Why do scientists consider cranial capacity when trying to determine the evolutionary history of humans?

Cranial capacity measures the interior volume of cranium or skull. It is usually measured in cubic centimetre. Cranial capacity has shown significant changes  in evolutionary history of humans hence it is studied while studying human evolution.

Increase in cranial capacity is associated with increased intelligence and development of more advanced skills as evident from the cranial capacity of humans which has increased from 440 cc in Australopithecus to 1350 cc in modern humans. Along with increase in cranial capacity; social complexity, communication skills and tool making skills also improved so they are often co related and studied together.

did you fail the test? xd