ittered with tiny white holes. These are called wormholes, and inaccurately so—they’re actually the work of beetles. The adults laid their eggs in crevices within the trunks of trees. The grubs slowly bored their way through the wood, eventually transformed into adults, and burrowed their way out of their shelters. The artists who transformed the tree trunks into printing blocks also inherited the exit-holes of the adult beetles, which left small circles of empty whiteness when pressed onto pages.
The beetles only emerged a year or so after the blocks were carved. The holes they left must have been frustrating, but remaking them would have been expensive. So the blocks were kept and reused despite their defects, unless the beetles had really gone to town. The holes they left behind preserve a record of wood-boring beetles, across four centuries of European literature. These holes are trace fossils. They’re evidence of beetle behaviour that’s been printed into old pages, just as dinosaur tracks were printed into the earth.
Now, Blair Hedges from Pennsylvania State University has used these fossils to study the history of the beetles that made them.
Every time you put on some music or listen to a speaker’s words, you are party to a miracle of biology – the ability to hear. Sounds are just waves of pressure, cascading through sparse molecules of air. Your ears can not only detect these oscillations, but decode them to reveal a Bach sonata, a laughing friend, or a honking car.
This happens in three steps. First: capture. The sound waves pass through the bits of your ear you can actually see, and vibrate a membrane, stretched taut across your ear canal. This is the tympanum, or more evocatively, the eardrum. On the other side, the eardrum connects to three tiny well-named bones—the hammer, anvil and stirrup—which link the air-filled outer ear with the fluid-filled inner ear.
The bones perform the second-step: convert and amplify. They transmit all the pressure from the relatively wide eardrum into the much tinier tip of the stirrup, transforming large but faint air-borne vibrations into small but strong fluid-borne ones.
These vibrations enter the inner ear, which looks like a French whisk poking out of a snail shell. Ignore the whisk for now – the shell is the cochlea, a rolled-up tube that’s filled with fluid and lined with sensitive hair cells. These perform the third step: frequency analysis. Each cell responds to different frequencies, and are neatly aligned so that the low-frequency ones are at one end of the tube and the high-frequency ones at another. They’re like a reverse piano keyboard that senses rather than plays. The signals from these cells are passed to the auditory nerve and decoded in the brain. And voila – we hear something.
All mammal ears work in the same way: capture sound; convert and amplify; and analyse frequencies. But good adaptation are rarely wasted on just one part of the tree of life. Different branches often evolve similar solutions to life’s problems. And that’s why, in the rainforests of South America, a katydid—a relative of crickets—hears using the same three-step method that we use, but with ears that are found on its knees.
For corals, gardening’s a matter of life and death. Corals compete with algal seaweeds for space, and many types of seaweed release chemicals that are toxic to corals, act as carriers for coral diseases and boost the growth of dangerous microbes. These dangers require close contact—the seaweed poisons won’t diffuse through the water, so they need to be applied to the corals directly. And that gives the corals an opportunity to save themselves. When they sense encroaching seaweed, they call for help.
Danielle Dixson and Mark Hay from the Georgia Institute of Technology have found that when Acropora corals detect the chemical signatures of seaweed, they release an odour that summons two gardeners – the broad-barred goby and redhead goby. These small fish save the corals by eating the toxic competitors. In return, one of them stores the seaweed poisons in its own flesh, b