Before revision:  Products that require more capabilities are accessible to fewer countries (are less ubiquitous), while countries that have more capabilities have what is required to make more products (are more diversified). Our model implies that the return to the accumulation of new capabilities increases exponentially with the number of capabilities that a country has and that this convexity increases when either the total number of capabilities that exist in the world increases or the average complexity of products (the number of capabilities they require) increases.
After revision:  We solve the model assuming that the probability that a country has and that this convexity increases when either the total number of capabilities that exist in the world increases or the average complexity of products (the number of capabilities they require) increases.