70 Science & technology The EconomistDecember 14th 2019
This photograph shows the world’s oldest known art gallery. It is
in a cave in Sulawesi, an island in Indonesia. It was discovered by
a team led by Adam Brumm of Griffith University, in Australia,
and is reported in this week’s Nature. The most ancient pictures
in it date from 43,900 years ago—27,000 years before the
well-known cave paintings at Lascaux, in France. Among the
exhibits are two pigs and four dwarf buffalo. There are also eight
figures that appear, on first glance, to be human, but which closerPictures at an exhibition
examination suggests also have animal features. One seems to
have a tail, another a beak. Others have muzzles or snouts. Such
constructs are known as therianthropes, and are found in many
cultures (the centaurs of ancient Greece, for example, or the
jackal-headed Egyptian god Anubis). The oldest known European
therianthrope is a statue of a lion-headed man which dates from
about 40,000 years ago. That ancient Sulawesians had similar
ideas suggests therianthropy has deep roots in human culture.W
hy arewhales so big? One answer is
simply that they can be. The size of
land animals is constrained in part by their
need to support themselves against the
force of gravity. Marine creatures have that
support provided free, by the medium they
live in. Even so, what is possible is not al-
ways sensible. Resources put into growth
are unavailable for reproduction. Given
that whales can and do become big, how-
ever, a second question arises: what, if any-
thing, stops them being even bigger? Je-
remy Goldbogen of Stanford Universityand his colleagues suspect that the an-
swers to both questions are related to the
animals’ food supply. And, as they describe
in a paper in Science, they have gathered
data that illuminate how this might work.
Broadly, big whales come in two variet-
ies. Toothed whales, such as sperm whales
(pictured above), hunt individual prey. Ba-
leen whales suck in mouthfuls of water and
extract small organisms such as krill, using
fibrous buccal filters. The biggest whales of
all (blue, humpback and so on) are baleen
whales. This might be viewed as paradoxi-cal, because on land, as predators get big-
ger, so do their individual prey.
Both toothed and baleen whales often
hunt by diving deep—prey being more
abundant at depth. To do this they have to
hold their breath, which limits how long
they can stay underwater. One explanation
of giantism in whales is that because bigger
whales can hold their breath longer, they
can spend more time hunting. But that will
only hold good as long as the extra time is
spent productively.
Dr Goldbogen and his team attached
water-and-pressure-proof data-recording
tags to a range of both toothed and baleen
cetaceans, to see what they got up to on
their hunting dives. In particular, acceler-
ometers in the tags could record the sud-
den changes of speed, such as lunging
movements, that are associated with pred-
atory behaviours.
Counting whale hunts per dive in this
way, and knowing from previous studies
what types of prey particular cetaceans fa-
vour, the researchers were able to work out
the feeding efficiencies—energy in versus
energy out—of the two sorts of whale.
Toothed whales, they found, are living on
the edge, size-wise. The number of individ-
ual prey they are able to chase and capture
in a single dive is just enough to sustain an-
imals of their size. By contrast, the baleen
whales the researchers looked at, once they
have encountered a shoal of prey, are in nu-
tritional nirvana. A single lunge by a large
rorqual, they reckon, can capture ten times
as much food as the largest individual prey
taken by toothed whales.
Toothed whales thus do seem to have
hit some sort of size limit. Perhaps, though,
baleen whales might continue to evolve
and get bigger still. The blue whale is, at the
moment, the largest animal, extant or ex-
tinct, know to have lived. Might its descen-
dants be larger yet? 7How cetaceans got so large is a trade off between dive time and hunting successEvolutionA whale of a tale