Evolution, 4th Edition

588 CHAPTER 22

make indispensable contributions to conservation efforts. They use phylogenetic

information to determine where potential nature reserves should be located to

protect the greatest variety of biologically different species; they use evolutionary

biogeography to identify regions with many endemic species (e.g., Madagascar);

they use genetic methods and theory to prevent inbreeding load in rare species

and to distinguish genetically unique populations [3, 44]; and they use genetic

markers to identify illegal traffic in endangered species (see [8]).

Climate change is real and is being caused by humans. (See Climate Change:

Evidence and Causes, written for a general audience by the world’s most prestigious

scientific assemblies [110].) Evolutionary biologists are increasingly concerned

with the risk of species extinction due to climate change. Their studies range from

analyses of shifts in species geographic ranges in the past, to genetic variation and

other factors that will determine the likelihood of evolutionary adaptation [69, 109,

115]. Some researchers offer a more optimistic outlook than others, at least for

certain kinds of species in some parts of the world, but all agree that more research

is urgently needed.

times faster than niche evolution has typically been in the

past, in order to keep pace [96]. There is already evidence

that many species will shift their ranges instead of geneti-

cally adapting, but such shifts are difficult or impossible for

most mountaintop and Arctic species, and for many others

that lack the habitat “corridors” along which they might dis-

perse. (Most forest-dwelling species, for example, will not

disperse through cities or cornfields.) Computer simulations,

based on various scenarios of warming rate and species’

capacity for dispersal, suggest that within the next 50 years,

between 18 and 35 percent of species will become “com-

mitted to extinction”—that is, they will have passed the point

of no return [111].

If mass extinctions have happened naturally in the past,

why should we be so concerned? Different people have

different answers, ranging from utilitarian to aesthetic to

spiritual. Some point to the many thousands of species that

are used by humans throughout the world today, ranging

from familiar foods to fiber, herbal medicines, and spices.

Others cite the economic value of ecotourism and the enor-

mous popularity of bird-watching in some countries. Biolo-

gists will argue that thousands of species may prove useful

(as many already have) as pest control agents or as sources

of medicinal compounds or industrially valuable materials.

Except in a few well-known groups, such as vertebrates

and vascular plants, most species have not even been

described, much less been studied for their ecological and

possible social value.

The rationale for conserving biodiversity is only partly

utilitarian, however. Many people (including the authors)

cannot bear to think that future generations will be de-

prived of tigers, sea turtles, and macaws. They share with

millions of others a deep renewal of spirit in the presence

of unspoiled nature. Still others feel that it is in some sense

cosmically unjust to extinguish, forever, the species with

which we share Earth.

Conservation is an exceedingly complicated topic; it re-

quires not only a concern for other species, but compassion

and understanding of the very real needs of people whose

lives depend on clearing forests and making other uses of

the environment. It requires that we understand not only

biology, but also global and local economics, politics, and

social issues ranging from the status of women to the reac-

tions of the world’s peoples and their governments to what

may seem like elitist Western ideas. Anyone who undertakes

work in conservation must deal with these complexities. But

everyone can play a helpful role, however small. We can try

to waste less; influence people about the need to reduce

population growth (surely the most pressing problem of all);

support conservation organizations; patronize environment-

conscious businesses; stay aware of current environmental

issues; and communicate our concerns to elected officials at

every level of government. Few actions of an enlightened

citizen of the world can be more important.

BOX 22B

The Current Extinction Crisis (continued)

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