A classroom exercise is described in which college students take part in
creating and supporting an evolutionary hypothesis that explains effort
grunting. The exercise holds their interest throughout and readies them to
understand hypotheses of animal and plant evolution. It informs them
about the dependence of cultural evolution upon biological evolution, and
it connects widely to curricula.
Key Words: Introducing students to evolution; effort grunting; cultural evolution.
When introducing students to evolution, there is much to be said for
exercises that, in Pobiner’s (2012) words, let the students see evolution “as personally meaningful,” tapping into their “enormous interest
in themselves.” I designed and teach such an exercise for my research
methods course, and it is suitable for college biology courses. It
involves an evolutionary hypothesis to explain effort grunting – that
is, why we often grunt when exerting ourselves close to the limit of
our capacities against a resisting force, as when
helping push a car out of a ditch, lifting heavy
barbells, or twisting off a tightly stuck bottle
Prior to the exercise, I guide the students
through the development of the hypothesis –
but they don’t yet know its substance. At key
points in the discussion, I stop to ask them
what they would do next, which gives them
a sense of contributing to its development.
(Teachers can use the method of this exercise
with the effort grunting hypothesis or with
another of their choosing.)
I assess the students’ understanding of the exercise with examina-
Step 1 (15 minutes)
tions and my judgment of the quality of their participation in class
discussions about it. On these measures the course receives good
marks. Steps 1 and 2 of the exercise are done in parts of two lecture
periods, and the final step 3 in a subsequent laboratory period.
I show the students two one-minute sections from among the many
You Tube videos of weightlifting competitions, one of a man, one of
a woman. “Tell me, why are they grunting?” I ask. Usually the students
say that grunting provides strength, but they cannot say how. The
class ends with an assignment to read sections of articles on effort
grunting (cited below in step 2) and do Google Scholar searches on it.
Step 2 (45 minutes)
We discuss the assigned readings on effort grunting. These establish
that – with one exception, described below – whenever we begin
what we expect will be a taxing exertion, we take a deep breath
and hold it, closing the glottis (the space between the vocal cords).
As our effort nears the most we are capable of, the glottis opens,
Second, we discuss two readings that agree with the students’
belief about effort grunting increasing strength. In Davis et al.’s
“What drove the
adaptations of the
involved in effort
The American Biology Teacher, Vol. 81, No. 7, pp. 474–478, ISSN 0002-7685, electronic ISSN 1938-4211. © 2019 National Association of Biology Teachers. All rights
reserved. Please direct all requests for permission to photocopy or reproduce article content through the University of California Press’s Reprints and Permissions web page,
www.ucpress.edu/journals.php?p=reprints. DOI: https://doi.org/10.1525/abt.2019.81.7.474.
FEATURE ARTICLE Why Weightlifters Grunt:
A Classroom Exercise That
Introduces Students to Evolution
• H. CHARLES ROMESBURG