Evolution And History

320 CHAPTER 13 | Human Adaptation to a Changing World

The Future of Homo sapiens

One of the difficulties with managing environmental and

toxic health risks is that serious consequences of new cul-

tural practices are often not apparent until years or even

decades later. By then, of course, these practices are fully

embedded in the cultural system, and huge financial in-

terests are at stake. Today, cultural practices, probably as

never before, are having an impact on human gene pools.

It remains to be seen just what the long-term effects on the

human species as a whole will be, but it is undeniable that

poor people and people of color bear a disproportionate

burden for these practices.

In addition to the problems human cultures are cre-

ating through changing the environment, new challenges

have blossomed from cultural advances. The values of

wealthy consumers living in industrialized countries

have spread to the inhabitants of poorer and developing

countries, influencing their expectations and dreams.

Of course, the resources necessary to maintain a luxuri-

ous standard of living are limited. Instead of globalizing

a standard of living that the world’s natural resources

cannot meet, it is time for all of humanity to use today’s

global connections to learn how to live within the carrying

capacity of the earth.

We are a social species with origins on the African

continent over 5 million years ago. Over the course of

our evolutionary history, we came to inhabit the entire

globe. From cities, to deserts, to mountain tops, to grassy

1930–51

50%

Human Sperm Concentration

% men with > 100 million sperm per ml

1951–60

44%

1961–70

28%

1971–80

21%

1981–90

16%

Figure 13.6 A documented decline in human sperm counts

worldwide may be related to widespread exposure to hormone-

disrupting chemicals.

Hormone disruptions may be at least partially responsible

for certain trends that have recently concerned scientists.

These range from increasingly early onset of puberty in

human females to dramatic declines in human sperm

counts. With respect to the latter, some sixty-one separate

studies confirm that sperm counts have dropped almost

50 percent from 1938 to 1990 (Figure 13.6). Most of these

studies were carried out in the United States and Europe,

but some from Africa, Asia, and South America show that

this is a worldwide phenomenon.

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