Graphics Reference
In-Depth Information
FIG 4.2
Different beak shapes are
suited to different tasks and diets.
such as meat, water insects, seeds, or nectar. The differences may be much
more subtle than that, but they are no less marked. Certain hummingbirds
have beaks of a particular length to reach and exploit the nectar that can be
found deep inside the flowers of specific plants. One species of hummingbird
has evolved a beak so long it is no longer able to reach its own preen glands
with its beak, as most birds do, and has had to develop an alternative way of
reaching backward with its feet to get at the valuable oil from the preen gland
to keep its feathers in tip-top condition.
Evolutionary development is not limited to the size and shape of an animal
but also extends to the animal's movement, though size and shape certainly
affect and enable specific types of movement. The evolution of the cheetah,
for example, has resulted in a physiognomy that provides both strength and
agility, enabling the cat to achieve the fantastic speed and extreme level of
maneuverability needed to catch the very agile prey on which it feeds.
Evolutionary forces apply to every detail of animal physiognomy. Teeth
needed to tear flesh have become strong, long, and sharp. Ears needed
