General biology textbooks list symmetry asa key concept used by scientists to differentiate various groups of animals. Authors of these texts usually state that all animals except sponges have their body parts arranged along an axis. This arrangement may be one of radial symmetry, wherein parts are arranged around a central axis, or bilateral symmetry, wherein an animal's right half is a mirror image of its left half. Humans are placed in the group of bilaterally symmetrical animals (Phylum Chordata). But, how bilaterally symmetrical are we? Is our left half a true mirror image of our right half?
A quick tour of one's internal anatomy reveals a lack of complete bilateral symmetry because we only have one heart and it is located in the left half of our thoracic cavity. Even the heart itself, with its four chambers, has a left ventricle that is substantially larger than the right ventricle.
What do you think about our external anatomy? Is our left side a mirror image of our right side? Can you design an experiment to answer this question? Can you think of other symmetry questions that could be addressed from an examination of external human anatomy?
Check some of the links below to learn how we have been investigating this problem and review some of the data we have collected. In fact, why don't you start measuring your body and let me [Buzz Hoagland
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