abounded, but none emerged. When, however, the ground is dug with a fork and is violently disturbed beneath a worm, it will often crawl quickly out of its borrow.