Biology Now, 2e

202 ■ CHAPTER 11 Evidence for Evolution

EVOLUTION

with chickens, for whom the DNA sequence of

the same gene is only 72 percent identical to

ours. In fact, the insulin gene of our closest

living relative on Earth, the chimpanzee, has

98 percent similarity to the human insulin

gene. That comparability implies that humans

and chimpanzees share a very recent common

ancestor.

The fact that these separate lines of

evidence—anatomical features and DNA—

yield the same result over and over again for

diverse groups of organisms is strong evidence

for evolution.

Whale evolution is “one of the best case stud-

ies documenting how a vertebrate can go from a

terrestrial to an aquatic environment,” says Lisa

Cooper. Another type of evidence supporting

whale evolution comes from the locations where

whale fossils have been found.

closely related to even-toed ungulates—a group

of hoofed mammals that includes modern deer,

giraffes, camels, pigs, and hippos. Indohyus

is an example of an extinct even-toed ungu-

late. Molecular studies therefore confirm the

prediction that whales and Indohyus share a

common ancestry.

According to DNA sequence similarity,

hippos are whales’ closest living relatives.

Whale DNA is more similar to hippo DNA

than to the DNA of other marine mammals,

such as seals and sea lions. DNA sequence

similarity is a measure of how closely related

two DNA molecules are to each other. For

example, in the DNA sequences of the same

insulin gene in humans and mice, 83 percent

of the nucleotides are identical at correspond-

ing positions (Figure 11.13). We share a more

recent common ancestor with mice than we do

Figure 11.12

Vestigial traits are reduced or degenerated remnants with no apparent function

Snakes are limbless reptiles with no apparent use for the degenerated remnants of hind legs that

they still have. The python shown here has extremely reduced hind legs that are only barely visible

externally. M

Q1: Why are vestigial structures among organisms evidence for evolution? Give an example of

another vestigial structure.

Q2: Are vestigial structures also homologous structures? Explain.

Q3: Why do vestigial structures still exist if they are no longer useful?

Reduced

hind legs

External surface Skeletal structure