The use of sweet potato as fodder in the central highlands of New Guinea [CHNG] led to a substantial increase of a previously small pig herd. This, in turn, caused changes in habitat and social arrangements. Where pigs are mutually exchanged, the expansion of pig production in some part of a network leads to expanding production in other parts. This is termed the Jones effect. Since the CHNG were only discovered some 50 yr ago, this effect is an excellent opportunity to study human ecology in change.