Symmetry, as it relates to the study of the structure of
the body, means that the size, shape, and position of a
body part or body parts are the same or equal on
opposite sides. A real or imaginary dividing line (known
as a vertical axis) separates the opposite body parts
into right and left sides.
If a person's left arm is the same size as his/her right
arm, this is an example of body parts having symmetry.
However, if one arm was longer than the other arm this
would be an example of asymmetry (lack of symmetry).
Body parts that have symmetry are referred to as symmetrical. They are proportional
and balanced. Symmetry is very important to subjective perceptions of beauty and
attractiveness, particularly facial symmetry. It is important to note that symmetry in
nature is approximate because it is actually rare for body parts to overlie exactly if
imprints of each side were folded over in half on one another. The same is even true for
plants because even leaves are rarely exactly symmetrical when folded over one
another. Despite this, some leaves and body parts will be classified as symmetrical if
they match up close enough.
Symmetry comes from the Greek word "syn" meaning "together," and the Greek word
"metron" meaning "measure." Put the two words together and you get "measure