Activity: Brain Size vs. Bipedalism (Part A)

Foot Measurements: Determine whether A. afarensis had feet that more closely resembled modern humans or modern chimpanzees. (Remember that the primitive, or earliest, condition is expected to be more like that of a modern chimpanzee).

In this section of the activity, you will take three measurements: the distance between the hallux (big toe) and the second toe, foot length (the length from the tip of the longest toe to the back of the heel), and foot width (the widest part of the foot usually around the toe area). Scaled illustrations of a chimpanzee foot and an A. afarensis footprint from Laetoli are provided below.

  1. Trace your bare foot on a clean sheet of paper (you can use the back of this lesson).

  3. Using the provided scale, measure in cm the distances according to the instructions. Create or print out the graph below and record your results in the appropriate spaces.
  4. Calculate the hallux divergence index by dividing the foot width by the foot length.

  6. Answer these questions based on your results.

     - Did A. afarensis have a divergent big toe?

     - Did A. afarensis have a derived foot similar to modern humans, or a primitive foot          more like that of an extant chimpanzee?  Give a reason for your answer.