No. That there are differences in thinking speed is verifiable.
We can also verify that differences in thinking speed between individuals has a large component due to genetics, and also another large component due to environment. Everything from diet to the quality of parental interactions in early childhood.
What we can't determine is to whether genetics contributes to the differences in thinking speed between groups of people. We can identify important environmental factors like culture and racism. We can show that environmental facts matter. For example children of mixed race couples have a higher average IQ if they have white mothers. But nobody has found a way to measure what difference genetics might or might not make.
We can also verify that differences in thinking speed between individuals has a large component due to genetics, and also another large component due to environment. Everything from diet to the quality of parental interactions in early childhood.
What we can't determine is to whether genetics contributes to the differences in thinking speed between groups of people. We can identify important environmental factors like culture and racism. We can show that environmental facts matter. For example children of mixed race couples have a higher average IQ if they have white mothers. But nobody has found a way to measure what difference genetics might or might not make.