Thanks. I agree that tool making is an impressive skill, which requires a lot of cognitive resources, some of which might indeed be linked to activation in Broca's area. But here, too, there is no one-to-one correspondence: Broca's area is involved in many behaviors, so the fact that both sentence construction and tool making activate it, does not mean that they rely on the same neural processes, let alone the same genes. The evidence for the link between FOXP2 and tool making would be stronger if there is a family of people with a FOXP2 mutation (like the KE family I mentioned) who are impaired in tool making (or, if such a family does not exist, there could be correlative evidence from population-level studies). Don't know whether such evidence exist, that's why I was asked about the type of evidence you rely on.

The evidence from tool making to infer that the gene is involved (among other things, of course) in sentence construction is quite indirect. To me, that's quite a stretch. Besides, there is more direct evidence that FOXP2 is not involved in sentence construction (assuming the linguistic interpretation of this term): members of the KE family with a mutation in FOXP2 are not impaired in interpreting sentence structures. Instead, the common symptom is verbal dyspraxia, related to motor control and thus speech production.

Honest question: how do you know that FOXP2 is used in tool making? What kind of evidence shows this?

There is no specific gene responsible for language. Indeed, many are involved, and they're related to different aspects of language. FOXP2 is related to speech production (among other things), so perhaps Neanderthals had the ability to produce speech, but that wouldn't give them language.