Genetic Resources in Agroecosystems - Agroecology: The Ecology of Sustainable Food Systems - page 183

14 Genetic Resources in

Agroecosystems

Agriculture came about as early human cultures intensi-
fied their use and care of particular plants and animals
that they found to be of value. During this process, humans
inadvertently selected specific traits and qualities in these
useful organisms, altering their genetic makeup over time.
Their ability to produce edible or useful biomass was
enhanced, but their ability to survive without human inter-
vention was reduced. Humans came to depend on these
domesticated species for food, feed, and fiber, and most
of them became dependent on us.
Throughout most of human history, humans manipulated
the genetic makeup of crops and livestock without explicit
knowledge of genetics. Farmers simply made the choice to
plant seed or breed animals from the individuals or popula-
tions that demonstrated the most desirable characteristics, and
this was enough to direct the evolution of domesticated spe-
cies (Figure 14.1). Gradually, plant and animal breeding
developed into a science as we learned more about the genetic
basis of selection and began to direct it more specifically to
our advantage. Today, the fields of biotechnology and genetic
engineering are rapidly changing the way humans manipulate
the genes of domesticated species, making it possible to
incorporate traits and characteristics into plants and animals
in ways and at rates never before possible.
But from the viewpoint of sustainability, the direction
of crop and livestock breeding efforts of the past several
decades — and the directions proposed for the future —
are causes for deep concern. The genetic base of agricul-
ture has narrowed to a dangerous point as human societies
have become increasingly dependent on a few species of
food-producing organisms and on a smaller number of the
genes and genetic combinations found in those species.
Crop plants have lost much of the genetic basis of their
pest and disease resistance and their ability to tolerate
adverse environmental conditions, leading to crop failures
and increased dependence on human-derived inputs and
technologies for the maintenance of optimum growth con-
ditions. In addition, genetic resources beyond the crops
themselves — wild crop relatives, weedy derivatives, and
traditional cultivated varieties, genetic lines, and breeding
stocks — have been greatly reduced.
The relationship between genetics and agriculture is
a vast topic. This chapter explores a small part of it,
focusing on the foundations needed for understanding the
role of genetic diversity in moving toward sustainability
in agriculture. We examine genetic change in nature and

how it results in genetic diversity, outline the processes
humans use to direct and manipulate genetic change in
domesticated species (with a focus on crop plants), and
then discuss how genetic resources eventually need to be
managed at the whole agroecosystem level. The important
social and economic issues concerning crop and livestock
breeding and control of access to genetic material are
addressed in the recommended readings at the end of
this chapter.

GENETIC CHANGE IN NATURE AND THE
PRODUCTION OF GENETIC DIVERSITY

From the perspective of geologic time, the earth's flora
and fauna are constantly changing. The physical and
behavioral characteristics of species change, new species
appear, other species go extinct. This change, called evo-
lution, is made possible by the manner in which traits are
passed from parent to offspring and is driven by changes
in environmental conditions. As ice ages come and go,
continents move, and mountains emerge and erode, living
things respond. Through natural selection, the changing
and varied environment acts on species' genomes, causing
them to change from generation to generation.
Natural selection has created the genetic diversity
found in nature, the raw material that humans have worked
with in domesticating plants and animals and creating
agroecosystems. It is therefore important to understand
how natural selection works and how it applies to human-
directed genetic change and the maintenance of our
agricultural genetic resources.

A DAPTATION

The concept of adaptation is a basis for understanding
natural selection because it relates the environment to a
species' traits. The term refers both to a process and to
a characteristic resulting from that process. In static
terms, an adaptation is any aspect of an organism or its
parts that is of value in allowing the organism to with-
stand conditions of the environment. An adaptation may
be as follows:

• enable an organism to better use resources

• provide protection from environmental stresses

and pressures

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