If population density is rising, then land per capita is falling, leading to a loss of income, all else equal. Of course, the Boserup argument is that all else is not equal because households intensify production (increase output per hectare, <u>f</u> ~~)~~ . Thus the extent to which gross income per YY capita declines or rises depends on whether changes in gross income per capita compensate for LL declines in land per capita. But a second cause of ambiguous welfare effects is that welfare is better represented by net farm income, or gross income less costs. The intensification process involves an increase in a number of costs, including labor, oxen, modern inputs and land preparation (e.g. irrigation).

Increases in household welfare, where they occur, are often associated with diversification of agricultural production to a broader range of high value product that can be marketed through improving commercialization channels. Where rising population pressure and market access lead to increased specialization, and where agricultural technology adoption and input use increase, there may be a beneficial diversification into rural nonfarm activities.

In contrast to positive intensification processes, under very high population pressure and poor policy, institutional or agro-ecological environments, intensification could lead to involution and the diminution of economic and social well-being, and environmental degradation. Geertz (1963) characterized involution as a situation in which increasing demand for food is met by highly labor intensive intensification, but at the cost of very small and decreasing marginal and average returns to inputs. Because there still is relatively little landless labor in SSA, the extra work would often fall on family workers, rather than being supplied by landless workers, as in Asia. Of the 10 cases of very high population density in SSA studied by Turner et al. eds. (1993), there are signs of involution in the humid tropical areas of Imo State in Nigeria, and in the Usambara mountains of Tanzania, where special rules inhibit erosion control because it can jeopardize access to land for women.<sup>4</sup> Based on macro rather than micro data, Lele and Stone (1989) also suggest that a significant share of the intensification observed in SSA was already showing signs of involution by the mid-1980s. This means that the conclusions from aggregate data are more pessimistic than from case studies.

Heady and Stone (2014) find that agricultural intensities in much of African agriculture have reached the stage of permanent cropping. Most of the literature is consistent with the theory of intensification, both in Africa, as well as elsewhere. Baltenwick et al (2003), in an analysis of 48 sites in 15 countries of Africa, Latin America, and Asia, find that the forces of population density and market access transcend national and continental specificities and applied well across the study sites in all three continents. Their reviews, following McIntire et al (1992), focuses especially on crop-livestock integration and confirm the general trends and more detailed findings of these authors.

The papers in Pender et al. eds. (2006) study of strategies for sustainable farming systems in the East African Highlands focused primarily on low to medium potential areas. The selection of areas of lower agro-ecological potential also implies a bias in the results, this time against the BR effects, as in lower potential areas the work and investment incentives are likely to be lower than in higher potential areas. They find similar corroborating evidence for the general impacts, again with variations which will be discussed in subsequent sections of this paper. They emphasize that intensification is progressing especially well where vibrant markets are nearby. Much earlier this had been found to be true in a case study of the agricultural history of Machakos district in Kenya,

> 4 Women had secure access to unimproved land for their subsistence production, but once a parcel was improved via erosion control, would lose such access.

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