Researchers Injected a DNA Marker into Rhesus Monkeys at Different

Researchers injected a DNA marker into rhesus monkeys at different prenatal stages of development, let them grow up, and then looked at the neocortex neurons. They found that, depending on when during development they injected their DNA marker, the labeled neurons would be located in a different layer of the cortex with the most recently labeled ones located in layer II. What do these results suggest?

A) Cortical neurons settle into the six cortical layers in a random manner.
B) Cortical neurons settle into the first available spot in the cortex they find.
C) Cortical neurons settle in an inside-out manner, with neurons first populating layer VI.
D) Cortical neurons settle in an outside-in manner, with neurons first populating layer II.