Evolution__3rd_Edition

6 PART 1 / Introduction
Examples exist of adaptation
Adaptation has to be explained, ...
. . . and is, by natural selection
find in the living world. Adaptation refers to “design” in life a to those properties of
living things that enable them to survive and reproduce in nature. The concept is easiest
to understand by example. Many of the attributes of a living organism could be used to
illustrate the concept of adaptation, because many details of the structure, metabolism,
and behavior of an organism are well designed for life.
The woodpecker provided Darwin’s favorite examples of adaptation. The woodpecker’s
most obvious adaptation is its powerful, characteristically shaped beak. It
enables the woodpecker to excavate holes in trees. They can thus feed on the yearround
food supply of insects that live under bark, insects that bore into the wood, and
the sap of the tree itself. Tree holes also make safe sites to build a nest. Woodpeckers
have many other design features as well as their beaks. Within the beak is a long, probing
tongue, which is well adapted to extract insects from inside a tree hole. They have a
stiff tail that is used as a brace, short legs, and their feet have long curved toes for gripping
on to the bark; they even have a special type of molting in which the strong central
pair of feathers (that are crucial in bracing) are saved and molted last. The beak and
body design of the woodpecker is adaptive. The woodpecker is more likely to survive, in
its natural habitat, by possessing them.
Camouflage is another, particularly clear, example of adaptation. Camouflaged species
have color patterns and details of shape and behavior that make them less visible
in their natural environment. Camouflage assists the organism to survive by making it
less visible to its natural enemies. Camouflage is adaptive. Adaptation, however, is not
an isolated concept referring to only a few special properties of living things a it applies
to almost any part of the body. In humans, hands are adapted for grasping, eyes for
seeing, the alimentary canal for digesting food, legs for movement: all these functions
assist us to survive. Although most of the obvious things we notice are adaptive, not
every detail of an organism’s form and behavior is necessarily adaptive (Chapter 10).
Adaptations are, however, so common that they have to be explained. Darwin regarded
adaptation as the key problem that any theory of evolution had to solve. In Darwin’s
theory a as in modern evolutionary biology a the problem is solved by natural selection.
Natural selection means that some kinds of individual in a population tend to contribute
more offspring to the next generation than do others. Provided that the offspring
resemble their parents, any attribute of an organism causing it to leave more offspring
than average will increase in frequency in the population over time. The composition
of the population will then change automatically. Such is the simple, but immensely
powerful, idea whose ramifying consequences we shall be exploring in this book.
1.3 A short history of evolutionary biology
We shall begin with a brief sketch of the historic rise of evolutionary biology, in four
main stages:
1. Evolutionary and non-evolutionary ideas before Darwin.
2. Darwin’s theory (1859).
3. The eclipse of Darwin (c. 1880–1920).
4. The modern synthesis (1920s to 1950s).
..