Using the long time series available in the United States, studies report high rates of return to agricultural research (see section 7.6 for some examples). Because of the atomistic structure of production (comprised of relatively small firms producing multiple homogeneous products), few farms are willing or able to investment in formal R&D for their farms. Furthermore, because of the biological nature of agriculture, improved crop seed and animal breeds are self-replicating. This complicates the ability of innovators to protect intellectual property.