Page 71 - Environment: The Science Behind the Stories

areas would sometimes fly into death zones. Today, thousands
of honeycreepers from mountain forests die each year when Great Collie
they fly downslope and are bitten by malarial mosquitoes. As Dane
environmental conditions vary in time and space, adaptation
becomes a moving target.
Chihuahua Saint Bernard

FaQ Isn’t evolution based on just one man’s
beliefs?
Because Charles Darwin contributed so much to our early
understanding of evolution, many people assume the con-
cept itself hinges on his ideas. But scientists and laypeople
had been observing nature and puzzling over fossils for a long
time, and the notion of evolution was being discussed long (a) Ancestral wolf (Canis lupus) and derived dog breeds
before Darwin. Once he and Alfred Russel Wallace indepen-
dently proposed the concept of natural selection, scientists
finally gained a precise and feasible mechanism to explain
how and why organisms change across generations. Later,
geneticists discovered Gregor Mendel’s research and worked Cabbage Broccoli
out how traits are inherited—and modern evolutionary biol-
ogy was born. Twentieth-century scientists Fisher, Wright,
Dobzhansky, Simpson, Mayr, and others ran experiments and
developed sophisticated mathematical models, documenting Brussels Cauliflower
phenomena with extensive evidence and making evolution- sprouts
ary biology into one of science’s strongest fields. Since then,
evolutionary research by thousands of scientists has driven
our understanding of biology and has facilitated spectacular
advances in agriculture, medicine, and biotechnology.

(b) Ancestral Brassica oleracea and derived crops
Evidence of selection is all around us Figure 3.4 Selective breeding, or artificial selection, has

The results of natural selection are all around us, visible in resulted in our many breeds of dogs and varieties of crops.
every adaptation of every organism. In addition, scientists With dogs (a), we began with the gray wolf (Canis lupus) as the
have demonstrated the rapid evolution of traits by selection ancestral wild species, and by breeding like with like and select-
ing for the traits we prefer, we have produced breeds as different
in countless lab experiments, mostly with fast-reproducing as Great Danes and Chihuahuas. By this same process we have
organisms such as bacteria, yeast, and fruit flies. created our immense variety of crop plants (b). Cabbage, brussels
The evidence for selection that may be most familiar sprouts, broccoli, and cauliflower were all generated from a single
to us is that which Darwin himself cited prominently in his ancestral species, Brassica oleracea.
work 150 years ago: our breeding of domesticated animals.
In domesticated dogs, cats, and livestock, we have conducted millennia (Figure 3.4b). Through selective breeding, we have
selection under our own direction. We have chosen animals created corn with bigger, sweeter kernels; wheat and rice
with traits we like and bred them together, while not breed- with larger and more numerous grains; and apples, pears, and
ing those with variants we do not like. Through such selective oranges with better taste. We have diversified single types into
breeding, we have been able to augment particular traits we many—for instance, breeding variants of the plant Brassica
prefer. oleracea to create broccoli, cauliflower, cabbage, and brussels
Consider the great diversity of dog breeds (Figure 3.4a).
People generated every type of dog alive today by starting sprouts. Our entire agricultural system is based on artificial
selection. We depend on a working understanding of evolution
with a single ancestral species and selecting for particular for the very food we eat.
desired traits as individuals were bred together. From Great
Dane to Chihuahua, all dogs are able to interbreed and pro-
duce viable offspring, yet breeders maintain striking differ- Evolution generates biodiversity
ences among them by allowing only like individuals to breed
with like. This process of selection conducted under human Just as artificial selection helps us create new types of pets,
direction is termed artificial selection. farm animals, and crop plants, natural selection serves to
Artificial selection has given us the many crop plants we elaborate and diversify traits in wild organisms. Over the long
depend on for food, all of which people domesticated from term, natural selection helps lead to the formation of new spe-
70 wild ancestors and carefully bred over years, centuries, or cies and whole new types of organisms. Life’s complexity can

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