Asymmetry in biology refers to the absence of symmetry in an organism's body plan or its parts. In other words, the organism or structure does not have matching halves or evenly distributed features around a central point or axis.
Understanding Symmetry vs. Asymmetry
To understand asymmetry, it's helpful to contrast it with the other types of symmetry:
- Radial Symmetry: Organisms with radial symmetry, like jellyfish, have body plans arranged around a central axis. Any cut through the axis results in roughly identical halves.
- Bilateral Symmetry: Organisms with bilateral symmetry, like humans, have a distinct left and right side. A single plane (the sagittal plane) divides them into mirror images.
Asymmetry, on the other hand, lacks any such consistent pattern.
Examples of Asymmetry in Biology
Several examples illustrate asymmetry:
- Flounders: Adult flounders are a classic example. They lie flat on the seafloor, and both their eyes migrate to one side of their head during development.
- Hermit Crabs: Hermit crabs have spiraled, asymmetrical abdomens that fit into the shells they inhabit. This shape is necessary to effectively occupy the shell for protection.
- Internal Organs (in bilaterally symmetrical animals): Even in bilaterally symmetrical animals, such as humans, internal organs often display asymmetry. For example, the heart is positioned slightly to the left, and the liver is predominantly on the right side of the abdomen.
- Snails: Most snail species exhibit a coiled shell that is asymmetrical. The direction of coiling (either clockwise or counterclockwise) is usually consistent within a species.
Significance of Asymmetry
Asymmetry can be an adaptation to specific environmental conditions or lifestyles:
- Flounders benefit from having both eyes on one side, allowing them to remain camouflaged on the seabed while still having a full field of vision.
- Hermit Crabs benefit from the shape of their abdomen, allowing them to curl into snail shells for protection.
Asymmetry can also arise from developmental processes and genetic factors.
