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ehavior, evolution of
In another species of digger wasp, the female visits her
various burrows each day. The burrows contain larvae of
different ages, therefore of different sizes. The female provides
various sizes and numbers of paralyzed insects to
them, depending on the amount of food that they need. This
appears at first to be reasoning, but it actually is not. When
a scientist experimentally exchanged the larva in one burrow
for the larva in another, the female did not notice, but continued
for a while to provide food to the burrow proportional to
the size of its original, not its current, inhabitant. The female
wasp is not reasoning but is following a fixed action pattern.
Eventually the pattern is reset as the wasp gathers updated
information about the sizes of the larvae.
Another example is the honeybee. A colony of honeybees
(Apis mellifera) can contain up to 80,000 bees, all sisters or
half sisters, the offspring of a single queen. Many of the bees
collect food within a radius of several kilometers.
Near the entrance, worker bees stand and buzz their
wings, creating an air current that cools the nest. Other
worker bees, the foragers, bring home loads of nectar and
pollen that they have gathered from flowers. The foragers do
not visit flowers indiscriminately, but only those flowers that
are structurally suited to bee pollination. A bee drinks nectar
with its proboscis and stores it in a special sac; a valve
prevents the nectar from entering the stomach. While still
visiting the flowers, the foragers rake the pollen off of their
bristles and cram it into pollen baskets on the hind legs.
The foragers crawl into the darkness of the nest. The
nest contains thousands of perfectly hexagonal chambers,
which not only serve as honeycombs but also as brood chambers.
The chambers are composed of beeswax secreted by
workers’ wax glands. When the nectar-laden forager finds an
empty chamber, she regurgitates the nectar from the nectar
sac. She turns perishable nectar into well-preserved honey by
regurgitating an enzyme that breaks the sucrose into simpler
sugars and an acid which helps prevent bacterial contamination.
Numerous other workers inside the nest fan their wings,
helping to evaporate water out of the honey.
A forager called a scout arrives, having located a new
patch of flowers. She places herself in the midst of a crowd of
her sisters and begins to dance. If the nectar source is nearby,
she performs a round dance which merely excites the other
foragers to rush out and search in the vicinity of the hive. If
the patch of flowers is distant, she performs a complex waggle
dance. The timing and direction of her movements communicate
information about the distance and the direction of
the patch of flowers. In the darkness of the hive, this information
is communicated by touch and sound. A faster dance
communicates that the patch of flowers is farther away. The
scout performs the dance in a figure eight, with a straight run
in the middle during which the scout waggles her abdomen
back and forth rapidly. The direction of the straight run communicates
the direction of the food. It does not point directly
to the food, because the honeycomb surface on which the
scout performs the dance is vertical. The other foragers must
interpret the direction of the food as a human would interpret
a line drawn on a map on the wall. If the scout had flown a
detour in order to find the food, her dance would have communicated
not the distance and direction of the detour but
the direction of a straight flight to the food!
The other foragers use the direction of the Sun to interpret
the waggle dance information. What do they do if the Sun
is hidden behind clouds? Bees are able to see the direction of
the polarization of light, therefore they can determine where
the Sun is located behind the clouds. If the straight run of the
scout’s waggle dance is vertical, this communicates to the other
foragers that the food is in the same direction as the Sun. A
straight downward run indicates that the food is in the opposite
direction. Intermediate directions of the straight run indicate
the approximate direction to the left or right of the Sun.
The Earth turns and the Sun appears to move across the
sky. The bees compensate for this movement with their internal
biological clocks which provide them with a mental map
of the Sun’s location in the sky at various times of day. If a
scout is caught and imprisoned for several hours in a dark
box, then released directly into the dark hive, she communicates
the direction of the nectar source relative to where the
Sun currently is located, not where the Sun was located when
she was captured. She rotates the direction of the straight run
of the dance as if it were the hour hand of a 24-hour clock.
Bees raised in the Southern Hemisphere also rotate their
dance direction, but in reverse. Other workers then leave for
the new nectar source, flying in the right direction and carrying
only enough food to supply them for the distance that the
scout communicated to them.
Although these actions are complex, they are instinctive
fixed action patterns. Each bee has relatively little intelligence,
but their interactions can result in a hive that displays
a collective intelligence that far surpasses that of any constituent
individual (see emergence).
Another example is the blue-footed booby. The bluefooted
booby of the Galápagos Islands defines its nesting
territory by dropping a ring of guano, as shown in the
figure on page 43. It treats any nestling booby that is within
the circle as its own offspring and totally ignores any nestling
that is outside the circle, even when its cries of starvation can
be plainly heard. The parents’ caretaking behavior is a fixed
action pattern.
Humans also have fixed action patterns. Many facial
expressions are instinctive and are more complex than typical
muscular reflexes. People who have been blind from birth,
and who have never seen anyone smile, still smile.
3. Learning. A bird sings because it learns how to sing.
Fixed action patterns can be modified by learning. In all three
of the above examples, the actual form of the fixed action
pattern is modified by learning. A bird learns many of its
songs by watching and listening to other birds, and to birds
of other species. Mockingbirds are famous for their diverse
patterns of singing. Due to learning, no two mockingbirds
have exactly the same repertoire of songs. Some birds, such
as parrots, have a very highly developed ability to learn
new vocalizations. The domestication and training of many
mammals has demonstrated that they are capable of learning
a greater variety of behavior than they typically display