Biology Now, 2e

Whale Hunting ■ 195

Six lines of evidence provide compelling

support for biological evolution:

1. Direct observation of evolution through arti-
   ficial selection


2. Fossil evidence


3. Shared characteristics among living organisms


4. Similarities and differences in DNA


5. Biogeographic evidence


6. 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?