Biology Now, 2e

Whale Hunting ■ 203

all of the other landmasses of Earth had drifted

together to form one giant continent called

Pangaea. About 200 million years ago, Pangaea

slowly began to split up, separating to ultimately

form the continents as we know them. That

separation continues today; for example, each

year South America and Africa drift farther

apart by about an inch.

Birthplace of Whales

Earth’s continents are on massive tectonic plates,

which slowly move over time in a process called

continental drift or plate tectonics. About 250

million years ago, South America, Africa, and

A TG GC C CT G TG GA TG C GC C TC C TG CC CC T GC TG G CG C TG CT GG C CC TC T G

A TG GC C CT G TG GA TG C GC T TC C TG CC CC T GC TG G CC C TG CT C TT CC TC T G

Human

Mouse

TG GC C CT G TG G TG G T TG CC C T G G G CG G

G

C C C C C T C TG CT G C CC TC T G

C

A A C C

A TG GC C CT G TG GA TG C GC TC C TG CC CC T GC TG G TG C TG CT G C CC TC T G

Human

Chimpanzee

TG GC C CT G TG G TG G T TG CC C T G G G CG GG

G

A A C C C C C C C T C TG CT C CC TC T G

A TG GC T CT C TG GA T CC GA T CA C TG CC TC T TC TG G CT C TC CT T T CT T TT C

Human

Chicken

Chimpanzee insulin gene has

328/333 identical nucleotides to

human, a 98.4% sequence similarity.

Chicken insulin gene has 240/333

identical nucleotides to human, a

72% sequence similarity.

Mouse insulin gene has 276/333

identical nucleotides to human, an

83% sequence similarity.

Figure 11.13

DNA sequence similarities of the insulin gene

The complete coding sequence of the human insulin gene contains 333 nucleotides. Only the first

50 nucleotides are shown here. Unshaded paired sequences are identical nucleotides at that position;

those shaded in yellow are different.

Q1: If a sequence from another species showed a 96 percent sequence similarity to humans,

would that species be more or less closely related to humans than chimpanzees are?

Q2: Should similarities in the DNA sequences of genes be considered evolutionary homology?

Explain.

Q3: How is the increased similarity in the DNA sequences of genes between more closely

related organisms—and the decreased similarity between less closely related organisms—

evidence for evolution? Use the example in this figure to support your answer.