Biology Now, 2e

Whale Hunting ■ 193

group of organisms over generations. Whales, for

example, evolved from four-legged land-living

animals into sleek emperors of the ocean, slowly

becoming suited for the water over tens of millions

of years. Whales changed as a population. Popula-

tions evolve; individuals do not.

You may wonder how we can be sure of evolu-

tionary change, especially for a transformation

as extreme as that of a furry, four-legged beast

into a whale. There is strong evidence for evolu-

tion not only from fossils like those that Thewis-

sen studies, but also from features of existing

organisms, common patterns of how embryos

develop, DNA evidence, geographic evidence,

and even direct observation of organisms evolv-

ing today—including man’s best friend.

Artificial to Natural

As we saw in Chapter 7, all dogs are a single

species. That species is Canis lupus familiaris,

a subspecies of the gray wolf. Scientists estimate

that domestication of the gray wolf began about

16,000 years ago as humans habituated the

animals to civilization. From there, people bred

the wolf for desired qualities, such as decreased

agression and the ability to follow commands.

Millennia later, dogs were selectively bred for

specific traits like the long legs of a greyhound

or the short snout of a bulldog. This selective

process has led to incredible variation in the size

and shape of dog breeds, from 6-pound Chihua-

huas to 200-pound Great Danes (Figure 11.3).

Dogs are an example of evolution that we can

directly observe, and they evolved via artificial

selection. Artificial selection is brought about

by selective breeding, in which humans allow

only individuals with certain inherited charac-

teristics to mate.

Through selective breeding, humans have

crafted enormous evolutionary changes within not

only dogs, but many other domesticated organ-

isms, including ornamental flowers, pet birds, and

food crops. We can observe evolution happening

through artificial selection via selective breeding.

Artificial selection happens when humans

choose which individuals of a particular species

are allowed to breed. Without the interven-

tion of humans, can the environment itself

Figure 11.2

A montage of

mammals

Earth boasts an

amazing diversity of

life, as evidenced here.

These are only a few

of the almost 5,500

species of mammals

currently living on the

planet.