▶ Identify and evaluate the global impact of human biocultural evolution.
▶ Express the obligation everyone shares to be stewards of the earth and its plants, animals, and resources for the benefit of future generations.
- Based on your reading of this chapter as well as other materials outside of class, identify the most important consequences, both good and bad, of biocultural evolution for the future of our species. For each consequence you name, write a sentence that explains why it is important. Compare your list with that of your classmates and discuss the differences.
- Assess the impacts of human population growth on humans, other living things, and the earth over the past 10,000 years. Write a paragraph describing the obligations each of us shares to change these impacts. Compare your paragraph with that of your classmates and discuss the differences.
Australia’s Great Barrier Reef is a
UNESCO World Heritage Area, an
honor that places it on a par with other
sites of “outstanding universal appeal,”
such as the Statue of Liberty and the
Grand Canyon in the United States.
Its status as a world landmark aside,
the Great Barrier Reef is hurting. A
recent Australian government study
(Reef Water Quality Protection Plan
Secretariat, 2011) estimates that the reef
annually receives 34,000 tons of dissolved nitrogen from agricultural fertilizer runoff, about 62,000 pounds of
pesticides, and nearly 19,000,000 tons of
sediments (of which roughly 15,500,000
tons are the product of human activity).
Given these data, it is painfully obvious
that humans are killing the Great Barrier
Reef, not maliciously, not from indifference, but slowly and surely nevertheless. The Australian government recognizes the severity of the environmental
effects and is working to reduce humangenerated pollution of the reef. It will not
be an easy task.
The Great Barrier Reef illustrates an
important point about humans: We’ve
become rather dangerous to ourselves,
other living things, and the earth itself.
This textbook has given you the background needed to understand how and
why this happened. In Chapter 1, we
observed that modern humans are cultural and biological beings whose present and future reflect their past. But
where did we come from? And how did
we create the present? Answers to such
questions can help us understand some
of our strengths and limitations as a species and, if used wisely, inform decisions
that will affect our future.
Our story of the human past, which
we traced over 15 chapters, closes with
a look at some of the consequences of
biocultural evolution, perhaps the most
chilling of which is our new-found ability to trash the planet. We touch only
on a few key issues because the topic is
another textbook in itself. Our goal is to
impress upon you how unique our species has become and what this can mean
in practical terms for the quality of your
life, your children’s lives, and the wellbeing of the communities in which we
all live.
Human Success and the Anthropocene
Humans are the most successful species
ever to inhabit the earth. Sounds like
a wild claim, right? After all, there are
vastly more bacteria than humans, and
bacteria are literally everywhere, including inside of us! But it’s true. The earth
has never witnessed the rise of a species
quite like humans. The most telling measure of our success is that we humans
grew to be a major force of nature over
the last 10,000 years, and our global
impact accelerated greatly during the
past couple of centuries. Geologists and
other scientists are beginning to hammer
out a new concept, the Anthropocene,
the geological epoch during which
human behavior became one of the
earth’s major geomorphological and geological processes (e.g., see Crutzen, 2002;
The Economist, 2011). The Anthropocene
concept implies that millions of years
from now, long after humans have vanished from the scene, the record of our
brief existence will be a distinct geological formation, formed by a unique set
of processes that we largely created and
left indelibly stamped on the earth. Now
that’s success, perhaps in a blunt instrument sort of way, we admit, but no other
species can lay claim to the global effects
that we have already achieved, whether it be
our impact on the Great Barrier Reef, the
air we breath, or our next drink of water!
Consequences of Biocultural Evolution
We owe our success to biocultural
evolution and our primate ancestry.
Without them, all this would have never
happened. To explain why, let’s examine how our past informs our present
and future.
Hominins to the End of the Ice Age
Glimmers of our future success are not
easily found in the fossil record of our
australopith ancestors (see Chapter 9).
For millions of years, these hominins were just another primate on the
African savanna. If we had to point to
one thing that made them stand out
from their primate cousins, it was that
they walked erect on their two hind
limbs; they were bipedal. This peculiarity aside, the australopiths were successful in the same biological sense as any
other animal—they survived and successfully reproduced.
