19
Methods
Where not adequately specified in the main text, measurement of variables in the analysis was
as follows. All series are available from the corresponding author.
Geography
Geography is one hundred times the average of three constituent variables after each
was normalized (0,1] by division of its maximum value in the N=112 country sample.
Geography therefore varies
(
)
0,100
. The constituents are: (1) Climate as measured by a four
point scale based of the Köppen classification and ordered in ascending value according to
how favorable conditions are to agriculture: 1=dry tropical or tundra and ice, Köppen
classification B and E. 2=wet tropical, Köppen classification A. 3=temperate humid
subtropical and temperate continental, Köppen classification Cfa, Cwa and D. 4=dry hot
summers and wet winters, Köppen classification Csa, Csb, Cfb and Cfc, which is particularly
favorable to annual heavy grasses. The data were obtained from Strahler and Strahler
26
. (2)
Latitude as measured by the absolute distance from equator in latitude degrees. The data are
from the World Bank
27
. (3) East-West orientation of axis as measured by the distance in
longitudinal degrees between the eastern and westernmost points of each continent and
dividing this number by the distance in latitudinal degrees between the northernmost and
southernmost points.
Biogeography
Biogeography
( )
n
A
% is one hundred times the average of Plants and Animals after each
was normalized (0,1] by division of its maximum value. Plants denotes the number of annual
or perennial wild grasses known to exist in pre-history with a mean kernel weight exceeding
10 milligrams. The data are from Blumler
11
. The geographical distribution ranges between 33
species in the Near East, Europe, and North Africa to 0 in the Pacific islands. Eurasia was
divided into three subcontinents that had different and independent experiences of plant and
animal domestication. The Western part reaches its limit in the Indus Valley in Pakistan,
where the easternmost archeological evidence of crops from the Fertile Crescent have been
found
13
. Southeast Asia includes Indonesia, the Philippines, and Papua-New Guinea. America
was split up into three zones of independent agricultural origins; Central, North, and South.
Caribbean islands and islands near Africa are regarded as belonging to the Central American
and African zones respectively, while the Pacific islands (which are not in the sample
analysed) are independent of the Asian zone of agricultural origin and hence had zero species
suitable for domestication.
Convention