The human transport of animals across the Northern Atlantic 217 



transformed into weeds. They were of course accompanied by insects and other 

 lower animals feeding upon or otherwise connected with them. 



Eventually civilization based on agriculture moved westward, forested land 

 around the Mediterranean was developed into culture-steppe occupied by culti- 

 vated plants but also by weeds. Locally, primary steppe of this region contributed 

 a number of additional weeds, with adherent vermin. 



During the Roman age, about the beginning of our chronology, the modern 

 colonization of Central Europe started, then slowly spread northward. The first 

 permanent glades were cut out of the continuous forest carpet and invaded, with 

 the aid of man, by cultivated plants— and weeds. Thus the culture-steppe con- 

 quered Europe, "step by step", the isolated patches of arable land increased and 

 fused together. Already at the time of Columbus the coastland of Western Europe 

 was almost devoid of forests and transformed into an artificial steppe inhabited 

 by man's constant followers among plants and animals, invited or selfinvited. They 

 were all ready to embark the ships and, if the voyage was favourable, to settle 

 wherever they landed in a suitable climate, provided man had prepared the soil. 

 Similar views, concerning the synanthropic bird fauna, have been express ed by 

 Lack (1954, p. 200-202). 



How different were conditions on the American side when transatlantic trade 

 was starting! — The high Indian cultures, founded upon agriculture, were restricted 

 to Central America and parts of the Andes farther south. In northeastern North 

 America, at least, the tribes were more or less migratory and had hardly progressed 

 beyond the neolithic stage. A very primitive form of agriculture, with maize and 

 beans as foremost plants, was practiced by the Iroquois in the St. Lawrence 

 valley (Coleman, 1930, p. 11). Farther south within the limits of the present U.S.A., 

 also along the Atlantic coast, agriculture seems to have been carried on more in- 

 tensively and sweet potatoes, tobacco, cotton, sunflower, &c., were cultivated. 

 But nowhere was the plow used. The general custom was to burn over the ground 

 and to plant some grains of maize &c. into holes dug at short distances with the 

 aid of primitive shovels, hoes or spades (Hodge, 1907, p. 24-27). Nothing like the 

 arable land of the contemporaneous Eastern Hemisphere was produced in this way 

 and though some tribes planted corn in the same spots from year to year, the culti- 

 vation of the soil seems generally to have been of a more or less casual character, 

 except among the Pueblos of the present New Mexico and Arizona, where agricul- 

 ture was the dominating trade, based on irrigation. 



Therefore, in North America, the chance of native steppe plants invading per- 

 manent arable land and transforming into constant weeds was considerably less 

 than in the Old World. This holds true especially for northern coastal districts, 



