194 ■ CHAPTER 11 Evidence for Evolution
EVOLUTION
become more common in successive generations
because they have produced more offspring.
For example, in 1977 a terrible drought struck
the Galápagos Islands off the coast of Ecuador.
One species of small ground finches—petite
birds with sharp, pointy beaks—starved as the
small, tender seeds they ate became scarce. But
some heat-loving, drought-resistant plants still
produced large, hard seeds. The finches with
larger beaks could eat those seeds. They survived
and reproduced, and by 1978, in just one genera-
tion, the average beak size in the population had
increased (Figure 11.4).“choose” who survives and breeds? It does. In
nature, evolution occurs mainly via natural
selection, as well as through other mechanisms
we will discuss later. Natural selection is the
process by which individuals with advanta-
geous inherited characteristics for a particular
environment survive and reproduce at a higher
rate than do individuals with other, less useful
characteristics. In other words, whoever has
the most kids wins!
After the environment “chooses” the
winners—those that successfully breed the
most—the characteristics of those individualsGray wolf
(common ancestor)European
toy dogsScent
houndsSight
houndsOriental
toy dogFeral
dogsNative
American dogsChow
chowArctic
spitzTerriers MastiffsPug Asian Dingo Borzoi Gun dogs Spaniels
pariah dogsAfghan
houndGreat
DaneSaint
BernardBulldogEurope North America China IndiaFigure 11.3
Selective breeding of dogs produces myriad traits
Dogs were domesticated only a few times, and always from gray wolves. Thus, the remarkable diversity of dogs represents the
effects of selective breeding on a small number of lineages of domesticated wolves.
Q1: What is selective breeding, and how does it work?Q2: Explain how selective breeding leads to artificial selection.Q3: Name as many organisms as you can whose current characteristics are due to artificial selection.