Whale Hunting ■ 195
Six lines of evidence provide compelling
support for biological evolution:
- Direct observation of evolution through arti-
ficial selection - Fossil evidence
- Shared characteristics among living organisms
- Similarities and differences in DNA
- Biogeographic evidence
- Common patterns of embryo development
Nowhere is all this evidence more present and
intriguing than in one of the most dramatic tran-
sitions to occur on Earth: the evolution of small,
land-living mammals into dolphins, porpoises,
and mighty whales.
Fossil Secrets
Fossils are the mineralized remains of
formerly living organisms or the impressions
of formerly living organisms (Figure 11.5).
For Thewissen, getting his hands on the
This is one of many examples of how a popula-
tion can evolve via natural selection so that more
and more individuals have beneficial traits, and
fewer and fewer have disadvantageous traits.
This is called adaptation—an evolutionary
process by which a population becomes better
matched to its environment over time. The finch
population quickly adapted to its new, drier envi-
ronment. Over time, the small-beaked finches
died off and the large-beaked birds survived and
reproduced; the finch population adapted to its
environment in just a few years. Other adapta-
tions take millions of years, such as whale ances-
tors adapting to aquatic life.
It is important to realize that biological evolu-
tion includes human evolution. Surveys taken
since 2013 reveal that about 40 percent of adults
in the United States do not believe that humans
evolved from earlier species of animals. This
statistic is startling because evolution has been
a settled issue in science for nearly 150 years.
Scientists like Thewissen go to work every day
and see evolution in action. In fact, the vast
majority of scientists of all nations agree that the
evidence for evolution is overwhelming.
Birds with smaller beaks were less likely to
find seeds to eat and died at higher rates,
thus failing to have sex, produce offspring,
and pass on their genetic traits.
Birds with large beaks were
more likely to survive, and
passed on their large beak
size to their offspring.
Figure 11.4
Natural selection results in larger beak size in finches
After a drought, only birds with larger beaks were able to eat the available food: large, hard seeds. In the
span of just one generation, the average size of the species’ beak was visibly larger.
Q1: What is natural selection?
Q2: If heavy rains caused an abundance of small, tender seeds and fewer large seeds, what do
you predict would happen to the average beak size of the finches?
Q3: Compare and contrast artificial selection and natural selection. Name two ways in which
they are similar. How are they different?