conscious decisions.It has nothing to do with the meaning of words,
phrases,or sentences being uttered.
Drift in whale song proceeds at a much faster rate than linguistic drift.
Most changes originate as modifications of preexisting material,but
within one decade a population’s song may undergo so much change that
one can no longer recognize its relation to the earlier version.
How do whales remember the current version of their song in the
context of such a rapidly changing oral culture? Do they process mate-
rial in memorable groups of units or chunks,as humans apparently do?
(Miller 1956;Simon 1974).Linda Guinee and I noticed,while compar-
ing whale songs from many years in two geographically isolated popu-
lations,that when songs were most complex they tended to contain
several adjacent themes whose phrases had similar beginnings or endings
(figure 9.9).Reminded of the fact that human rhyming sometimes acts
as a mnemonic device,we speculated that rhymelike phrases might help
whales remember the sequence of material in their rapidly changing
song.To test this notion we collated the occurrence of rhymes in 548
songs (from seven years in the eastern North Pacific and twelve years in
the western North Atlantic) with the number of themes these songs con-
tained,a rough measure of complexity.We found a strong correlation,
with the most complex songs containing the most rhyming (figure 9.10).
In the same sample we found no relationship between rhyming and song
duration,which may reflect repetition and not complexity.This pair of
measurements strengthened our hunch that rhyming might play a role
in whales’ ability to keep up with current versions of their songs.
In the interest of clarity I have selected quite simple examples to illus-
trate the process of whale song evolution;songs of many periods showed
greater variation in phrase and theme structure.In fact the further one
looks,the more variation one finds.Eventually one discovers that the
variation extends to the structure as well as the contents of the phrases
and themes (Payne,Guinee,and Heyman-Levine,unpublished data).
Like the songs themselves, the story of their evolution is ever
developing.
Further studies of humpback whales’ improvisational tendencies will
be interesting as we continue to compare the vocal behavior of other
animals with our own musical behavior.Most changes in human music
reflect a blending of external and internal influences,making it difficult
to isolate those that might be intrinsic to the process of singing itself.
Song changing in whales appears to be less affected by outside influences,
and to offer a cleaner window on the mental processes of these
composers.
I can imagine many questions that human composers would like to ask
whales.It would be nice to know,for instance,whether whales are aware147 The Changing Songs of Humpback Whales