The game changer for our ancestors, whether they were australopiths
or early Homo, was our first rudimentary attempts at technological solutions
to problems between roughly 3 and 2.5
mya. This, along with the behavioral
changes that accompanied tool use,
launched an adaptive process that eventually became a distinctive part of the
life history strategy of early hominins.
The core components of hominin biocultural evolution took a long time to
develop. For hundreds of thousands of
years, we were tool-assisted hominins
living in small groups that were spread
thinly across the landscape. The rate of
biocultural change was so slow that a
thousand generations could pass, and
yet the tool kits of each succeeding generation looked basically the same. Even
after our ancestors began spreading
out of Africa into parts of Europe and
Asia around 2 mya (see Chapter 10), our
impact on animals, plants, and the earth
itself was negligible. There were too few
hominins on the ground, and they could
scarcely manage their own lives, much
less have a measurable environmental
impact on the regions in which they
lived. If any part of the human success
story can be said to be miraculous, it is
simply that hominins did not go extinct
during this, our training-wheel period as
a biocultural bipedal primate.
The archaeological record shows that
our Paleolithic ancestors were capable
of expanding into new habitats, largely
by adapting culturally. Nevertheless,
the rate of cultural evolution continued
its slow pace throughout the Lower
Paleolithic and much of the Middle
Paleolithic, while hominin population
density remained low everywhere (see
Chapter 11).
Things began to get a bit more complicated after about 200,000 ya with
the earliest appearance of anatomically
and behaviorally modern Homo sapiens in southern Africa (see Chapter 12).
Modern humans began spreading into
Asia and Europe after about 150,000 ya.
The rate of cultural changes also
increased at a faster pace; an Upper
Paleolithic hunter-gatherer might have
tools, huts, clothing, and even foods
that would have been unfamiliar to
his or her great-grandparents. Toward
the end of the Ice Age, around 12,000–
10,000 ya, Upper Paleolithic huntergatherers differed little in technology
and behavior from hunter-gatherer
groups that survived into the twentieth
century.
Throughout the past couple of million years, the lives of hunter-gatherers
and their predecessors weren’t easy or
disease-free. Our hominin ancestors suffered periodic food shortages that sometimes ended in starvation, and they certainly weren’t strangers to traumatic
injury and infectious disease. However,
hominin populations up to the beginning of early farming probably did not
suffer from epidemic diseases or from
such “crowd” infections as the common
cold. Because hunter-gatherer populations generally were small and mobile,
the reservoir of human hosts for harmful
viruses and bacteria wasn’t sufficient to
sustain itself in such groups.
For most of hominin history, our
ancestors’ reproductive capacity also
wasn’t much different from that of our
ape cousins. A woman who gave birth
every three or four years was probably typical of hominins up to just a
few thousand years ago. Infant mortality rates were high, as they continued
to be after the Ice Age for early farmers (and, regrettably, still are for some
communities).
Looking back, hominins had a pretty
good environmental record up to the
end of the Ice Age. According to the
archaeological record, it wasn’t because
our ancestors were natural conservationists who lived “in harmony with
nature.” If anything, it was simply
because there weren’t very many of us.
What mattered was that we had extraordinary potential as a species: Biocultural
evolutionary factors greatly enhanced our chances of biological success and
gave us exceptional flexibility in different habitats.
By the end of the Ice Age, there may
have been 5 million humans (Fig. 16-1),
or less than one person for every 10
square miles of land surface. It sounds
like very little, but it was sufficient for
some human groups to drive local populations of food animals to extinction or
nearly so. It also gives us a handy baseline against which to measure some of
the events that happened next.
Earliest Farmers and Cities
As we saw in Chapters 13 and 14, the
end of the last Ice Age marked a watershed moment in which we can find the
roots of the so-called Neolithic revolution. Domestication and agriculture
were the driving forces of this revolution, but the impact of Neolithic lifeways
went far beyond subsistence, and opinions differ as to the effects. The physiologist and popular writer Jared Diamond
(1987) bluntly refers to the invention of
agriculture as “the worst mistake in the
history of the human race.” At the other
extreme, Paul Colinvaux (1979), an eminent ecologist, expresses the same glowing perspective as archaeologist Graeme
Barker (see p. 349), calling agriculture
the “most momentous event in the history of life.”
