Project Amaze!

In chapter 10, Ryland first realizes that Rocky can hear. He describes the sounds that Rocky produces as “whale song” but then corrects that to “whale chords”, as several notes are produced at once. Ryland reflects on how amazing it is that each of them can hear the sounds that the other produces: “He’s from a different planet, and totally different evolutionary line, but we ended up with compatible sound ranges.” 10.091

After Rocky boards the Hail Mary, we (and Ryland) learn that Eridians can hear much better than humans: “Rocky is two floors below me, but I speak at a normal volume. I know he can hear it just fine.” 17.019 After establishing Rocky’s hearing prowess, we eventually also discover that he can hear at much higher and lower frequencies than Ryland can (though, of course, there is overlap which allows them to more easily communicate).

This leads to a fascinating discussion between the two spacefarers about how such an overlap in hearing range arose, with Rocky hypothesizing that “Sound of object touching object very important”. 21.114 In other words, it is evolutionarily advantageous to select for the ability to hear objects colliding.

While we cannot yet compare hearing ranges between Earth life and extraterrestrials, we need not escape our own planet to find organisms who hear differently than humans.

Elephants are known to use infrasound, sound in frequencies below the range of human hearing (with a typical human range being around 20 to 20,000 Hz). This is especially advantageous for elephants who reside in forests, as low frequency sounds can travel greater distances through closed habitats than higher frequency sounds. These low frequency elephant “rumbles” seem to communicate anything from “let’s go” to “help, I’m lost”.

Bottlenose dolphins can hear in ultrasonic tones, detecting frequencies of around 75 Hz to over 150,000 Hz. Of course, dolphins also utilize echolocation, which we discussed briefly in #116. If we want to find the ultrasonic hearing champion, however, we will need to turn our gaze away from charismatic megafauna.

The greater wax moth, with its tiny micro-acoustic ear, has evolved to hear frequencies up to 300,000 Hz. At least one study has investigated whether this developed as part of an evolutionary arms-race against bats, who also utilize high frequencies.

“That is sound of predator approaching you. That is sound of prey running away” 21.114 seems to have been a valid consideration regarding the evolution of hearing. Well done, Rocky.