9.3: Tactile Evolution

Learning Objectives

• Visualize and explain morphological changes related to bipedalism
• Use kinesthetic learning to retain information about skeletal features of bipedalism

Supplies Needed

• Element reference sheets (included)
• Modeling clay

Readings

• Yoshida-Levine, Bonnie. 2019. Chapter 9: Early Hominins. Explorations.

Introduction

Modern humans are obligate bipeds: we are designed to always walk upright on two legs. Human ancestors, however, were not all obligate bipeds-- many were adapted for arboreal activities as well. In this activity, we will examine which skeletal changes are present in non-obligate and obligate bipeds, and we will use chimpanzees and modern humans as examples. Notably, there are also soft tissue changes that come with a shift to obligate bipedalism. Since the primary source of evidence for biological anthropologists is skeletonized and fossilized remains, we will be focusing on skeletal changes.

Specifically, students will construct models of non-obligate biped skeletal elements using modeling clay and then ‘evolve’ them into obligate skeletal elements. This activity allows students to develop a tactile sense of the skeletal differences and changes between non-obligate bipeds and obligate bipeds.

Steps

• Students may work in groups or individually. Each group or individual receives one ball of clay per skeletal element, the Element Reference Sheet(s), and Student Worksheet.
• Students use the clay to construct the element as it appears in a non-obligate biped, using the Element Reference Sheet for guidance. For this activity, a chimpanzee will be used, but other non-obligate bipeds may be used instead.
• After constructing the non-obligate biped element, students make appropriate changes in order to transform the element into one resembling that of an obligate biped. Students may add, remove, or sculpt the clay to make changes but they must not destroy the prior element. In this case, the modern Homo sapiens will be used as a model, although a different obligate biped may be used instead.
• Students should understand that the model non-obligate biped (i.e. modern chimpanzees) are NOT an ancestor of modern humans. The models are only used to display general characteristics of non-obligate bipeds. The line illustrations are simplified to facilitate easier modeling.

Review Questions

• Discuss the challenges you encountered in transforming the non-obligate biped model into an obligate biped model.
• Which morphological or skeletal changes seemed most significant and why?
• The proportionately smaller upper limbs, and S instead of C curved spines in obligate bipeds can be difficult to model. How did you address this? Why are these features important for obligate bipeds?

Adapting for Online Learning

If this is an in-person lab, rank how adaptable to online learning it would be(mark in bold):  Possible to adapt

Students could construct the models at home, using clay, and then photograph and upload into the learning management system’s discussion board. Students could then discuss each other’s models and the challenges they encountered.

Tips and Suggestions

After the activity, encourage students to read about regional skeletal anatomical variation between obligate and non-obligate bipeds on p. 329 of Explorations—this will help students to connect the kinesthetic knowledge that they have developed to specific anthropological terminology.

References

1. Yoshida-Levine, Bonnie. 2019. “Chapter 9: Early Hominins.” Explorations: An Open Invitation to Biological Anthropology, edited by Beth Shook, Katie Nelson, Kelsie Aguilera, and Lara Braff. Arlington, VA: American Anthropological Association. http://explorations.americananthro.org/