Some researchers argue that human
population growth initiated the agricultural response; others see it happening the other way around. But there’s no
question that population size and density both tended to increase as farming produced larger and more predictable yields. World population doubled
in the 5,000 years after the end of the
Ice Age (see Fig. 16-1). In many places,
permanent villages and towns sprang
up surrounded by fields and pastures.
Sedentary living (which in many cases
began before agriculture) permitted
closer birth spacing, since mothers no
longer had to carry infants from camp to
camp, and the availability of soft cereal
grains for infant food allowed for earlier
weaning. Potentially, therefore, a woman
might bear more children. And they did.
Even very early Neolithic settlements,
such as Jericho in the Jordan River valley
and Çatalhöyük in Turkey (see Chapter
15), quickly reached considerable size. By
a.d. 1, world population had grown to
200,000,000, or roughly 3.5 persons per
square mile.
As agricultural techniques and
resulting harvests improved, surplus
production served as a kind of capital, or wealth, that stimulated new
kinds of socioeconomic interactions.
Some members of society also came to
fill specialized roles as priests, merchants, crafters, administrators, and
the like. A social and economic hierarchy of productive peasants, nonfarming
specialists of many kinds, and a small
but dominant elite emerged in a few
Neolithic state societies, or civilizations
(see Chapter 15).
Unlike hunter-gatherers, who
extracted their livelihood from available natural resources, Neolithic farmers
altered the environment by substituting
their own domesticated plants and animals for native species. Neolithic plowing, terracing, cutting of forests, draining of wetlands, and animal grazing
contributed to severe soil erosion and the
decline of many plant and animal species. Moreover, many of these practices
encouraged the growth of weeds and
created fresh habitats for crop- damaging
insects, malaria-bearing mosquitoes,
and other pests. Intensive agriculture
also depletes soil nutrients, especially
potassium. In the lower Tigris-Euphrates
Valley, high levels of soluble salts carried by irrigation waters slowly poisoned
the fields once farmed by Ubaidians and
Sumerians. In North Africa, Neolithic
herders allowed their animals to overgraze the fragile Sahara grasslands, furthering the development of the world’s
largest desert. These early farming practices left many areas so damaged that
they remained unproductive for thousands of years, until they could begin
to be reclaimed with the aid of modern
technology.
As with other biocultural aspects
relating to the development of food production, the effects on human health
were a mixed bag of benefits and costs.
As farming villages and towns grew
larger, infectious disease became prevalent (see Chapter 4). As you know, infectious diseases can cause epidemics, some
small, some catastrophic—for example,
the Black Death of the Middle Ages or
the worldwide influenza epidemic of
- They can potentially kill thousands
or even millions of people. Huntergatherer populations generally were little affected by infectious disease because
they lived in small mobile groups.
Farmers weren’t so lucky.
One major contributor to heightened
disease exposure came from close proximity of humans to domestic animals.
Many pathogens—including viruses,
bacteria, and intestinal parasites—can
be transferred from nonhuman animals to humans. For example, influenza
and tuberculosis can be transmitted to
humans by contact with some common
domesticated animals.
Several other significant human
diseases are associated with sedentism
and increasing population size and
density. Measles, for example, has been
shown to require a very large population
pool—in the thousands—to sustain itself
long-term (Cohen, 1989). So, measles
became prevalent only with the emergence of larger urban centers, making
it a “disease of civilization.” Likewise,
cholera is most commonly found in
urban contexts, especially where large
numbers of people share a common (and
contaminated) water source.
