The volume and mass of the brain has increased about threefold from early human ancestors such as Australopithecus afarensis, to modern humans, Homo sapiens. There have been several speciation events along the human lineage between these two endpoints. The model of punctuated equilibrium would be applicable to this trait if:

The question is incomplete as it does not have the options which are:

A. The threefold change happened in one concentrated burst.

B. The change was not consistent in direction, but happened in multiple bursts concentrated at each speciation event.

C. There was consistent directional selection toward a larger brain all along the lineage between the two species.

D. None of the above.

Option-B

Explanation:

The hominids evolved with time and the known hominid in modern time is the Homo sapiens or modern human.

The Homo sapiens like other species could have evolved from the older species through speciation and studies suggest that one of the major factors of human evolution is the size of the brain.

Two possibilities could explain the size of the brain that it could have evolved slowly with time called the gradual equilibrium or in bursts concentrated at each speciation event.

Since the punctuated equilibrium takes place in bursts until the species reach stasis is the most applicable condition for punctuated equilibrium to happen therefore Option-B is the correct answer.