1. Symmetry in Biology By Ashlen Mezrahi
Symmetry in biology is the balanced distribution of duplicate body parts or shapes within the body of an organism.
In nature and biology, symmetry is always approximate; they are never perfectly symmetrical
There are many different classes of symmetry in nature, as body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical.
The importance of symmetry in nature

2. Radial Symmetry: Characteristics
Taxon Radiata - polyphyletic assemblage of different phyla of the Animal kingdom
Top and bottom
Mouth
No head
No rear
No left and right side
The organism looks like a pie. This pie can be cut up into roughly identical pieces.
Polyphyletic: a set of organisms, or other evolving elements, that have been grouped together but do not share an immediate common ancestor.

3. Radial Symmetry: Jellyfish
C4v
Four rotations of 90 degrees

4. Special Case: Echinodermata
Starfish, sea urchins, and sand dollars
Bilateral symmetry at the larval stage
Fivefold symmetry as adults
Pentamerism
Five parts; 72° apart
Larval Stage: C2v

5. Fivefold symmetry in Echinodermata (C5v)

6. Bilateral Symmetry 99% of animals Mirror image; left and right side
Sagittal Plane
Internal organs asymmetrical
Evolved trait over 500 million years ago
C1v
There is an axis; on both sides of the axis the organism looks roughly the same

7. Bilateral Symmetry: Evolutionary importance
Forward Movement
Seeking food, shelter, home, and reproductive mates
Active, directed movement requires an elongated body form with head (anterior) and tail (posterior) ends
Development of a head and the concentration of sensory organs

8. Bilateral Symmetry (C1v)

9. Symmetry = Fitness Symmetrical Faces “more attractive”
Healthier; genetically fitter
Asymmetry: depression, anxiety, headaches and even stomach problems
Easier for the brain to recognize
Experiments with birds and insects revealed that females prefer to mate with males possessing the most symmetrical sexual ornaments
Female barn swallows prefer males with long, symmetrical tail feathers
Symmetry = Fitness

10. Facial Symmetry: Average Example

11. Very Symmetrical Face

12. Many more complicated symmetrical shapes in nature
Many more complicated symmetrical shapes in nature! Example- Platonic Solid: Icosahedron
2) Clorophyll protein of a pea
3) Circogonia Icosahedra Radiolaria
4) Radilarian organism
5) Aids virus
In geometry, an icosahedron is a polyhedron with 20 faces.
3)circogonia icosahedra radiolaria (a single cell organism living in water)

13. Sources