As if this list of diseases and potential human suffering isn’t enough, bioarchaeological studies have also shown
that overall health quality declined with
the development of agriculture (Cohen
and Armelagos, 1984; Steckel and Rose,
2002). Essentially, our ancestors had
traded the uncertain possibility of starvation as a hunter-gatherer for probable
malnutrition as a farmer. If it seems paradoxical that average health was declining among food producers at the same
time that populations were expanding,
that’s because it is. As one researcher
commented, “Although humans became
physically worse-off in marked respects,
they also became more numerous. The
agricultural age made possible far denser
populations, but less healthy ones than
ever before. Historians, anthropologists,
and others concerned with this apparent
paradox are still exploring its implications in detail” (Curtin, 2002, p. 606).
Nevertheless, even with greater
exposure to disease pathogens and other
health risks associated with living in
denser populations, the health picture
for early farmers wasn’t all that bleak.
After all, it’s ultimately our success
as a species (that is, more people) that
helped infectious pathogens to be more
successful. The advent of farming and
the emergence of the earliest civilizations were important components of
humankind’s success.
Industrial Revolution
to the Present
Chapter 15 finished this textbook’s story
of biocultural evolution with a recounting of the earliest civilizations and the
beginning of written history. But by ending the story there, we left a particularly
important (and environmentally devastating) part of the human story untold.
A graph of world population growth
makes the point best (see Fig. 16-1).
During the past couple of centuries, we
humans began to be far more successful
as a species than is good for us and the
planet. By the year 1800, the Industrial
Revolution was well under way, and
world population approached 1 billion,
or about 18 persons per square mile.
Two centuries later, by the year. 2000, we
achieved a staggering 105 persons per
square mile of every bit of dry land on
earth. The current birth rate is such that
we now add roughly 10,000 new mouths
to feed every hour, 24 hours a day, 7 days
a week.
Although we chose the Industrial
Revolution as our point of departure in
this section, no single factor explains
the dangerously accelerating growth of
world population over the past few hundred years. The growth rate also is not
equally distributed among nations. The
most recent United Nations report on
world population notes that 95 percent
of population growth happens in developing countries. Likewise, resources
are not distributed equally among all
nations. Only a small percentage of the
world’s population, located in a few
industrialized nations, control and consume most of the world’s resources. A
2009 study estimated that 48 percent
of the world’s population exist on less
than $2 per day (Population Reference
Bureau, 2009).
As biologists can tell you, a natural
population growth function similar to
the one plotted in Figure 16-1 is unsustainable, regardless of whether we’re
talking about E. coli bacteria or humans.
It is pointless to hope that humans will
somehow be the lucky exception to the
rule. Dying coral reefs, algal blooms
in our lakes, pesticides in our drinking water, air pollution levels that kill
the elderly and weak in our cities, rapid
melting of the polar ice—all these things
are nature’s way of telling us to slow
down, control our growth rate, and
actively work toward a brighter and
more sustainable future for our children
(Fig. 16-2). If we can’t or won’t change,
then nature can make the point more
bluntly (for example, a global pandemic
of a deadly disease like Ebola), and common sense tells us that we don’t want to
go there.
Today, the earth’s human population still relies for food primarily on the
seeds of just a half dozen grasses (wheat,
barley, oats, rice, millet, maize), several
root crops (potatoes, yams, manioc), and
a few domesticated fowl and mammals
(in addition to fish). Because of their relative genetic similarity, these domesticated species are susceptible to disease,
drought, and pests. Agricultural scientists are trying to prevent potential
disaster by reestablishing some genetic
diversity in these plants and animals
through the controlled introduction of
heterogeneous (usually “wild”) strains.
A few farmers have also rediscovered
the benefits of multicropping—interspersing different kinds of crops in a single agricultural plot. Combining grains,
root crops, fruit trees, herbs, and plants
used for fiber or tools mimics the natural
species diversity and reduces soil depletion and insect infestation. The challenge
farmers face is to make environmentally
friendly approaches like multicropping
scalable, such that they are technologically and economically feasible to meet
world food demands.
Global Climate Change
At the global level, the biggest environmental problem we currently face concerns climate change, sometimes also
called “global warming.” This phenomenon has been researched for more than
three decades by thousands of scientists.
So, there’s a lot of information out there.
Unfortunately, there’s also a good deal of
misinformation.
