One part of the story I found fascinating is the overlap in infants' brains of the areas involved in tool use and hierarchical syntax. These diverge and specialize in adults. The homologous brain region in primates is involved in motor planning.

It's an interesting hint at the deeper evolutionary origins of language in the ability to plan complex actions, providing a neural basis for the observation that language and action planning have this common structure of an overall goal that can be decomposed into a structure of subgoals, which we see formalized in computer programs too.

This is an older reference (1991) where I first heard about it. there are more recent studies reinforcing various aspects of it but I didn't find one that was as comprehensive

https://doi.org/10.1017/S0140525X00071235