Sub-Saharan Africa (SSA) is the most important development challenge of the 21st century. Poverty is higher in most African countries than elsewhere in the developing world. According to the recently published Report of the Commission for Africa, economic growth in Africa is necessary for substantially reducing poverty. Among three proposed policy options, the Commission recommends that African countries invest significantly in agriculture. But policy makers in the region face a dilemma: which subsector within agriculture will yield the highest return for a given budget? This paper uses a computable general equilibrium model to simulate productivity gains in sub-Sahara African agriculture subject to trade-offs between gains in crops and gains in livestock. The simulated results suggest three conclusions. First, most of the sub-Sahara Africa economies gain more from research and development (R&D) investment in crops than from R&D investment in livestock but this conclusion is not true everywhere. The SACU (South African Customs Union) economies and Madagascar benefit from a sharing of R&D investment between crops and livestock. Second, when R&D is focused on food crops, a sharing of investment funds between crops and livestock is beneficial to other economies too. Third, in economies where a sharing of R&D investment between crops and livestock is beneficial (e.g., Botswana), general economic growth boosts the benefits from R&D investment in livestock.