Throughout this book, we have
emphasized that science is an approach
based on data collection, hypothesis testing, generalization, and verification. We
have shown that scientific investigation
typically can be a long process and one
that frequently involves debate regarding alternative approaches and conclusions. It’s important to recognize that
science advances as these debates occur
in the pages of scientific journals and at
organized scientific meetings. Little is
gained by uninformed, ideology-driven
claims coming from television commentators or from politicians in the heat of
partisan disputes.
Given all the accumulated scientific
data and decades of analysis within the
scientific community, there are no major
disagreements on two major points:
- Rapid global climate change has
been occurring and continues to
occur, including marked warming of
the earth’s atmosphere and acidification of the world’s oceans (threatening habitats like the coral reefs that
we mentioned earlier). - Human activity in the last two centuries is the most significant cause of
this climate change.
As many of you know, humans have
caused these changes as a result of the
burning of fossil fuels—that is, coal
and petroleum products. This burning
leads to about 10 billion tons of carbon
dioxide emissions into the atmosphere
every year. Along with other “greenhouse gases,” such as methane, these
products trap heat in the atmosphere. In
turn, the increased heat leads to melting of polar ice, raising of sea levels, and
major impacts on weather, including
intensification and greater unpredictability regarding droughts, flooding, and
hurricanes.
What’s more, the vast majority of
countries and their leaders recognize
that global climate change is a very serious and urgent problem. The United
Nations has organized two extraordinary international conferences specifically to take global action. The first of
these took place in 1997 in Kyoto, Japan,
and as of 2011, its agreements were ratified by 194 countries; the only major
country that failed to sign on was the
United States.
The second conference was held in
December 2009 and was attended by
representatives of 192 countries, including 60 world leaders. Much anticipation
and hopes for building on and strengthening the earlier Kyoto agreements preceded the conference. Unfortunately,
and to the collective disappointment
of most of the world, even less resulted
from this meeting. Another such attempt
won’t take place until 2014, at the earliest. Meanwhile, humans pour increasing
amounts of greenhouse gases into the
atmosphere.
Learning from the Past and Facing an Uncertain Future
Throughout this textbook, we’ve tried
to draw your attention to some of the
costs and benefits of biocultural evolution, especially those relating to overall
human health. As the evidence shows,
the rate of cultural changes increased in
a manner like that of the world population (see Fig. 16-1), and the effects of
increasing cultural changes and population growth are inseparably intertwined.
Biologically, however, most humans
are still well adapted to being huntergatherers, not suburban, pizza-eating
couch potatoes. And in some ways, our
bodies haven’t even adjusted to the fact
that thousands of years ago, many of our ancestors became farmers. These problems are easier to understand if you
view them in the context of biocultural
evolution.
Some people, even some scientists,
claim that the costs of these changes
outweigh the benefits. Others feel just
as strongly that the opposite is true.
Regardless of the perspective you take
about the effects of biocultural evolution, whether you see our future as rosy
or depressing, there’s no going back.
The world we live in is the cumulative product of remarkable contributions made over millions of years by
our ancestors who became the first tool
users, crossed over into the next valley
to see what was there, mastered the use
of fire, invented the first composite tools
and projectile weapons, domesticated
the dog, learned to navigate by the stars,
raised the first crop, invented the first
printing press, and, yes, even invented
the cell phone. Without the benefit of
their hard work, sacrifices, and brilliant
insights, most of us wouldn’t be here
at all. There would be no cities, no art,
no educational institutions, no writing,
no books—meaning, of course, no textbooks and exams either. And for all the
extremely serious damage that can be
traced back to our increasing population density over the past few millennia
(and particularly over the past couple
of centuries), the effects of biocultural
evolution, at least in the developed
world, also doubled the average modern
human life span and brought us affordable mass transportation, high-tech
communication and entertainment, and
a diverse and easily obtainable assortment of foods, clothing, and shelters.
Our challenge, and one that we will
bequeath to subsequent generations, is
to identify and repair the damage that
we’ve caused along the way and to learn
how to make things better for all living
things and the earth itself.