Activity: Brain vs. Bipedalism (Part B)

A. afarensis, lateral view.

A. afarensis, lateral view

A. afarensis, dorsal view.

A. afarensis, cranial view

H. sapiens, lateral view.

H. sapiens, posterior view.

H. sapiens, superior view.

P. troglodytes, lateral view.

P. troglodytes, posterior view.

P. troglodytes, superior view.

Part B: Cranial Measurements: Determine whether the brain size of A. afarensis was more similar to modern humans or modern chimpanzees. (Remember that the primitive condition is expected to be more like that of a modern chimpanzee).

• In this section of the activity, you will take three measurements: the cranial width (the widest part of the skull usually behind the ears toward the top of the head), the cranial length (the distance from the forehead just behind the eyebrows,) and the cranial height (the distance from the top of the skull to the bottom of the skull).
  

1. There are two options for the skull measurements. If your school has access to casts of a chimpanzee, a modern human, and an australopithecine skull, use digital calipers to measure in centimeters, the width, length and height of the each cranium. Or you can use the images available in the online bipedalism lesson on eFossils.org and eLucy.org. Estimate the cranial width, length and height using the scale provided in the top right corner of the image.

2. Calculate the cranial volume for the three specimens by multiplying the cranial width, cranial length and cranial height by 1.333 x 3.14, then divide your answer by 10. The measurements for a chimpanzee and A. afarensis are provided for you.

3. Answer the question based on your results.

• Was the brain size of A. afarensis more similar to modern humans or chimpanzees?