ture droughts but also the degree of inequality in the region (Basu, 1986).

     These sometimes desperate tradeoffs between different components of the resource endowment illustrate why simple or short-term definitions of poverty, hunger and food security provide an incomplete understanding of household's livelihood strategies. They have important implications for economic sustainability, which we will explore in the next subchapter. They also have important implications for environmental sustainability and social equity.

Economic dimensions of sustainability

Sustainability, like food security, has been defined in many ways. The Brundtland Commission (WCED, 1987) defined sustainable development as "development that meets the needs of the present without compromising the ability of future generations to meet their own needs." But even such an intuitively appealing definition raises difficult operational questions regarding both needs and ability (Serageldin, 1996). Abilities depend on the resources that individuals and households have at their disposal, and the ways in which they can be combined and exchanged to produce goods and services that they desire.

     Sustainability can, in turn, be understood in terms of maintaining or increasing a household's ability to produce desired goods and services-which may or may not involve maintaining or increasing the level of each particular component of the household's resource endowment. A very narrow interpretation of sustainability involves maintaining each component of the resource endowment at its current level or higher. In its strictest sense this would mean that non-renewable resources could not be used at all, and that renewable resources could be used only at rates less than or equal to their growth rates. Such a requirement would preclude extraction of oil to improve human capital, for example by investing in education for girls (Serageldin, 1996). A broader interpretation of sustainability by contrast, involves maintaining the total stock of capital at its present level or higher, regardless of the mix of different types of capital. This would require the unrealistic assumption that different types of capital can be substituted completely for one another, and that complete depletion of one type is acceptable as long as it is offset by a sufficient increase in another. An intermediate alternative involves maintaining the total stock of capital, but recognizing that there may be critical levels of different types of capital, below which society's (or an individual's, or a household's) ability to produce desired goods and services is threatened.

     Measuring the different forms of capital poses considerable challenges, and these in turn complicate assessments of sustainability. In an effort to improve such assessments, the World Bank (1997) sought to adjust national accounts and savings rates for investment in and depletion of natural and other forms of capital not traditionally included in those accounts. Accounting for changes in natural capital and human resources, they found that high-income OECD countries have had "genuine savings rates" of around 10% per year over the past several decades-less than traditional measures of investment, but still positive (and thus sustainable, at least in the broad sense). Asia and Latin America have also had positive genuine savings rates, most notably

in East Asia (with rates approaching 20% per year). Sub- Saharan Africa and the Middle East/North Africa, on the other hand, have consistently had negative genuine savings rates of -5 to -10% per year (World Bank, 1997). Such patterns and concerns continue today.

     The World Bank's measure of adjusted net savings currently begins with gross savings, adds expenditures on education, and subtracts measures of consumption or depletion of fixed (i.e., produced) capital, energy, minerals, forest products and damages from carbon dioxide and particulate emissions. In contrast to gross savings of 27.5% of GNI in developing countries and 19.4% in high-income countries in 2004, adjusted net savings after accounting for selected changes in human, physical, and natural capital were 9.4 and 8.7% in the two regions, respectively. Adjusted net savings were highest in East Asia and the Pacific (23.9% of GNI) and lowest in sub-Saharan Africa (-2.0%) and the Middle East and North Africa (-6.2%) (World Bank, 2006c). These findings reinforce concerns about sustainability by any of the measures described above. Similarly, the recent growth in crops, livestock, and aquaculture production has come at the expense of declines in the status of most other provisioning, regulating and cultural services of ecosystems (MA, 2005a).

1.3.2 Hunger, nutrition and human health

Some key characteristics of hunger, nutrition and human health are related to working conditions in agriculture and the effects of HIV/AIDS on rural livelihoods. Health is fundamental to live a productive life, to meet basic needs and to contribute to community life. Good health offers individuals wider choices in how to live their lives. It is an enabling condition for the development of human potential. Societies at different stages of development exhibit distinct epidemiological profiles. Poverty, malnutrition and infectious disease take a terrible toll among the most vulnerable members of society. Good nutrition, as a major component of health, has much to contribute to poverty reduction and improved livelihoods.

Health

Health has been defined as "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity" (WHO, 1946). It is an enabling condition for the development of human potential. The components of health are multiple and their interactions complex. The health of an individual is strongly influenced by genetic makeup, nutritional status, access to health care, socioeconomic status, relationships with family members, participation in community life, personal habits and lifestyle choices. The environment-whether natural, climatic, physical, social or at the workplace-can also play a major role in determining the health of individuals.

     The health profile of a society can be framed in terms of both measurable aspects-for example, access to clean water, safe and nutritious food, improved sanitation, basic health care, and education; mortality and morbidity rates for various segments of the population; the incidence of disease and disability; the distribution of wealth across the population-as well as factors that are less easily quantifiable. Among these are issues of equity or discrimination as