The construction of the shovel itself is ultimately due to past labour and land, as well as by the invention of the shovel (labour). Capital is always ultimately a product of labour and land. In accordance, rises in productivity in the absence of discovery of new land is because of unrealized past labour. Therefore, this newfound productivity is to be attributed almost entirely to labour.

This is why Adam Smith, for example, cites labour as the primary factor of production, followed by land with capital as the last. In modern parlance you might hear that said as "human capital is the most important", but human capital really is a politically correct way of saying "labour potential".