Over time, though long before American independence, the status of a child of mixed parentage was tied to their mother. In other words, the child of an enslaved mother and a free father was, under law, enslaved.
This legal innovation was a departure from English common law, where property and status typically descended from one's father. It was first established in English colonies in the Caribbean, where it was part of a series of slave laws that would form a template for the mainland colonies. In particular, Virginia enacted this law in 1662. In that colony, as in many others, there was a sort of spectrum of servitude—one that included free people of color, white and black indentured servants, and landless laborers.
By passing this law and other similar ones, the Virginia House of Burgesses clarified and rationalized the colony's social structure. It meant that the children of enslaved mothers and plantation owners, for example, would be enslaved, absolving the fathers of their parental responsibilities.
In intent and in practice, it was an important step in what one historian has called a "terrible transformation": the establishment of permanent, hereditary, and race-based slavery. Gone were debates about whether Christians or the children of free people could be enslaved. This would prove to be one of the most consequential and tragic developments in American history.