2.1 State and Development of the World's Genetic Diversity Center
13
outlining the zones of biodiversity on a global level. Six global diversity centers
with more than 5,000 species per 10,000 km 2 were identified; all were situated in
the humid tropics and subtropics: Choco-Costa Rica Center, Tropical Eastern
Andes Center, Atlantic Brazil Center, Eastern Himalaya-Yunnan Center, Northern
Borneo Center, New Guinea Center.
Although there was an increase in the number of flowering plant species over
the past 140 million years, the changes in the last 20,000 years were slight; the
extent of extinction of species was more significant than the amount of emerging
of new species (Signor, 1990).
2.1.2
Centers of Agrobiodiversity
The Russian botanist and geneticist N. I. Vavilov was the first to notice that
diversity within agricultural crops was not equally dispersed (Vavilov, 1926).
Vavilov defined the regions with the highest diversity within one crop as the
centers of diversity of crop plants. He assumed them to be the centers of origin of
that crop (now called "Vavilov's centers of origin"). He mapped out 8 major
centers: East Asia, Tropical Asia, South-western Asia, the Near East,
Mediterranean, Abyssinia, Andean, and Central America including South Mexico.
The continued geneflow between crops and their wild relatives in these areas
underpins their importance as sources of new variability. Different species of the
same crop, however, have been domesticated in different places 7 , or the
independent domestication of the same species of the crop occurred in various
places 8 (Harlan, 1976). Consequently, one single center of origin cannot be
identified for all relevant crops. Additionally, because of the evolutionary process
combined with human activities (Juma, 1989), secondary centers of diversity were
created (see Table 2.2), with significant variations to those from the centers of
origin (Harlan, 1971).
Zeven and Zhukovsky (1975) enlarged Vavilov's 8 centers of origin and
diversity by Harlan's secondary centers of diversity (Harlan, 1971) and drew the
mega-centers of cultivated plants to describe the origin and the main region of the
present diversity of the major crops on global level.
Although tropical forests are the areas singled out for rich biodiversity, the
drier ecosystems are far more important for crop resources, which are situated in
semi-arid and mountainous areas and are agriculturally marginal with respect to
soil fertility, water, and so forth (e.g., the Near East and Central Asia).
7
Different species of yams were domesticated in West Africa, Southeast Asia, and in tropical
America (Harlan, 1976).
• Both cassava and sweet potato were domesticated independently in Central and South
America (Harlan, 1976).
13
outlining the zones of biodiversity on a global level. Six global diversity centers
with more than 5,000 species per 10,000 km 2 were identified; all were situated in
the humid tropics and subtropics: Choco-Costa Rica Center, Tropical Eastern
Andes Center, Atlantic Brazil Center, Eastern Himalaya-Yunnan Center, Northern
Borneo Center, New Guinea Center.
Although there was an increase in the number of flowering plant species over
the past 140 million years, the changes in the last 20,000 years were slight; the
extent of extinction of species was more significant than the amount of emerging
of new species (Signor, 1990).
2.1.2
Centers of Agrobiodiversity
The Russian botanist and geneticist N. I. Vavilov was the first to notice that
diversity within agricultural crops was not equally dispersed (Vavilov, 1926).
Vavilov defined the regions with the highest diversity within one crop as the
centers of diversity of crop plants. He assumed them to be the centers of origin of
that crop (now called "Vavilov's centers of origin"). He mapped out 8 major
centers: East Asia, Tropical Asia, South-western Asia, the Near East,
Mediterranean, Abyssinia, Andean, and Central America including South Mexico.
The continued geneflow between crops and their wild relatives in these areas
underpins their importance as sources of new variability. Different species of the
same crop, however, have been domesticated in different places 7 , or the
independent domestication of the same species of the crop occurred in various
places 8 (Harlan, 1976). Consequently, one single center of origin cannot be
identified for all relevant crops. Additionally, because of the evolutionary process
combined with human activities (Juma, 1989), secondary centers of diversity were
created (see Table 2.2), with significant variations to those from the centers of
origin (Harlan, 1971).
Zeven and Zhukovsky (1975) enlarged Vavilov's 8 centers of origin and
diversity by Harlan's secondary centers of diversity (Harlan, 1971) and drew the
mega-centers of cultivated plants to describe the origin and the main region of the
present diversity of the major crops on global level.
Although tropical forests are the areas singled out for rich biodiversity, the
drier ecosystems are far more important for crop resources, which are situated in
semi-arid and mountainous areas and are agriculturally marginal with respect to
soil fertility, water, and so forth (e.g., the Near East and Central Asia).
7
Different species of yams were domesticated in West Africa, Southeast Asia, and in tropical
America (Harlan, 1976).
• Both cassava and sweet potato were domesticated independently in Central and South
America (Harlan, 1976).